
Show HN: Paint Color Matching App (Sherwin, Behr, PPG) - jhiggins777
https://www.matchmypaintcolor.com
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crazygringo
I'm curious... if the RGB values are all accurate, is there a standard color
and exposure calibration for paint swatches that is shared across brands?

The white point (color temperature) is easy, using whatever light source
they're being illuminated with.

But what determines whether a particular white is (240, 240, 240) or (250,
250, 250) or (255, 255, 255)? The exposure seems far more arbitrary. Is there
some kind of maximally bright matte "reference white" material photographed
next to each swatch, that then gets calibrated to (255, 255, 255) or similar?

If so, it would be pretty cool if you could buy a reference white chip like
that, hold it up to a painted wall in your house, and have an app that could
take a photo with both and output the "true" current paint color.

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colanderman
You are thinking of a grey card:
[https://en.wikipedia.org/wiki/Gray_card](https://en.wikipedia.org/wiki/Gray_card)

However color matching is more complex than that. "Color of the light source"
varies considerably, not only due to the illuminant itself, but also the
materials the illuminant is reflecting off of (e.g. walls). And color
temperature only defines black bodies, which most light sources are not: you
need information about the full spectrum of the illuminant to determine how it
interacts with the material to be color-matched. This is getting a bit into
metamerism:
[https://en.wikipedia.org/wiki/Metamerism_(color)](https://en.wikipedia.org/wiki/Metamerism_\(color\))
(Of course, paint cannot match an arbitrary spectrum. Matching under specific
lighting conditions is the least you can hope for.)

And the above is considering color of a surface only as a scalar value, but
it's really a function of illumination angle as well, due to gloss. Direct
lighting on a glossy surface reflects more of the color of the gloss, whereas
oblique lighting reflects than the paint itself. Diffuse lighting is some
combination thereof.

(I am not a color scientist by any means, just interested in the topic.
Experts please correct!)

~~~
crazygringo
Ah ha, thanks! So turns out gray cards use "middle gray" which has both a
physical definition as well as a specific RGB value:

[https://en.wikipedia.org/wiki/Middle_gray](https://en.wikipedia.org/wiki/Middle_gray)

Fascinating. I never knew there was an "standard" mapping between real-world
colors and RGB.

Now if only online clothing store photos would map to that, so that the olive
green coat I order doesn't turn out to be closer to medium brown or vice-
versa... :P

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pkaye
I got one of those Color Muse color matching devices and this matching gets
hard when you have glossy or rough surfaces. I've been trying to get some
touchup paint to cover a stucco patch and despite many attempts, never can
match it close. The colors look different at various angles.

~~~
lttlrck
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.

~~~
mceachen
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.

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

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rafamvc
This doesn't have all Sherwin Williams colors. And the dropdown stops at the
letter B and after.

~~~
jhiggins777
The app actually does have all Sherwin Colors, they are just not all in the
dropdown (you can search for them). I added all of them in the dropdown for
now in a really janky way. I'll do a proper design in the next few days.

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ghostbrainalpha
What I want the ability to upload a picture of a paint chip, AND tell you how
long it has been since that wall was painted.

That way the app could adjust for fading and tell me what color that paint was
originally.

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tdy721
It's more variable than just time; and really if you aren't matching the
color, just pick one you like?

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mjgoeke
Something is off. The matched colors show an RGB with each, but it's the same
value when the color is obviously different. I took a screenshot of it and
pulled it up in an image editor to make sure.

e.g. [https://www.matchmypaintcolor.com/ppg/medieval-
forest](https://www.matchmypaintcolor.com/ppg/medieval-forest) shows RGB
1,116,120 for all 3 swatches, but only the Maxi Teal is that RGB, the other
tiles have other RGB values.

~~~
jhiggins777
Thanks mjgoeke, all fixed.

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gitgud
This looks exactly like one of those "Buy this domain" place holder sites.

Compare the pair:

\- [https://www.matchmypaintcolor.com/](https://www.matchmypaintcolor.com/)
(this site)

\- [http://surfweb.com/](http://surfweb.com/) (fake site)

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jamesrom
How do you calculate the distance between these colors? RGB distance will be
close enough, probably, but for matching paint/ink in the real world, it's
important to consider visual (sensation) difference.

[https://en.wikipedia.org/wiki/Color_difference](https://en.wikipedia.org/wiki/Color_difference)

~~~
jhiggins777
[https://github.com/dtao/nearest-color](https://github.com/dtao/nearest-color)

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rkho
Oh this is fun. I recently paid $4.99 to unlock similar functionality with a
different webapp, though that one also supported Kelly Moore and others.

Any intentions on adding suggested palettes?

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lttlrck
I would love to be able to match by RGB.

Edit: actually it’s almost possible to do what I need. It’s just be much
easier if it was possible to find closest match. Still this could be helpful.

~~~
andytruett
I've used the following to match RGB and HTML color codes to paint colors:
[http://www.easyrgb.com/en/match.php](http://www.easyrgb.com/en/match.php).
Wasn't perfect, but got me pretty close!

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bradknowles
I have a Pantone CapSure color sampling/matching device, which includes a wide
variety of color samples from various manufacturers.

Any idea how this process compares?

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swframe2
I'm curious. What is the algorithm to determine how to mix paints to match a
color?

~~~
jhiggins777
[https://github.com/dtao/nearest-color](https://github.com/dtao/nearest-color)

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kube-system
I need this but for automotive paints

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markdown
> PPG, Behr, & Sherwin Williams

What are these? The website doesn't seem to explain anywhere.

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jhiggins777
The major paint manufacturers.

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markdown
Ahh ok, thanks. Must be American. Never heard of them in my part of the world.

