Procedure for profiling a printer
Topics of Interest
Using Profile Prism Software
Quick start instructions for profiling a printer:
Note that scanning and printing software varies greatly from one manufacturer to another. While the quick start instructions below describe the overall process of creating a printer profile along with some recommended settings, we recommend reading and being familiar with the detailed instructions in the following section as well.
- Open the (ICC aware) software you intend to use to print photos.
- Open the print driver properties and select appropriate paper type.
- Set print driver settings according to recommendations.
- Turn off all color management/printer ICC profiles.
- Print the "printer-target-40.tif" file at its original size (approx. 7.92 x 5.77 inches), or
- If profiling an older model Epson printer in "no color adjustment" mode, you can use use "printer-target-bright.tif"
- Allow to dry/cure 12 hours.
- Cut printed target at dotted line. This leaves about about 1/8 inch black border around the printed color patches.
- Place both the IT8 reference target and the printed target on scanner glass.
- Place piece of black construction paper on top.
- Close scanner lid.
- Open scanning software set software settings as recommended here.
- Scan the targets and make sure targets are not rotated in the scanned image.
- Open Profile Prism and set "Type of Device to Profile" to "Printer".
- Bring image into Profile Prism and place four corner markers on IT8 ref.
- Evaluate the messages to determine exposure, clipping, etc.
- Click "Printer Target" radio button on top of window.
- Place four corner markers on printer target.
- Evaluate the messages to determine exposure, clipping, etc.
- After placing all eight corner markers, set PP options as follows:
- Type of device to profile: already set to printer
- Reference target: same as that shown on lower/right of ref. target
- Printer target: select the target printed in step 5 and 6 above
- Profile description: printer model, paper, and other info as desired
- File name: click "..." and select a name for the ICC profile
- Profile for: highest accuracy
- White balance: N/A
- Tone reprod. curves: N/A
- Initial adjustments: all "normal" or zero
- Click "Create Profile"
Note: Once the profile is created, you must use the same print driver and software settings selected in steps 2-3 above. To utilize the profile, simply select the profile as the "Printer ICC" or "Print Space" in the printing software.
The following describes the process for creating an ICC profile for a printer using Profile Prism:
I. Printing the Printer Target and Scanning the Result
Before we use the software to create a printer ICC profile, we must use our photo printing software to print a copy of the included "printer-target-40.tif" file. We will print this printer target at its original size (about 7.92 x 5.77 inches) and use our scanner to scan the print that the printer generated and the IT8 reference target at the same time.
- Software/print driver preparation: Profile Prism does not provide a facility for printing the printer target because the printer target should be printed through the software that you use to print images, i.e., the software that will be utilizing the printer ICC profile once it is developed. For example, if you use Qimage, print the "printer-target-40.tif" file with Qimage using the same program and print driver settings that will be used later (with the profile). Before printing the printer target, open Qimage (or other ICC aware software) and follow the checklist below:
- Make sure that all print quality options in your printing software are set to the same settings that will be used when printing your normal prints. Remember that profiles only work when printing "conditions" are exactly the same as they were when the profile was created (with the exception of the profile itself being in place).
- If the software you are using offers any final print sharpening, turn that option off (even if you normally use it). Extra sharpening is not needed and in cases where target alignment is not perfect, sharpened edges can cause false color readings. As an example of how to disable this feature in Qimage, click "Prints", "Print Interpolation" and move the final print sharpening slider all the way to the left. Just remember to go back to that window and click "Restore Defaults" before printing your normal photos.
- Click "File", "Printer Setup" and set all print driver properties as appropriate for the paper and type of printing you are doing. Remember that the print driver properties used when creating the profile must match exactly to the properties used when you later utilize that profile. For recommended driver settings, click here. Be sure to make selections that are appropriate for the paper you are using and most importantly, confirm that the paper you are using is compatible with your printer! Some third party papers or papers from different manufacturers may not work properly and may make profiling difficult/impossible. Also, turn off all photo enhancing effects or other options labeled "automatic". Options like "photoenhance" or "auto contrast" will not work with ICC profiles because they do not produce stable (static) results from print to print.
- Because we want to print raw data for the purpose of deriving a profile, make sure that your printing software is NOT utilizing an ICC profile for the printer. In Qimage, this only involves changing "Printer ICC" to OFF. This option is located on the lower right of the main window in Qimage. If using a photo editor, click "File", "Printer Setup" or "File", "Print Options" and look through all advanced settings to ensure that no ICC profile or "print space" is associated with the printer. For example, in PhotoShop 6 or 7, click "File", "Print Options", and check "More Options" and drop down and select "Color Management". Then make sure that "Print Space" is set to "Same as Source".
