Unexpected results from Export Color List?


I’m running ColorThink 2.2.1b5 on OS X 10.6.3. I’m trying to create a color list that I can look at in a spread sheet so I can see what Argyll is doing when generating patches. The first attempt I noticed that there were a lot more colors than there really were (this is a 1728 patch target) so I took a closer look and noticed that there is a 1 pixel transition between some, but not all of the patches. I used a fixed size marquee in Photoshop to delete those transitions and tried again but still I’m getting very unusual results. In the spreadsheet I’ve sorted by ascending R,G,B values and have filtered out the duplicates. I should in theory have 1728 discrete colors but it’s showing 4200 discrete values. (I generated a generic target using targen -v -d2 -G test1728, and printtarg -v -iSS -pA4R -t test1728). The target definitely only has 1728 different colors in it.

I also tried this on a target which was generated by Monaco Profiler. MP is generating predictable evenly distributed patches. You can see some of that yet the color list is showing FAR more colors than are actually there in the target.

As a test I created a file that was 1200x800 pixels. I filled 400 pixel increments with red, green and blue respectively, saved and then extracted the colors. What I would expect would be 6600 samples but only 3 different colors that were 255,0,0; 0,255,0; and 0,0,255. What I ended up with (after filtering out the duplicates) was:


I guess I expected that “export color list” would generate a list of every discrete color in an image. I guess in a regular photograph that might be impractical as that could be quite a large number so after thinking about it for a while… it seems as if it may be just taking samples at some pre-determined x,y spacing but with an aperture that’s larger than 1 pixel and this is why I’m seeing more than 3 colors in this particular test.

Would that be accurate?

Cheers, Joe

Hi Joe,

You have the general idea, but the software goes about it a little differently.

ColorThink 2 automatically downsamples most images to bring them into a more workable size. (That’s the equivalent of your larger aperture analogy.) Then we extract the colors from that. This function was designed to be a quick and easy way to create a color list that is representative of an image in a size that would be manageable for graphing.

Many of the color geeks in the industry wanted a more precise way to sample colors from a target like you’re doing, so when we were putting together ColorThink Pro, we added the marquee tool to the Worksheet. There you have built-in the grid patterns of several common testcharts, and you have the option of creating your own custom target marquee by specifying the number of columns and rows you need.

There is more detail on how the Target Marquee tool works in the ColorWiki manual:

There’s not a lot there in terms of screenshots of the Marquee tool, but now that you brought this subject up, I’ll see if I can get some time this week to put a few illustrations in there so people can see how it works.

Thank you so much Patrick…

I’ll definitely be upgrading to pro then, there’s a few more specific applications (beyond reverse engineering other targets) which would be very useful to me when I need to extract specific colors for generating targets.

Cheers, Joe