Frequently Asked Questions
Q: Will the use of ICC profiles ensure 100% color accuracy in all images?
A: Yes and no. The extent to
which any device can reproduce color depends on the gamut of
colors that the device covers. Due to inherent hardware
limitations, digital cameras, scanners, and printers can only
capture or reproduce a subset of the colors visible to the human
eye. The subset of colors that the device can reproduce is called
the device color gamut. Colors outside of that gamut are
physically impossible to reproduce on the device; they must be
scaled to a color that is inside the gamut. Cameras and scanners
have large enough color gamuts that most of the colors that you
see in the physical world can be captured exactly, however, they
are still incapable of capturing all colors that the human eye
can detect. On the other end of the spectrum are printers, which
have very small color gamuts. While the inks in your printer are
designed to allow reproduction of color that covers most subjects
in typical photos, even six color inkjets leave a wide range of
colors that are physically impossible to reproduce. Bright,
saturated blue is an excellent example of a color that is not
reproducible on a printer. Since your printer must create the
color blue by mixing yellow, magenta, and cyan inks, it has a
very shallow range in the blue area of the spectrum.
Take a look at the blues in the sample above. Although the above shows a relatively wide range of blue colors, none of these colors can be reproduced by a CMYK printer, even the wider gamut six color inkjets. While it is impossible to reproduce the above colors, it is possible to produce colors that have a similar "appearance" to the eye. There are several methods for doing this. The entire color range can be scaled so that it fits within the gamut of colors reproducible by the printer. The result of this scaling approach, however, is an appearance of very undersaturated color. A second method is to reproduce all colors within gamut exactly, while clipping non-reproducible colors to the edge of the gamut (nearest color). This works well for less saturated colors that are within gamut, but causes posterization (uneven blending of colors) when rendering colors outside of the gamut. A third method is some combination of scaling and clipping. Unfortunately, since some of your photos may contain colors that are beyond the capabilities of your printer, none of these methods can ever make your printed images look exactly like what is on your screen! The ability of a profiling tool to create an accurate appearance of color when color is outside the gamut of the device is where color science leans a bit toward "color art". When reviewing images of various subjects and color content, try to keep this in mind.
Q: Since Profile Prism uses a scanner to scan printed results when developing printer profiles, will my scanner be of sufficient quality to create accurate printer profiles?
A: It often depends more on the scanning software than the scanner hardware itself. If you have access to good scanning software that allows you to acquire a raw scan with color management turned off, most likely your scanner will do the job. If all you have are the most basic controls offered by the "standard" Windows interface (brightness and contrast), you may not be able to operate your scanner in a mode that allows it to capture the entire color target. When set to default scan settings, most scanners will clip both the shadows and highlights as they try to create an image with too much contrast. This means that part of the color target is actually not captured. It is therefore often necessary to turn off scanner color management to obtain a "raw" scan. To find out if your scanner has the range necessary to capture a color target, try downloading http://www.ddisoftware.com/prism/help/printer-target-40.tif. Print that target pursuant to the instructions in the profiling a printer section and scan the result using the scanning tips in that section. After scanning the printed target, load the scanned image into a photo editor. Examine the RGB values of the first few color patches on the target (upper left) and the last few (lower right). If any of the first/last few color patches are clipped at 255 or 0, or there is no difference between RGB values in those patches, your scanner has clipped some of the image; try to reduce the scanned exposure so that you can obtain an original scan where the patches are not clipped. If you are unable to overcome shadow/highlight clipping in your scans, the quality of your printer profiles will suffer. The worse the clipping problem, the less accurate your printer profiles will be.
Q: Can Profile Prism generate ICC profiles for any printer and any paper/ink type?
A: Absolutely. Be aware, however, that your printer will probably produce the most consistent color on paper designed for your particular printer. Many third party papers and ink appear to do a good job on the surface, but actually suffer from ink puddling, bronzing, banding, or other artifacts that can affect accurate profiling. Problems like ink puddling on the surface of the paper rather than being absorbed or drying properly are obvious, however, other problems can exist that reduce the ability to create accurate profiles. Your print driver depends on being able to place individual ink dots on the page to be able to create accurate and consistent color. One problem that often occurs with "cheaper" papers is that the ink does not dry when it hits the surface of the paper. This can cause individual droplets of ink to combine and produce rather random patterns/colors on the printed page. Often the result is reduced shadow detail because colors in the deep shadows blend and produce "muddy" colors. This is very difficult to detect in your "average" photo but often surfaces when printing the "printer-target-40.tif" image. Once you have printed the printer-target-40.tif file, examine the print by looking at it at a sharp angle, allowing room lighting to reflect off the surface of the paper into your eyes. If you can see a difference in the amount of "glossiness" on the surface of the paper (some color patches appear more glossy than others), the paper is causing bronzing where ink is drying on top of other ink rather than on the paper itself. This bronzing will cause reduced shadow detail and possible color shifts because ink has been blended/splotched together.
Q: I am using a test image that I found on the Internet to evaluate printer profile effectiveness. While much of the image looks accurate, there are some colors that just don't match what I see on the screen. Some blue colors exhibit a color shift, etc. Am I doing something wrong?