- Printer preparation: Make sure that you have the appropriate media/paper in the printer (the same media that you selected in the print driver above). Also, if your printer offers a utility for checking the print head nozzles, performing that test is highly recommended prior to printing the printer target. Clogged print nozzles can cause the generated profile to be inaccurate and performing a nozzle/print head check prior to printing can eliminate profile problems. If clogged nozzles are found, they MUST be cleaned prior to printing to ensure that all print head nozzles are operational.
- Printing the printer target: Now that we have selected the proper print settings for both the software and print driver and ensured that the printer is in good operating condition, we must print the file called "printer-target-40.tif" located in your Profile Prism folder (normally \program files\prism). In Qimage, this is accomplished by making sure that the "Image Fitting" crop button (scissors icon above the thumbnails) is up/not depressed, highlighting the "printer-target-40.tif" thumbnail from the \program files\prism folder, clicking "Custom", "Original Size", and then printing. Note that if you use a photo editor instead of Qimage to print the printer target, the default print size of "printer-target-40.tif" will be 7.92 x 5.77 inches. This size is fine and you should not alter the size or resample the image. Simply load the image and print the printer target at its default size. IMPORTANT: If you are using an ICC aware photo editor, you may be asked about color management when you open "printer-target-40.tif". If so, make sure that you do NOT color manage the image; select "Do not color manage" or "Leave as is". Once you have printed the color target, refer to the information below.
Evaluating your printed target: We recommend letting your test print of the color target dry/set for at least one hour, but ideally overnight. Nearly all inkjet printers produce prints that are dry to the touch immediately, however, many papers/inks take at least an hour for the final color to "set". During this time, there are often noticeable color shifts in the print, so you always want to make sure the printed color target contains "final color" before profiling.
Cutting out your printed target: Once the print has dried, use a paper cutter or razor knife/straight-edge to cut the printed target from the page. After cutting at the dotted line, you should be left with your printer target surrounded by about a 1/8 inch black border. Use of a rotary paper cutter is recommended because edges that are straight and "true" will make scanning and alignment easier.
Note about targets from older versions: Printer targets from old versions of Profile Prism must not be used. If you have targets/scans from versions prior to v4.0, they will not work and new printer targets will have to be printed using the included printer-target-40.tif file.
Printing the printer target at a different size: If your printer/paper is not able to accommodate the full 7.92 x 5.77 inch printer target, you may print the target at a smaller size. The larger the printed target the better, since the color patches are very small on the 9,261 patch printer target, but if your printer cannot accommodate the recommended (original) size, simply print the target as large as you can given the limitations of your printer/paper. If you must print the target smaller than about 5x7 inches, increase your scan resolution to 400 PPI when scanning to accommodate the smaller printed target.
Using the bright target: If you are profiling a printer that has very dark output (such as Epson printers in "no color adjustment" mode), we recommend using the optional "printer-target-bright.tif" instead of the normal "printer-target-40.tif". The "printer-target-bright.tif" is a brighter target that is more suited to print driver settings that produce dark output. Since Epson printers running in "no color adjustment" mode are the only combination that produces output that is heavily weighted to the shadows, do not use the bright target on non-Epson printers or Epson printers running in sRGB or "color controls" mode unless you have reason to believe that the output from your printer is darker than normal. IMPORTANT: If you do use the bright target, remember to set the "Printer Target" parameter to "printer-target-bright.tif" prior to clicking the "Create Profile" button so that Profile Prism knows which printer target it is working with.
- Scanning your printed target: Place the targets on the glass of your scanner against the edge of the scanner glass for easy alignment. Place the IT8 reference target on the top and your printed target underneath with the bottom edge of the IT8 target touching the top edge of the printed target as shown below. Since the quality of your printer profile will be directly related to the quality of the scan, click here to see the recommended scanner settings by manufacturer. Once you have set your scanning software accordingly, scan the two targets. The resulting scan should look something like this.
Note that your IT8 reference target that you received when you purchased Profile Prism is on the top and your printer target (labeled "printer-target-40" in the lower right) is on the bottom. Also note that it really doesn't matter which target is on the top/bottom. The above layout is used for simplicity. It is also not important that the two targets be aligned left-to-right or that the two targets are exactly the same size; the only thing that is important is that neither target appears rotated.
Important: See the importance of a good scan below for information on how to get a high quality scan and how to evaluate your scan to determine if it is acceptable for creating a printer profile.
Using the instructions above, we have used our photo printing software to print a file called "printer-target-40.tif" from our \program files\prism folder. We then scanned this printout along with the IT8 reference target that we received when we purchased Profile Prism. Profile Prism software will now be used to create a printer ICC profile. An accurate printer profile can be generated as long as both the printer target and IT8 target are scanned in the same scan, and that scan is of acceptable quality.
II. Using the Software
Step 1: Specify profile details
Before telling Profile Prism to generate your ICC profile, you need to specify a name, description and some options. Below is a description of each entry. If you are creating your first printer profile, you need only concern yourself with the underlined entries.
