[10.24.2001]
Interview with Robin Myers: Part 3
Robin: All the commonly available tools for working with spectra are targeted for designers. They have very nice interfaces for selecting colors from swatchbooks or choosing color schemes. SpectraShop™ is a toolkit for the color scientist who is interested in acquiring not only the spectra of a color, but all the associated data that makes it possible to do a wide variety of analyses. As examples of its applications, I have used SpectraShop™ to determine aim values for color targets, perform fluorescence analysis, create paint matches, make metamerism studies, analyze digital camera performance, evaluate lighting, investigate flower pollen targets and many more purposes. It has become my main spectral acquisition and analysis tool. It works directly with the GretagMacbeth Spectrolino, and can import data from many other instruments.
Jeff: What ICC profiling software do you prefer to use these days? Why?
Robin: I work with several packages and I'm right in the middle of testing some of the more popular programs. I'll hold back comment on what I recommend until the testing is complete.
Jeff: I know you're deeply involved in digital photography now, particularly with your association with Better Light. What do you see as the particular challenges to profiling digital cameras?
Robin: Digital camera profiling is actually quite easy, if you look at it the right way. There are only three types of digital photography shooting situations; reproduction, artistic and automatic. Reproduction photography is where the image on the computer screen and print must match the original object as precisely as possible. Examples of this situation would be fine art reproduction and product photography. This situation corresponds to a colorimetric rendering intent. To profile this situation, place a color target in the scene, capture an image using the same conditions as the final image, create a profile and attach it to the image.
Artistic photography is widely practiced in professional photography where the exposure conditions such as lighting, tone processing curve, colored filters, etc., are adjusted until the image matches the artistic vision of the photographer or art director, but it almost never matches the original objects. Since the screen image is the desired image, the monitor profile should be attached to the final image for subsequent processing.
Automatic photography is the situation where the camera is making all the exposure decisions based on it's interpretation of the scene and it's built-in processing. This is a common occurrence with consumer digital cameras. The situation is analogous to a perceptual rendering intent. The image does not necessarily match the original objects, but a pleasing picture is produced by the camera. For this situation, the camera manufacturer usually provides a default profile, or some cameras are set to deliver the image in an sRGB color space, so the default or sRGB profile should be used.
Jeff: Can you comment on the ColorChecker DC?
Robin: The ColorChecker DC is the first widely available camera target designed for calibrating and profiling digital cameras. I give GretagMacbeth high marks for taking the first step in providing a target for these purposes. The concept is very good, but there are some problems with the implementation. One problem is with the glossy patches on the target. They act as nice little mirrors, reflecting everything in front of the target back to the camera. Unless the target is placed into a reflection-controlled environment, these reflections will ruin any profile made with the target. So most software has to ignore them, making them useless and a waste of precious target space.
Also, it has recently been discovered that many of the patches on the target polarize their reflected light. When the ColorChecker DC is used to create ICC profiles for extremely color accurate fine art reproduction, these polarizing patches produce profiles that ruin the reproduction. This is especially noticed when photographing oil paintings since a cross- polarized light setup is required to eliminate reflections from the painting. I have seen some gray patches turn darker than the black patch when the target is illuminated by polarized light. So, it is a good first try, but GretagMacbeth needs to continue its development and come out with an improved ColorChecker DC. However, if you are not using polarized light, I recommend its use.
Jeff: All right, let's talk about the future — what trends you see evolving and what you'd like to see happen. For one, how would you like to see color management evolve? ColorSync?
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