ImageMapper: Image Quality FAQ's
 Where is the best location to place the ColorChecker in the scene that I’m shooting?
 The ColorChecker should be placed in a scene location that receives the main lighting intended for the critical subject that you are photographing. It should also be located at a distance from the camera that is approximately the same as the subject. The lighting should be even and diffuse.
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What is the best lighting for building a digital camera profile?
Soft diffuse lighting, so the ColorChecker and main subject receive the same exposure, is ideal. Indirect daylight and studio lighting produce the best results. More contrasty lighting can produce good profiles if care is given to position the ColorChecker in the main lighting. Good results are possible, for instance, when a person is standing in direct sunlight with the ColorChecker held directly in front of them and deep shadows fall behind the person. As long as the direct light falls both on the ColorChecker and the subject the profile will work well.
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What is the best exposure for building digital camera profile?
Profiling will work best if the diffuse white patch on the ColorChecker (the bottom row, white patch) is the brightest white with detail in the scene. For instance, if the main subject is a white bridal gown, the ColorChecker white patch should be either the same brightness or somewhat brighter then the white gown. This is because the white patch is designed to represent the brightest white with detail, such as white fabric. Specular highlights, or whites without detail are much brighter than diffuse white and will be correctly reproduced when the diffuse white patch is correctly exposed.
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What does it mean if I get the message “The profile has been built but may not have the highest quality”?
This message often simply means that the tolerances that are built into the program that define a “statistically good” profile have been exceeded. This does not necessarily mean that you have built a “bad-looking” profile. Profiles that are slightly outside the tolerances for the program may look fine to the human eye – only you can be the judge.
There are cases, however, when this message can signal a significant problem with your capture. Digital photography is more like shooting traditional transparency film than shooting traditional color negative film – that is, there’s less tolerance for over and underexposures. For example, highlight detail lost due to overexposure cannot be retrieved; the same is true for shadow detail lost through underexposure.
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How can I check the severity of the problem if I see this message?
If you get the above message, click Details… to view the statistics for your input profile. Scroll until you can view the R, G and B (red, green, blue) values for patches D1 through D6 (look in the “Label” column to see these patch names). These patches are the 6 neutral patches that run along the bottom of the ColorChecker target, from lightest to darkest.
Over-Exposure: If patches D1 and D2 have RGB values that are high and close together, this indicates an overexposed capture. An extreme example would be if both patches read 255 in R, G or B., In this case, the profile will likely make the image worse; therefore, we recommend another capture session to avoid highlight reproduction issues.
Under-exposure: If patches D5 and D6 have very low values and are close together, that can indicate underexposure and loss of shadow detail.
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Checking the ImageMapper statistics seems a little complex, and it’s late in the process to discover that my exposures aren’t right. Can I do more up front?
Yes. The capture stage is always the preferred time to adjust exposure; it’s early in the process, and the subject and lighting are still available.
Some professional-grade camera display some visual warning of blown-out highlights when you view the capture on the camera’s LCD display. The blown-out highlights may glow a unique color like red or green, to give you a quick visual check for exposure.
Along with this white point alarm, professional cameras often also allow you to view a histogram on the camera’s LCD. Learning to judge a histogram for indication of over and underexposure can be an invaluable tool.
Bottom line: set the lighting evenly and as diffuse as possible, and set the exposure “safely” (highlights not clipped, shadows not plugged). Within this range, the ImageMapper profile will take care of tone and color rendering to the aim established by the selected Look profile.
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Can I use third-party software to check for reasonable exposure before I create my profile?
Yes. Open the image containing the ColorChecker target in an imaging application that allows you to read RGB values, like Adobe Photoshop, your camera’s “acquire” program, Breeze Browser or Bibble. Use the software’s readout function (such as Photoshop’s Info window) along with your own visual inspection.
- Check to see that the whitest neutral patch of the ColorChecker does not have red, green or blue values exceeding 250
- Visually confirm that shadow areas of the picture have detail, and that you can distinguish among the neutral patches of the ColorChecker
- Check that colored patches of the Color Checker are not overly saturated; generally they should not be above 250 in the highest channel
- Check that the lowest of the red, green and blue values in the darkest neutral ColorChecker patch is no less than 5
- Check that red, green or blue values are not 255 or 0 in any of the patches
- Check that each of the RGB values for the colored patches is higher than the values for the darkest neutral patch
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What if the ColorChecker is placed out-of-square in the test shot?
The Input Profile assistant is quite tolerant of “horizoning” error in the placement of the ColorChecker. The ColorChecker need not be perfectly square in the capture.
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Any other recommendations regarding the target as it affect image quality?