- Type of Device to Profile: Since we are profiling a printer, select "Printer" for this setting.
- Profile Description: Enter a description for the profile such as "Acme 800 printer profile - matte paper". If you leave this entry blank, it is possible that your ICC aware software may not be able to find the profile later.
- File Name: To save your profile to the system color folder (c:\windows\system\color for example), click the "..." browse button and enter a new file name in the "Save As" dialog or select an existing profile to overwrite. You may also type a file name directly into the edit box if you like, however, if a file name is typed without specifying a path, the profile will be saved in the folder where Profile Prism is installed. For example, entering "test" in the file name field will result in a profile named "test.icm" being stored in your \program files\prism folder.
- Reference Target: This reference file identifies the actual color for all color patches on your IT8 color target and is how Profile Prism knows the actual colors on your target. Simply look at the name of the data file listed here and make sure that the same name/number is listed on your reference target in the lower right corner. Note that the target "version" is sometimes referred to as the target "charge". If the version/charge listed in the dropdown does not match the version/charge listed in the lower right of the reference target, select the proper file name that matches. Once you have verified this entry, it is not necessary to change it unless you start using a different paper target that has a different version number stamped in the lower right corner.
- Printer Target: Refers to the color target printed in the "Printing the printer target" section. Select the target that you printed and then scanned: either "printer-target-40.tif" or "printer-target-bright.tif".
- Profile For: If the default "Highest Accuracy" is selected, Profile Prism will generate a printer profile that produces the most pleasing colors by compensating for perceptual differences of in-gamut and out-of-gamut colors, expanding the effective range of colors that are difficult to reproduce on printers such as bright blues and reds. If "Smoother Gradients" is selected, the printer profile will produce more "mathematically" accurate colors with smoother gradients, however as a compromise, some colors such as bright blues and reds may appear slightly shifted in hue.
- Tone Reproduction Curve: This option is disabled for printer profiling.
- White Balance: This option is disabled for printer profiling. White balance is determined by the "white" of the paper you are using.
- Brightness: Choose the "Normal" setting if you would like your profiled images to have an ideal tone curve (100% accurate brightness). Set this parameter to a positive value if you would like to increase brightness and shadow detail, and a negative value if you would like your profile to render images with darker shadows and an overall darker appearance. Note that the brightness here actually operates on a gamma curve, so a more accurate name for this parameter would be "gamma". The term "Brightness" is used simply so that it is a more recognizable and less confusing term.
- Contrast: Choose the "Normal" setting if you would like your profiled prints to have an ideal tone curve (100% accurate contrast). Set this parameter to a positive value if you would like your profile to render prints with higher contrast, and a negative value if you would like your profile to render prints with less contrast. Although the "Normal" setting will ensure accurate contrast in the profile, some photographers may prefer higher contrast results to add more "pop" to prints and increase separation between foreground and background. Most digital cameras and film processors deliver pictures with higher than normal/accurate contrast. Higher contrast tends to hide noise in the shadows and give a more "intense" or "sharper" feel to prints, however, it also tends to destroy some amount of shadow detail. Since anything other than the "Normal" setting is considered an "effect" or "enhancement", the other values are available purely as a personal preference since many people prefer more contrast than provided by a totally accurate tone curve. The "Normal" setting also provides the greatest possible detail in the print, so if your normal workflow includes any type of post processing using a photo editor, it may be best to use the "Normal" contrast setting since this will ensure that the print has maximum detail.
- Saturation: Choose the "Normal" setting if you would like your profiled prints to have ideal saturation. Set this parameter to a positive value if you would like your profile to render prints with more saturation, and a negative value if you would like your profile to render prints with less saturation.
- Bias Settings: The red, green, and blue bias values may be used to control unwanted color casts or to introduce different coloring effects. For example, if the profile produces a noticeable yellow cast, setting the red and green bias settings to negative values will reduce yellow in the profile. Bias changes can be made to the entire profile (if "bias includes grays" is checked) or only to non-neutral colors (if "bias includes grays" is not checked). Cameras can suffer from hue shifts when shooting under different light sources, while digital prints can be affected by metamerism (prints having a different appearance under different light), paper brighteners, and other issues. These are just a few examples where bias settings can come in handy by allowing manual "tweaks" when necessary. Note: always create profiles with bias settings at zero and only change the color bias in your profile if you deem it necessary.
- Metamerism Compensation: Leave at the left (default) position if the printed target reacts similarly to the reference target under the scanner's light source. Move to the right to equalize differences in metamerism (color shifts) between the reference target and printer target. See Metamerism and Printer Profile Accuracy below for details.
Step 2: Open and crop the image of the color target
- Click "File", "Open Image" and browse to the folder that contains the scanned targets. Select one of the images and it will appear in the image crop area in the upper right of the window.
