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Comment by lttlrck | Hacker News Reader

I have the same problem. My current plan is to illuminate a patch from many angles to eliminate all the shadows. Add a reference white or gray card. Take a photo then in GIMP, adjust the white point, blur the stucco, read off the RGB and look up the closest matching color code. I have yet to find a way to look up by RGB.

If it somehow works I’ll avoid having to paint the whole house.

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The colorimeter at your local paint store, looking at a paint chip from your wall, is very likely going to do a whole lot better than the process you just described. If you call the store, ask how big of a paint chip sample they need to match existing, weathered paint. It very well may be tiny (like, 1cm^2), and they should do this color match for free. You could buy just a pint, first, to see that it works.

I've been quite surprised by how non-uniform most digital camera imagers and in-body post processing color pipelines muck with the spectrum coming off the sensor, all in the name of producing a more pleasing JPEG. If you still want to do what you described, I'd use RAW and use dcraw to convert to tiff, and open that in gimp.

What they have in-store is most likely a spectrophotometer, not a colorimeter.

Your best bet is to cut a piece of paint off the wall and take it to a paint store. They probably won’t be able to match it exactly, but it’ll be closer than you can do in RGB.

If you’re concerned about a close match, this is unlikely to give satisfactory results.

Take your samples to a good paint store. Those machines are more sophisticated then you may think.

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