Profile Prism
Procedure for profiling a digital camera

Notice: As of February 2007 we no longer offer a matte target.  After years of testing, we have determined that the accuracy of the glossy IT8 target is superior to the matte target, making the IT8 target a better choice for profiling all devices.  In addition, with careful preparation, the glossy IT8 target can be used to profile cameras with no issues related to reflections or glare, so a matte surface is not necessary.  The following is taken from one of Mike Chaney's Tech Corner articles at Steve's Digicams and it describes how to profile a camera using the included IT8 target and Profile Prism.

I. Profiling a Camera with an IT8 Target

I am often asked about camera profiling in one context or another, and even challenged by other professionals as to whether or not it is even possible to develop ICC profiles for digital cameras.  As I often say, the answer can be complex and may depend on many factors, but let's break it down into a few key points that are relatively easy to understand.


Profiling a camera: the process

In the early days of digital cameras, it was possible to produce a profile for cameras shooting in JPEG/TIFF mode mainly due to the fact that some cameras produced gross errors that could benefit from correction, even if the result wasn't completely "accurate".  Now, most cameras comply reasonably well with the sRGB color space and many more advanced cameras even offer an option of sRGB or Adobe RGB as the color space used by the camera.  When we have a relatively recent camera model and/or a color space selection, it is rarely beneficial to try to develop ICC profiles for the camera shooting in JPEG/TIFF mode because it is difficult to impossible to produce corrections that result in any consistent improvement.  If we shoot in raw mode, however, most raw conversion tools offer an option to turn off color management so that custom ICC profiles can be created/used.  With color management turned off, the raw data offers a much more consistent starting point, and profiling becomes not only possible, but often quite beneficial.

The process, at least conceptually, is very simple.  Take a shot of a color target in raw mode, develop the raw image with color management turned off in the developing software, and use a profiling tool to create a profile from the image of the target.  The profile can then be activated in the raw developing tool.  That said, the actual process itself can get a bit complex if we want to ensure a quality profile.  You need to get a good shot of the target under good lighting, and you need to use a profiling tool like Profile Prism that was designed with camera profiling in mind as camera profiling requires specialized options like the ability to normalize tone curves and let the device dictate white balance.  There are other high-end (read expensive) tools that allow you to develop camera profiles.  These tools offer specialized targets and software, but I find that with some care, it is possible to match or even exceed the performance of these "high dollar" tools with Profile Prism and a standard IT8 target!


The problem, the solution

Before we start with the details, it is appropriate to inject a bit of reality here.  Many raw developing tools, while they are designed to produce the best color possible, just weren't built using any real "scientific" means for color accuracy.  Some use a simple color matrix to tweak color so that it looks acceptable and many don't employ reasonable tone curves to ensure good shadow detail.  In layman's terms, this is the reason that it is often possible to develop ICC profiles for raw images that result in better color reproduction than the raw tools offer out-of-the-box.

If we can develop a profile that improves color over the "default" color reproduction of the raw developing tool, we can say we have a successful/useful profile.  Some may question whether or not it is possible to develop a single profile that works under all lighting conditions, or whether it is imperative to develop one profile for each lighting condition: sunlight, fluorescent, incandescent, mercury vapor, etc..  Again, the true scientific answer here can get complex, but I've found that when profiling the true raw data, a "generic" profile can be developed using direct sunlight.  As lighting conditions (color temperature) shift from direct sunlight to warmer lighting such as incandescent lighting, the profile will become less accurate but the shift is not normally so extreme as to cause gross errors.  This is, in part, because the color filters used on the image sensor aren't changing under different lighting.  Their overall response is the same under different lighting and color temperature only affects the proportions of red, green, and blue recorded by the sensor.  A good profiling tool can discover the overall color characteristics of the sensor which tend to be valid over a wide range of lighting conditions.  Here, the closer you can get to the actual raw data the better, because up-front color corrections only tend to multiply color shifts, so a raw tool that offers the ability to process the raw data without injecting color corrections will work best.

While some may choose to develop different profiles for different lighting, and that's certainly optimal, a generic profile for sunlight should work under a variety of conditions.  Shooting the IT8 target in direct sunlight helps to reduce any metamerism of colors on the target and ensures a good match to the data file that tells the profiling software what the color on the target should look like.  Shooting in direct sunlight also offers the ability to eliminate glare as the IT8 target is a glossy target that, when not shot under the proper conditions, can certainly produce glare which will make the profile useless.  Shooting with the light hitting the target at an angle is imperative to eliminate glare/reflections and due to the fact that our light source (the sun) is so far from the target, we don't have to worry about the light being brighter on the side of the target closest to the sun as we would with angled studio lighting!  Here's how to shoot an IT8 with no reflections or glare:

  1. Of course, a lot depends on your location and the time of year, but in general, the best time to shoot the target is either 1-2 hours before mid-day or 1-2 hours after mid-day.  Try to shoot on a day with minimal clouds so the sun isn't changing intensity/color as you shoot.

  2. It is helpful to attach your IT8 target to a piece of thick cardboard using small tacks or pins at the corners or even tape at the corners as an IT8 will tend to curl and bend when it heats up in sunlight.

  3. Try to find a room where light is entering a window/door at a sharp angle and hitting a wall adjacent to the window.  If you can open the window to reduce lighting variations caused by the glass, all the better!  Here in the northern hemisphere, a south facing window often works well in the afternoon.  If the sun doesn't hit a wall, a palette, chair, or other object may be used to place your cardboard w/IT8 in the sun.