- Next, locate the upper/left edge of the IT8 reference target in your image. To do this, use the horizontal/vertical scroll bars on the bottom or right of the image to scroll, or simply click on the image in the window and drag it left/right/up/down using the hand.
- Next, click the upper left crop corner button.
- Your mouse cursor will now change to an upper-left box corner when you move the cursor into the image area. Move this corner to the very edge of the target, placing it at the upper left edge of the black rectangle that surrounds the row/column labels as shown below. The corner marker is shown below as a black/white dashed line.
- Once positioned here, left click to place the corner mark. You will notice a red corner mark on the target image. If the corner mark is not exactly on the outside edge of the black corner as shown, simply repeat steps 3 and 4 until placed properly.
- Repeat steps 3 through 5, locating the other three corners of the target and placing their corner marks appropriately. Note that the top two corner markers should be placed at the edge of the outer/black rectangle surrounding the text row/column labels and the bottom two corner markers should be placed below the gray scale. Properly placed corner markers are shown below:
- Once all four corners of the reference target have been identified, the four "corner buttons" will only appear when you hover over them with the mouse. When all four corner buttons are "deactivated" and your target evaluation messages appear in the "Messages" area, you'll know that you have finished the cropping step. In addition, Profile Prism will overlay white "punchouts" on each color patch to verify alignment. The white punchouts should appear within each individual color patch on the target.
Note regarding the "Jiggle corners" option: If the "Jiggle corners" option above the image is checked, Profile Prism will "jiggle" all four corner markers to try to obtain the most accurate target alignment. Note that this option may move the red corner markers so that they no longer align perfectly with the edges of the target. This is normal since obtaining the best overall/average alignment of the white punchouts may require moving some/all corner markers slightly. To place the corners manually without Profile Prism moving them, simply uncheck the "Jiggle corners" box and place the four corner markers again.
- Simply move around the target and make sure that proper alignment exists by ensuring that each individual color patch contains a white punchout and that none of the white punchouts appear to overlap into neighboring color patches.
- Now we mark the four corners of the printer target (the target on the bottom of the scanned image). Check the radio button for "Printer target" above the scanned image and repeat steps 3-8, marking the four corners of the printer target as shown below. Note that since the printer target contains very small color patches, alignment is critical, so be sure to place the crop markers as close to the corners as possible. Notice that we are cropping at the tiny red corner markers at the edge of the color patches and not at the dotted line where we cut the target from the page. It also helps to have "jiggle corners" checked so that Profile Prism can assist you in fine tuning the alignment.
upper left crop corner
upper right crop corner
lower left crop corner
lower right crop corner
- Once the fourth corner of the printer target is marked, Profile Prism will display white "punchouts" for each color patch. Since the printer target contains so many small color patches, lighting variance is not accounted for on the printer target. Simply make sure that the white punchouts appear wholly contained within the color patches.
- After locating the fourth corner of both targets, messages will appear in the messages box. For printer profiling, the most important messages are those regarding "clipping". If many patches are clipped, you may need to modify your scanner settings and rescan the targets with settings that don't cause clipping. While a few patches will always be marked as min/max with "X" markers, strive to get a scan that has less than 10 "X" markers on each target. Generally, the less "X" markers, the better the profile.
Notes on Profile Prism feedback and messages:
Histogram: The histogram that displays in the lower left corner of the window after cropping a target can provide useful information about the capture of your color target. The histogram shows the distribution of pixel brightness values from left (black) to right (maximum brightness). The higher the curve, the more pixels contain that level of brightness. Ideally, brightness should be distributed from left to right on the graph with no large "clumps" of data on the left or right. A large spike on the left of the histogram indicates that some shadow detail on the target was clipped (not visible because it is completely black or zero in one or more RGB color channels). A large spike on the right side of the histogram indicates that some highlight detail on the target was clipped (not visible because it is completely white or maximum in one or more RGB color channels). Depending on the device being profiled, it may be impossible to achieve an "ideal" histogram where brightness is distributed throughout the entire 0-255 data range, but try to minimize "clumping" of data on the left/right as much as possible. Below are some examples of "good" and "bad" histograms.
The above shows a typical histogram of the IT8 target (on the left) and a typical histogram for a printer target (on the right). The red endpoint markers on the left/right are very short, indicating that only a very small amount of data is at minimum/maximum brightness.
The above histograms show data that is not uniformly distributed indicating improper exposure of the image. The graph on the left, although it certainly captures the entire range of brightness values in the image, is underexposed. With the histogram compressed into the lower portion of the graph, less data range is available for profiling and the resulting profile may not be as accurate as it could be if the brightness values were more evenly distributed. The image that generated the left histogram above will look dark and dull.