A: Probably not. Many test images that were produced for the purpose of evaluating printed color contain large areas of color that are physically impossible to create on your printer. Test images intentionally include a large gamut of colors so that the profile can be evaluated as to how effectively it "fools the eye" with regard to the colors that cannot be reproduced on your printer. As a result, these test prints need to be evaluated on two fronts. First, evaluate the profile for how effectively it renders colors that are within the color gamut of the printer, like skin tones, less vibrant colors, neutrality of gray scales, etc. Second, evaluate the appearance of other colors that may be outside the "reach" of your printer, like bright saturated blues, deep reds, etc. This latter group of colors can never match what you see on screen, but a good profile should do a reasonable job of managing both colors inside and outside the gamut, leaving no large or noticeable errors in any one area. While many "mechanically produced" test images may have many colors outside the range of your printer, your printer is capable of reproducing the majority of colors in most "average" photographs. It is often best to compile a page of 10 or so small 3x2 prints of varying subjects and color. If you save this compilation of "typical" photographs, you can use that set to print and compare differences in profiles. Since test images that have a large range of colors will always "highlight" the deficiencies in your printer's color gamut, it is natural for the eye to focus on areas in the image that don't appear 100% correct. While evaluating test images is a useful exercise, it can also be deceiving in that it forces you to focus on a small band of colors that may rarely ever appear in your real photos. If you get "stuck" focusing on one particular area of colors in a test image, try printing a batch of 10 or so "real" photos to see how noticeable the problem really is. Remember that some online test images actually contain colors that are beyond the reach of even your camera/scanner, so with regard to the photos you take/scan, your printer may actually never see those colors in a real photograph! Some good test images are available on the Profile Prism FTP site which is accessible via the Profile Prism Software Upgrade and FTP Site (for registered users only: username/password required).
Q: My printer profile is generally accurate, but most skin tones appear too red. Is there anything I can do?
A: First, realize that there is sometimes a difference between "accurate" skin tones and "pleasing" skin tones. Many people prefer skin tones that are a little "deeper" or "warmer" than they appear in real life. For this reason, always compare prints to the original skin tone to make sure there is really a problem. If so, many times the problem can be traced to the input profile, not the printer profile. What profile are you using for your camera or the scanner used to capture the image in the first place? Remember that an accurate input profile is just as important as an accurate printer profile! If you see any unexpected color shifts in your prints, the first thing to try is creating an accurate profile for your camera or scanner and using that with your printer profile. Profile Prism allows you to create camera, scanner, and printer profiles to close the loop on color management, so it is not advisable to simply create a printer profile and try to use it with your photos without profiling the camera or scanner you used to capture the photos as well. In addition, make sure you check the documentation for the ICC aware photo editing/printing software that you are using to make sure that you are assigning both the input (camera/scanner) profile and the output (printer) profile appropriately. Problems often occur from users assigning profiles inappropriately or "backwards" or "double profiling". If you have created a camera profile and then open an image from your camera and select "Convert to Profile" for example, you are profiling backwards. A camera profile is an input profile that you convert from, never to. For this reason, "Assign Profile" is the appropriate procedure for using a camera profile in PhotoShop. In Qimage, your "Printer ICC" should be set to your printer profile, and when you add images to the queue, an appropriate camera/scanner profile should show on the far right of the text line in the queue. If you see a profile that is not appropriate for a camera/scanner in the queue (if you see a printer profile for example), you need to fix your input profile table under "Settings", "Color Management" so that the proper input profile is being used.
Q: My printer profile is generally accurate, but has a loss of shadow detail or appears too dark. Can this be corrected?
A: Many times this is a result of the original print being so dark that the shadows are at least partly clipped by the scanner. If you cannot choose print driver settings that produce a brighter baseline print up front, you can try modifying the "brightness" parameter on Profile Prism's main window before generating a profile. Since the brightness setting operates on a gamma curve, setting the brightness parameter to a positive value (+4, +6, etc) will brighten the overall print (especially the shadows) without blowing out the highlights.
Q: My printer profile is generally accurate, but there is a color cast in what should be neutral colors. What causes this?
A: Take a look at your scanned image of the printer target. Is the white color patch on the top/left clipped (a value of 255) in any of the RGB channels? If so, it is impossible to get an accurate reading for the white point of the paper. This can cause a color cast in neutral shades (grays). Try to reduce the exposure on your scanner and see if you can bring that color patch into range (less than 255 in all three channels). If the color controls in your scanning software are insufficient to reduce the exposure, some have achieved success by scanning with the scanner's cover/lid in the up position in a darkened room. Others have used one or more clear sheet protectors to darken the image of the targets. Remember that overexposure must be corrected in the original scan. Never use a photo editor to reduce exposure after the fact; you may fool Profile Prism and not get an overexposure message, but all you have really done is reduced the clipping value from 255 to some lower value, effectively only reducing capture range and not correcting the problem. Finally, if you have your scanner's preview turned off, it is possible that scanning twice will result in a more accurate exposure in the second scan. Some scanners set exposure based on the last scan, so scanning twice and using the second scan can sometimes help bring exposure into range, especially when preview is turned off and the scanner has no knowledge of what is on the scanner glass until it is scanned the first time.
Q: When I scan the two targets for printer profiling, I am having a difficult time cropping the corners of the printer target so that the small punchouts on that target align properly or the punchouts are so small that I can't easily tell if they align properly. Can I increase the resolution of the scan to allow better cropping?
A: There are two ways to address this issue. First, you can print your printer target larger than 5x7. For example, if you print your printer target at a size of 6 x 8.5, inches your printer target will still fit on the scanning bed (along with your Prism target) but the target will appear much bigger on the scan, allowing more leeway for corner cropping. You can also increase scan resolution, however, going above 400 PPI can sometimes bring out individual dot patterns. In the worst cases, you can print your printer target at 6 x 8.5 and scan at 400 PPI. The resulting image should have plenty of resolution to deal with alignment of the 9,261 color patches on the printer target.