Here are a few:
- Place the ColorChecker in the scene so that you can see all parts of the chart; make sure other objects don’t obscure the patches
- Use Daylight or Strobe (D5000) as the main lighting source to light the ColorChecker. Be sure that the light falls evenly over the chart.
- The ColorChecker itself need not take up a large portion of the frame in the test shot, but make sure it is large enough to be usable by the software. In the test shot, it should be 200 pixels or wider.
- Shoot the scene with the same exposure and ISO settings that you’ll use for subsequent shots
- Again—even, diffuse lighting works best. Very “contrasty” lighting, such as direct sunlight or a single direct flash may not be suitable for profile building.
- When you draw a box around the ColorChecker in the ImageMapper software, make it a loose box—it’s not necessary to draw a tight box.
- Use care not to cut out all or a part of the ColorChecker when you draw the box
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Can I continue to use a profile that I made if the lighting changes/is changed?
When you make a profile for your camera, that profile optimizes your capture for the lighting and exposure conditions that were used when you made the test shot containing the target. That profile should yield good results for subsequent shots made under the same conditions.
Within limits, slight repositioning of studio lights should not change the quality or usability of your initial profile. The lens, camera, lighting units and surround play a big part in image quality. For example, in the case of food shots, which are typically lit from behind, you can move the main lighting to the front, build the profile, and then move the light to the rear position, and the profile should still work. However, if you change, for example, your lens, or the diffuser over your strobe, all bets are off.
As a general rule, you should re-profile when the lighting changes in a significant way, or when changes are made to lens, camera, lighting units or anything in the surrounding environment that affects ambient light.
Note: If you want to set up lighting to create a particular “mood”, such as an amber cast over the scene, we recommend first establishing the main lighting without the mood lighting, and capturing the target for profile building. Then add the mood lighting elements, recapture the ColorChecker as a second reference, and shoot the scene(s) per the customer specifications. Adventurous imaging specialists might choose to merge the two captures in Photoshop at a visually acceptable opacity level, save the new target image, and use ImageMapper as usual to convert the folder.
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How do the settings in ImageMapper preferences affect the color reproduction?
The first thing you should do is to choose the camera’s nominal export color space as the default input profile. Most cameras export SRGB files, which are limited in gamut, but many vendors are starting to offer support for Adobe (1998). For professional print production, we recommend that you choose Adobe (1998) if your camera software supports it.
The second (more important) selection is the Look profile. ImageMapper delivers a reference set of Look profiles based upon professional photography systems. The default look is designed to deliver reasonable results in both people and products; this requires a good neutral balance, pleasing flesh-tones, and clean and bright reproduction of saturated colors.
The Portrait Look is designed to deliver safe, desaturated results in fleshtones. Flesh-to-neutral balance is emphasized, and colors are more muted (less saturated) than with most other Looks. The Portrait Lab look is the sole exception.
The Chrome Type1 and Type2 Look profiles simulate the appearance of Ektachrome and Kodachrome respectively. These Looks create rich colors, with darker 3/4 tone to shadow values than other Looks. The shadow detail is retained as much as possible, but is considerably darker than other Looks, to simulate the higher density range of chrome relative to reflective prints.
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What is the difference in RGB working spaces and why choose one over the other?
Apple RGB- This is the old Apple 13 inch monitor standard it was used in early Photoshop as editing space so legacy files might have this profile.
sRGB- sRGB IEC-61966-2.1 considered a multipurpose working space more for consumer cameras to better match inkjet and color monitors closer. Ideal working space for the web but not for repro work as it clips the CMYK gamut especially in the cyan region.
ColorMatch RGB- This is an open standard monitor RGB color space 1.8 gamma, a known legacy standard for archived Photoshop files.
ProPhotoRGB- This color space has a large gamut and is intended for images that will be output on photographic devices for transparencies or to take advantage of the wider ink jet space. Editing should be bone in 16 bit mode so as not to loose the advantage of the wide color space.
Adobe RGB (1998)- This is the recommended editing color space for RGB files, especially if files are to be used for printing in CMYK space. This is the color space that is used in Photoshop’s U.S. Prepress Defaults in the Color Settings set-up window.
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Can I make a profile using my cameras on-board “pop-up” flash?
Very small flashes tend to create hot spots in the middle of the image. This can cause the exposure on the ColorChecker to be very different than on the main subject, even if the subject is a person’s face just above the target. If after making the profile, the target looks good but the face is much too dark, or even too bright, try moving the camera further back so the light is more evenly distributed across the entire scene and the face and target have the same exposure.
Another common profiling problem occurs when a person hold the ColorChecker out towards the camera so the target is overexposed. Try holding the target just in front of the subjects face so the exposure on the face and the target are the same.
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Who do I contact for comments and suggestions?
Send email to: ColorCFSsupport@kpgraphics.com
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