The histogram in the middle shows two problems. First, the red line on the right (although relatively short), indicates that some pixels in the image were at their maximum brightness (255). Also, notice how the data doesn't start until about 1/3 from the left. This indicates that there are no dark pixels in the image which compresses the capture range and makes black look gray. The image that generated this histogram will appear with a "haze" since contrast is lowered by the absence of true blacks and dark colors.
Finally, the histogram on the right shows a very large red (maximum) indicator on the right, indicating that many pixels were at their maximum brightness. This image is very overexposed and will not profile accurately. In addition, the histogram on the right also shows a red spike on the left indicating that some pixels were at zero (minimum) which can indicate loss of shadow detail. The image that generated the right histogram above will look super bright and oversaturated as well as being very contrasty. Unfortunately, images like this are what many scanners capture when set at their default values. Such images will have very vibrant color and a high level of "pop", but are far from realistic and will not profile well because much of the color target (in the shadows and highlights) cannot be captured due to data/pixels being "off the scale" by being too dark or too bright.
When possible, all of the above conditions should be avoided/minimized by tweaking the scanning software controls if possible. The problem must be corrected up front (at scan time) and must not be corrected with photo editors after the fact since this cannot bring back clipped data that was lost due to an overexposed scan. Overexposure or clipping can normally be addressed by setting "shadow" to zero, "highlight" to 255, and gamma to 1.0 in your scanning software. If the white patch in the lower left of your targets is not clipped, but there is still a red line on the right of your histogram indicating some values at maximum (255), it is possible that the scanner is oversaturating. In that case, reducing saturation by 25% normally will bring the saturation into range and prevent the saturation clipping.
Pixels at min/max brightness and clipping:
Pixels at min/max brightness: When Profile Prism examines an image of a color target, it will determine the range of brightness values captured in the target; that is, the darkest and brightest pixel values found on the image of the target. Due to limitations of the capture device or simply due to the brightness range found on the color target, these minimum/maximum values need not always be 0 and 255. An image of a color target, for example, may range from 4-251, meaning that the darkest pixels found were a brightness of 4 and the brightest were 251. Profile Prism will report the number of color patches that contained at least some pixels that were at minimum or maximum brightness. Obviously, there must always be a darkest and brightest patch on the color target, so at least two patches will always be reported as containing these darkest/brightest pixels. If a large number of color patches are marked as containing the darkest or brightest possible values however, it may indicate a problem. The message displayed will start with "Note:" if there are less than ten color patches containing min/max brightness and "WARNING:" if there are ten or more color patches that contain pixels at min/max brightness. A large number of patches that contain min/max brightness could indicate that the device that captured the image of the target simply "ran out of room" and bottomed/topped out. In a case where many color patches contained pixels of min/max brightness, since many pixels were found at min/max brightness, it is likely that at least some of them could not be properly recorded and the actual value could not be determined. Some things that can cause such a "truncated" range include: overexposure, oversaturation, inappropriate gamma setting, etc. If you get 10 or more patches at min/max brightness, try changing the exposure (shadow and highlight values on a scanner for example), the saturation setting, or the gamma setting to see if it brings more patches into range.
Clipping: In contrast to color patches that contain some bottomed/topped out pixels, clipping can occur in more extreme cases. Clipping is a condition where all pixels in a measured color patch are at their min/max value or there was some anomaly in the measurement that indicates that the values in those patches cannot be depended upon to be accurate. There are three conditions that can cause clipping: (1) every pixel measured in the color patch was at min/max value, (2) no incidental variation (noise) was found in pixels: they were all measured at exactly the same value, or (3) no difference was found between two consecutive color patches. Any of these three conditions normally indicates that the value measured is probably not accurate. Once again, try altering exposure, saturation, or gamma settings to compensate. The number of clipped patches (marked with a black "X" marker) should be minimized since this indicates that the entire target could not be captured and may result in less accurate profiles.
"X" markers and what they mean:
Green "X": A green "X" indicates that some pixels were at the minimum value (shadow threshold). Since some pixels were at minimum value and some were not, this often indicates that the color patches in question are simply the darkest measured patches on the target. If only a few patches contain green "X" markers, no problem is indicated. If a large number of green "X" markers appear however, it could mean that the color is at or near the minimum brightness value detectible by the device. In the case of many green "X" markers, your capture device may simply not be detecting dark colors reliably and this could be an indication of underexposure, inappropriate gamma setting, or simply a limitation of the device being able to capture darker colors.
Red "X": A red "X" indicates that some pixels were at the maximum value (highlight threshold). Since some pixels were at maximum value and some were not, this often indicates that the color patches in question are simply the brightest measured patches on the target. If only a few patches contain red "X" markers, no problem is indicated. If a large number of red "X" markers appear however, it could mean that the color is at or near the maximum brightness value detectible by the device. In the case of many red "X" markers, your capture device may simply not be detecting bright colors reliably and this could be an indication of overexposure or oversaturation.
