How to get true color of an object

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strantor

Joined Oct 3, 2010
5,967
I am trying to match a specific color by mixing paints, and I think this is something intuitive for most people, or maybe just artists, but for me nothing has changed since kindergarten and all my color mixes eventually trend toward turd brown. I have an app on my phone that lets you decompose a color into its parts, very handy, especially in that you can tell it what colors you have available, and it will tell you the proportions in which to mix them, to get as close to the target as possible. This seemed like the silver bullet so I paid out for the full version of the app and it does as advertised but the problem is, when I take a picture of the thing I want to color match and I hover the color picker cursor over it, depending on where on the object I hover (in shadow, in reflection, or anywhere in the gradient between) it will report one of dozens or hundreds of color codes. I can pick a spot on the picture that I think best represents the actual color but it's not perfect. Then I must do the same thing (snap picture, color picker cursor, imperfect selection) for each color of paints I have. Then I decompose the color into the colors I have and mix in the prescribed ratios, and the result isn't even close. I assume the imperfections in my selections are compounding and skewing the result wildly. And/or that actual paints do not mix in the real world in the ideal way that they should according to the math; maybe the physical properties of some pigments make them "weaker" or "stronger" than their digital representations suggest. But that is something I think I can only confirm after I've eliminated the error in my color selections. So that is my question. How can I eliminate the color gradient caused by ambient light and take a picture or otherwise sample the true color of an object?
 

Ya’akov

Joined Jan 27, 2019
5,659
To get an accurate match you need a good light source with three attributes:

1) Shadow free lighting, the is usually accomplished with a soft box larger than the object. It sometimes takes two. There are competing requirements for a good photo versus a good color match. The lighting for a good photo controls but maintains the shadows while pure color matching wants uniform, shadowless lighting.

2) A CRI (Color Rendering Index) ≥ 90. The CRI determines the gamut you will be able to see.

3) A color temperature of 5000K. This is the standard for color matching.
 

GetDeviceInfo

Joined Jun 7, 2009
2,095
you may want to touch base with the specific paint manufacturer and see what they say. Back in my flexographic printing days, we used a specific inking system and no other ink would perform at any level that was close to replicating a match.
 

MrSalts

Joined Apr 2, 2020
1,762
To get an accurate match you need a good light source with three attributes:

1) Shadow free lighting, the is usually accomplished with a soft box larger than the object. It sometimes takes two. There are competing requirements for a good photo versus a good color match. The lighting for a good photo controls but maintains the shadows while pure color matching wants uniform, shadowless lighting.

2) A CRI (Color Rendering Index) ≥ 90. The CRI determines the gamut you will be able to see.

3) A color temperature of 5000K. This is the standard for color matching.
5000K is occasionally used but but most automotive companies use 6500K for color matching. X-rite/Pantone light boxes are available in both 5000K and 6500K bulbs and 2300K for interior tungsten color matching.

Particle size and opacity of pigment is key - you'll never get the right mixing intensity if you are using blue dyes and red pigments. Dyes and pigments are very different. There is so much more to color matching. An iPhone app will not do it. There is a reason that an X-rite surface spectrophotometer is more than a $700 iPhone. They have been refining surface color matching since the early 1990s.
 
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