  4. Make sure the room is as dark as possible and that the only light entering the room is coming from the window.  Also try to avoid the direct sunlight hitting bright colored (non-neutral) surfaces such as red walls, blue floor tiles, etc. as these reflections can cause color shifts on the target.

  5. Place your target in the sunlight so that the sun is hitting the target at an angle and you can sit in the shadows while taking the shot.  The following is a typical setup for shooting an IT8 target in direct sunlight.  Notice how the sun hits the target at a sharp angle so that the camera can sit in the shadows, thereby eliminating glare on the target:

  6. If your camera has a custom white balance feature, using a white/gray card or a white sheet of copy paper (don't use photo paper with brighteners), place the card at about the same location as the IT8 and make sure it is in the sunlight.  Use the custom white balance on your camera to white balance on the card.

  7. Take several shots of the target in raw mode.  Take one "normal" shot and then increase exposure incrementally, taking several more shots with brighter exposures making sure to stop just before the exposure gets "blown out" in the highlights.  Camera settings like aperture usually have little influence, but smaller apertures often produce more even lighting across the frame.  Note that camera lens and ISO speed can make a slight difference in profiling, so be sure your ISO speed is set appropriately and you are using your most-often-used lens.  If you and/or the camera are sitting in the shadows of the room, you can take the photo straight-on at the target and you should get no glare or reflections.  When taking the photos, fill only about 3/4 of the frame with the target.  Don't zoom in so far that the target covers the entire frame because light falloff from the edges of the lens can be a factor here.

Once you have the shots of the target, turn off color management in your raw developing tool and develop the photos.  Depending on the raw tool you are using, turning off color management may entail selecting a color management tab and selecting "Embed camera profile", or selecting "None" in the "color management" dropdown.  Whatever you do, the important thing to remember is that you need to be able to turn off color management to develop the profile.  Then, once you are done creating the profile, the profile can be activated in the raw tool by selecting the ICC profile that you created.  Of course, this assumes that the raw tool you are using allows selection of custom profiles.  Not all tools allow use/application of custom profiles so be sure the tool you are using has this feature.  The more popular third party tools like Bibble, Capture One, and (the now discontinued) RawShooter allow the use of custom profiles.  When developing the images, develop to TIFF (you can use 8 or 16 bit/channel TIFF format).

In Profile Prism, click "File", "Open" and open one of the developed images of the IT8 target.  Next, make the following selections on the Profile Prism main window (description and file name are just an example):

Parameter Set to
Type of device to profile Camera/scanner
Reference target Choose the file for your IT8 target
Profile description Something like "Canon 5D Generic"
Printer target N/A
File name Choose a name like canon-5d.icm
Profile for Highest Accuracy
White balance Device dictates WB
Tone reprod. curves Gamma Match (Auto)
All other options "Normal" or zero (0)

The above parameters are appropriate for profiling a camera.  Once you have set all the parameters, mark the 4 corners of the target on the image of the IT8 target.  The step by step procedures for profiling a camera or scanner in the Profile Prism help will show you how and where to place the crop markers on the IT8 target.  Once placed, there should be a white punch-out in each of the color squares on the IT8 including the gray scale at the bottom.  If the punch-outs don't align inside each color square on the target, the corner markers have not been placed properly.  Finally, click "Create Profile" at the bottom left and Profile Prism will create your camera profile.  You can then test the profile by selecting the profile in your raw developing tool using the file name you used in the table above.  Once the new custom profile has been set, simply redevelop the photos and evaluate them for color accuracy/appearance.

Since some raw tools like Capture One and RawShooter apply some "pre-curves", it isn't possible to profile based on truly raw data.  As such, you may have to create a profile for each of the exposures (the one normal exposure and several brighter ones) and then pick the profile that has the tone curve (shadow and highlight detail) that you prefer.  Usually, the best result occurs when the curves displayed in Profile Prism (after clicking "Create Profile") end as close as possible to the upper/right corner of the graph.  If the curves end on the top edge or the right edge of the graph, you may need to try a different/better exposure.  Note that it is best to pick a different shot with a different exposure as opposed to tweaking the exposure of a single shot in the raw developing tool!  With a little practice, the above process can produce excellent profiles for any camera shooting in raw mode.  The above are the procedures we used to develop our own camera profiles for numerous raw tools.  These profiles have gotten many positive reviews and are often compared to profiles produced with much more expensive equipment/targets from other sources.


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.

Step 2: Open and crop the image of the target

  1. Click "File", "Open Image" and browse to the folder that contains the image of the reference target. Select one of the images and it will appear in the image crop area in the upper right of the window.

  2. Next, locate the upper/left edge of the 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.

  3. Next, click the upper left crop corner button.

  4. 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.

  5. 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.

  6. 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:

  7. Once all four corners of the 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.

  8. 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.

  9. Finally, review your messages. At this point, Profile Prism has examined the image of the target and has evaluated white balance, exposure, and lighting of the target. The details of this evaluation are displayed in the "Messages" box on the lower portion of the window. Here is a list of messages that are displayed at this point:

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.

Step 3: Generate the profile

Now it's time to sit back and let Profile Prism do its number crunching.

  1. Click the "Create Profile" button in the lower left corner.

  2. 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.

  3. 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.

  4. 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:

III. Utilizing Profiles Generated by Profile Prism

Note that the above instructions relate to generating an ICC profile for digital cameras. Since an ICC profile is a standardized method for describing how a camera records color information, using these profiles with images from your camera is a task left up to your 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