Black "X": A black "X" on a color patch indicates that the color patch was clipped. This condition is worse than pixels being at min/max value since it indicates a problem where inaccurate capture of the color patch is nearly guaranteed. See "Clipping" above.
Scrolling through clipped patches: To locate and scroll through the clipped patches on the target to view them, simply click on the "WARNING/Note: n patches are at minimum/maximum value..." message in the message box on the bottom of the window. Each time you click on the message, Profile Prism will move to the next clipped patch on the target.
Densitometer: To further assist with evaluating the colors in your captured target image, Profile Prism offers a densitometer that can be used to view the measurements for each color patch. After all four crop corners have been placed on a target image, you can point to any color patch on that target and right click to see Profile Prism's evaluation of that color patch. You will be able to view the original measured color of the patch, the lighting variance, and the corrected color after considering lighting variance. Using the densitometer, you can determine which color channel is clipping (if clipping occurred), the exact color that was measured, how much lighting variation was found at that color patch, etc. Note that when examining color patches that are clipped with a black/green "X" marker, you will rarely see RGB values at their minimum/maximum value because you are viewing the RGB average over many pixels. Only some pixels were found to be clipped, so the average measured values will not normally show clipping.
Step 3: Generate the profile
Now it's time to sit back and let Profile Prism do its number crunching.
- Click the "Create Profile" button in the lower left corner.
- Note that Profile Prism will be performing billions of mathematical operations in the process of creating your profile, so it may take several minutes to generate a profile. You may follow progress by observing the progress bar at the bottom of the window.
- Note that once profile generation is complete, the location of your new profile is visible on the status bar at the bottom of the window.
- Make a final review of the messages displayed in the "Messages" box. Were any messages added? Profile Prism will add messages as the profile is being generated. These messages are:
- Printer/paper/ink dynamic range: This message gives you an indication of the dynamic range (contrast) available on the media you are profiling. The number displayed is the ISO brightness difference between white (paper with no ink) and black (100% black as rendered by your printer). The higher the number, the more dynamic range (contrast) the paper can handle. Colors will generally be more vibrant on papers with higher dynamic range.
- Printer/paper/ink coverage of Lab space: This message gives you an indication of the size of the color gamut on the media being profiled. The number displayed is the percentage of the full Lab color space that can be rendered by your printer on the media being profiled. The larger the number, the more colors your printer can reproduce on that paper, i.e. the larger the color gamut. The lower the number, the more compromises have to be made due to a more limited color range. Note that Lab color space is very large; even larger than the color gamut of the human eye. As a point of reference, sRGB color space (the standard PC/web display color space) only covers about 20% of Lab color space, so don't expect much more than about 15% to 20% coverage from your printer. Also keep in mind that this message does not indicate where the weaknesses in the color gamut occur, only the overall size of the gamut. 20% coverage from a printer does not mean that the printer can render the entire sRGB color space for example, since sRGB and your printer will cover a different portion of the color gamut (different set of colors) causing weaknesses in different colors.
- Printer profile usable range: This message gives you an indication of the range of values available to the printer profile. The ranges for the red, green, and blue channels are displayed separately and refer to the values that were discernable in the scan. A range of 0-255 indicates that there was a detectable difference over the entire range of printed values. A narrow range such as 64-255 indicates that there was no detectable difference in printed values from 0-63, meaning that the darker values in the range all looked "black" (at least to the scanner). Ranges such as 0-255 up to 26-255 should be considered typical. Ranges narrower than 26-255 could indicate that your printed output is too dark for the scanner to read or that shadows are blocked. Recheck the settings that you used for printing your printer target and try to decrease ink density or use other print driver controls to print a brighter and more uniform target. Printing a target on an Epson printer with the driver set to "no color adjustment" can often produce a print that is too dark for typical scanners to read accurately. See the section on print driver settings to correct this condition.
- Smoothing required: Profile Prism actually tests your printer profile after it is created to determine if posterization (banding) exists due to abrupt shifts in color gradients. After examining the profile, adequate smoothing is applied to the profile to eliminate posterization artifacts. The "smoothing required" message indicates the level of smoothing that was required to achieve smooth gradients in the profile. Profile Prism always performs a single pass to ensure smooth transitions, so the minimum is 1 pass. If posterization (banding) is still detected after a single smoothing operation, more passes will be performed until the posterization artifacts are minimized. The more passes required, the harder Profile Prism is working to correct deficiencies in the print/scan. Normal smoothing requires between 1 and 4 passes. If more than about 4 passes are required, it may be time to examine your print settings (paper type, color mode, etc.) to ensure that ink delivery is appropriate for the paper you are using and/or examine the scan settings to ensure that you are getting enough detail in the scan in the shadows and highlights. The most common causes of needing extra gamut smoothing are: (1) the scanner is not picking up reliable data in the shadows; try different scan settings and/or (2) a paper type was selected in the print driver that applies either too much or not enough ink; experiment with different paper types.
- WARNING - color patches detected out of correction range: Like an evaluation of "Fail" in the spectral sample range, this warning message is very rare and will normally not appear. It indicates that Profile Prism found color patches on the target that are so far off that it could not correct those colors completely. While some color patches may not be 100% accurate in the profiled image if this message appears, it doesn't mean that the error will be visible. In fact, the profiled colors will always be more accurate than the original. This message simply means that Profile Prism was only able to improve the colors but not able to make them 100% accurate. This message usually indicates that there are large errors in color rendering by the device in a small range of colors in the spectrum.
NOTE: After you click "Create Profile" and the profile creation process has completed, the final messages displayed in the "Messages" box will be saved and associated with the image file that was used to create the profile. To recall the messages for a previous profiling session, simply click "File", "Recall Messages For" and select the image file used to create the profile. The messages will be recalled from the last time a profile was created based on that image.
The importance of a good scan
A fact that is rarely mentioned by other profiling software manufacturers is the importance of a high quality scan of the two color targets. The quality of your scan will affect the quality of your printer profile. Since we are using a scanner as a crude spectrophotometer for the purpose of calibrating your printer, your scan of the two color targets must have two important characteristics: consistency and quality. Consistency relates to setting up your scanner and color targets so that the hardware itself produces the most consistent scan. The quality of the scan depends more on the software settings used in the scanning software. Please click here to see the recommended settings to use for your scanner.
What about using a digital camera in place of a scanner to capture the two targets?
Scanners are normally much better at capturing images of the targets than digital cameras because they offer a more controlled (static) environment. In addition, due to the very large number of color patches on the printer target (9,261 versus 288 for the IT8 target), alignment is critical. It can be difficult if not impossible to capture an image that is aligned well enough to accommodate the printer target. For this reason, capturing printer targets with a digital camera is not recommended.
III. Metamerism and Printer Profile Accuracy
Metamerism is defined as a shift in color when viewing the same subject under different types of light sources. If you have ever matched clothing or fabric by examining against a swatch in a retail store only to find that what matched perfectly in the store is quite different under your home lighting, you have fallen victim to metamerism. Some types of lighting are good for evaluating colors while other light sources are inherently poor. Sunlight, for example, is a very good light source for evaluation of color due to direct sunlight having a smooth, full spectrum of color. Fluorescent and incandescent lights are examples of light sources that often bring out metamerism due to their poor coverage of the light spectrum.
All photographic media are prone to metamerism to some degree. To make matters worse, the cold cathode fluorescent tubes used as light sources in most scanners can bring out metamerism in prints since scanner light sources are neither full spectrum nor do they offer smooth coverage of the light spectrum. The photographic media used to create standard IT8 targets often shifts toward magenta under scanner illumination. The printer target from your printer, however, is not likely to exhibit the same color shifts as the IT8 target since it is not printed with the same media/colorants as the IT8. In other words, when profiling a printer using a scanner, the reference target and your printer target may have different color shifts under your scanner's light source. Some compensation is often needed in order to equalize the effects of metamerism on the two targets.
Unfortunately there is no way to measure the effect of metamerism to compensate for it automatically. You may find yourself scanning a variety of media and the characteristics of that media with respect to metamerism will not be known. Fortunately, Profile Prism does offer methods of dealing with metamerism when profiling a printer. The "Metamerism Compensation" slider may be used to manually balance the effects of metamerism on the two targets. If your printed target reacts the same as the IT8 target under your scanner's light source, your profiled prints will look neutral and the slider should be in the left position (default). If your printed target reacts differently, causing a magenta shift in your profiles, move the slider to the right to cancel the color shift. Usually, setting the slider between the third and fifth notch is enough to remove visible color casts caused by metamerism in profiles. In extreme cases where there is a large difference in color shifts between the IT8 and printed target, you may find that the slider does not offer quite enough correction. In these cases, the red, green, and blue bias settings may be used to compensate further.
In addition, you may also use the matte CRxxxxxx target to profile your printer (see camera profiling instructions for information on use of the matte target). The matte target is less affected by metamerism than the IT8 target and may provide more balanced results under your scanner's light. Simply replace the IT8 target in the scan with your matte CRxxxxxx target and scan the CRxxxxxx target with your printer target.
Note that since scanners are not capable of capturing spectral information, the adjustments you make with respect to metamerism will depend on factors such as the actual light source in the scanner, the light source you plan to use for your displayed prints, and the difference in metamerism between the reference target and the printed target. Since we do not have the tools to measure what your prints will look like under different lighting, compensating for metamerism using scanner based profilers is more art than science. While most users will probably be content with their profiles without even considering the effects of color shifts under different light sources or trying to compensate for metamerism of color targets, those who demand the most exacting color will be able to use various tools available in Profile Prism to get the most out of their printer profiles.
IV. Utilizing and Evaluating Profiles Generated by Profile Prism
Note that the above instructions relate to generating an ICC profile for a printer. Since an ICC profile is a standardized method for describing how a printer responds to color information, using these profiles to obtain accurate prints is a task left up to your printing/imaging/editing software. Inexpensive software does exist which allows you to fully utilize ICC profiles for color management of images, batch conversion, etc. One such ICC aware application is Qimage, also produced by ddisoftware, Inc.. As stated elsewhere, consult the help or users manual of whatever ICC aware imaging/editing software you are using for assistance in making use of your ICC profiles once created. In Qimage, some relevant links that provide help and understanding of ICC profiles are:
Understanding ICC Profiles
Qimage Learn by Example: ICC Profiles Section
Note that whatever software you use, there is a standardized folder for which ICC profiles are normally stored. The following are "standard" locations for ICC profiles depending on the operating system used. It is recommended that you save your profiles in these locations since most software will look here for them:
Windows 95, 98, 98SE, ME: \windows\system\color
Windows NT/2000: \winNT\system32\spool\drivers\color
Windows XP: \windows\system32\spool\drivers\color
Once your ICC profile has been placed in the proper folder, it should be accessible from your ICC aware printing software. When utilizing the profile, remember to leave all software and print driver settings as they were when you printed your printer target for scanning, and enter the printer ICC profile into your photo editor/printing software as the "Printer ICC" or "Print Space". For example, in Qimage, leave all software/driver settings as they were when the target was printed, and activate your ICC profile under "Printer ICC". In PhotoShop 6 and 7, make sure to set all print driver settings to what they were when the printer target was printed (PhotoShop will not remember them like Qimage), and click "File", "Print Options", "More Options", "Color Management" and set "Print Space" to your printer ICC profile. It is important that the ICC profile not be utilized in the print driver itself under "ICM" in the print driver. Your print driver has no knowledge of what color space to use for your images themselves and therefore cannot properly manage color from start to finish like your photo editor or ICC aware photo printing software.
Most ICC aware printing software offers a choice of rendering intents when a printer profile is used. A rendering intent is simply a method used to match colors in your prints. Since your printer is very limited in color reproduction and cannot reproduce all colors in all images, selecting different rendering intents allows you to make compromises that best suit the images that you are working with. We recommend using one of the following two rendering intents when using your Profile Prism printer profiles. Note that the selection of rendering intent is made in the printing software at print time, not in Profile Prism.
Perceptual: The perceptual intent is the most commonly used intent for photos. The perceptual rendering intent scales color saturation to give the illusion that more colors are being reproduced. Generally, photos will appear less saturated (a bit duller) especially in areas of bright colors, however, the overall relationship between colors is maintained. Since bright, saturated colors are desaturated and "scaled to fit", the entire color gamut is affected to some degree. This means that while perceptual rendering is visually pleasing due to maintaining a good relationship between colors, no colors are reproduced exactly, even those that are reproducible by the printer.
Relative Colorimetric: The relative colorimetric intent is often used with images that have a limited color gamut (duller colors or specific colors in a small range). Relative colorimetric intent ensures that all colors that are reproducible by the printer are reproduced exactly (as closely as the profiling process allows). Colors that are not reproducible (too bright or saturated to be reproduced by the printer) are "clipped" to the edge of the color gamut. Images printed with relative colorimetric rendering intent usually appear more saturated than those produced via perceptual intent because in-gamut colors are not scaled or "dulled". In many cases, relative colorimetric intent can produce beautiful and highly accurate images, however, limited gamut coverage can cause posterization and "blowouts" when colors are printed that are outside the range of the printer.
We recommend using perceptual intent on a general basis because it will cause the least number of "objections" regarding color. Since no rendering intent is perfect for all images, however, you may find a few images that respond better to one particular rendering intent. It is often best to use perceptual intent unless problems are noted with a specific image, at which time you may find improved results using relative colorimetric intent.
Evaluating Profile Effectiveness
Perhaps the best way to evaluate the effectiveness of a printer profile is to put together a series of images from your own (also profiled) camera/scanner. Try to pick a set of about 5-10 images with a wide range of subjects and color and print them using your Profile Prism printer profile. Since only the color of the prints needs to be evaluated, it is often only necessary to print small (~3x2 inch) prints on one page to be able to judge color accuracy.
There are also standardized test images available on the web and on the Profile Prism FTP site. Go to the Profile Prism Homepage and then click on the "Support" link to access the Profile Prism Software Update & FTP site. Note that this site is password protected and is only available to registered Profile Prism users.
Editing Printer Profiles
Profile Prism includes a profile editor that allows manual adjustments to be made to printer profiles. See the profile editing section for information on how to make manual adjustments to printer profiles.