4 ms·

On light, colors, mixing paints, and numerical optimization

190 points by ibobev 3y ago

sagebird 3y ago
This is a lovely exploration of color. Thank you for sharing.
sdenton4 3y ago
Absolutely love this. I've been getting into mixing for miniature painting myself, but with a bit of added perspective which (I think) isn't captured here. It turns out there's more than just raw color going on here. Acrylic paints have different degrees of opacity, and you can increase transparency by mixing in acrylic medium. Additionally, adding water and/or flow-improver helps the acrylics slide off flat surfaces into crevices, producing deeper colors in recesses and thinner applications in open areas - this is the principle which gives us washes, shades, and contrast/speed paints. And there's basic acrylic mediums (matte or gloss) but also specialty mediums which have more texture (gels, modeling pastes) or additives (pumice, fiber, glass micro-beads). [Edit: And of course, Metallics!!! There's a few different additives, like mica, which are used to create metallic paints.] Together, this points to a combinatorial problem: No pre-mixed bottles will ever cover all of the possibilities, so you have to start mixing paints (and mediums!) to achieve the desired effects in any particular project.
- raphlinus 3y ago
  Indeed. I learned color theory from "The Measurement of Appearance" by Richards Hunter and Harold, and one of the strengths of that work is that goes well beyond simple color into things like gloss, opalescence, etc. Highly recommended. Also Bruce MacEvoy's in-progress book "Color Experience"[1] looks like it will be a fairly definitive treatment of the topic. It is also rooted in physical colorants (the author is an extremely serious watercolorist). [1]: https://www.handprint.com/CE/book.html https://www.handprint.com/CE/book.html
- gilleain 3y ago
  I've been using various paints (watercolour, gouache, acrylic) and various mediums (gum arabic, aquapasto, gloss gel medium) on (paper, canvas, gesso) to paint repeating patterns. It's interesting how much experimentation you have to do to learn about a particular paint or combination of paint and medium. Sometimes I think combinations will have _more_ of an effect - I was hopeful that ink on paper below gloss medium acrylic would be more obvious, but did not come out the way I expected.
dt23 3y ago
Such a nice surprisingly thorough overview (nice diagrams too!)
oluckyman 3y ago
Nice description! For project of this type that has been going for 20 years, and covers many different paint sets, see https://zsolt-kovacs.unibs.it/colormixingtools https://zsolt-kovacs.unibs.it/colormixingtools
itronitron 3y ago
Nice write up from a technical/engineering perspective however it has some notable gaps on the color 'perception' side.
fjfaase 3y ago
I know an artist who is an expert of mixing colors and lightning. He spend his whole life mixing colors. In the past decades he created several color palettes to be use inside and/or outside buildings [1]. In 2013 and 2014 he created 21 works (consisting of pairs of paintings) that contain color palettes experimenting with variations of brightness and saturation of six evenly passed colors [2]. In 2020/2021, he created eight works with color palettes existing of twelve even passed colors with the same brightness and saturation (by daylight) [3]. He complains a lot about lightning in museums, that it deviates a lot from daylight, while many works of art are create by daylight. The light is often too yellow, based on some 'dubious' research that museum visitors prefer yellow light. LED lightning often causes mixtures of pigments that look the same under daylight to look different under LED lightning. LED lightning often is rather weak in the infra-red to red part of the spectrum cause most reds in painting to fade. He found a combination of a reddish and a blue TL-lamps supporting to LED lights to give a better approximation of daylight. When this was applied to some museum rooms, the son of a man who donated a work, asked what they did with it work as it looked again like how it looked at their home when it was hung close to the windows. (Shortly after this the museum director decided to use only LED lightning for the new wing that was going to be build.) The problem of course is that we are so used to adapt our color vision to the lightning that most people do not see the difference. I guess that people who mix colors all the time, develop some kind of absolute color vision and do notice the effect of improper lightning on art works. [1] https://www.pstruycken.nl/EnDyn.html?Li,tag=q&w https://www.pstruycken.nl/EnDyn.html?Li,tag=q&w [2] https://www.pstruycken.nl/EnS14.html https://www.pstruycken.nl/EnS14.html [3] https://www.pstruycken.nl/EnS20.html https://www.pstruycken.nl/EnS20.html
- enriquto 3y ago
  > LED lightning often causes mixtures of pigments that look the same under daylight to look different under LED lightning. I'm surprised that this extremely cool phenomenon is not embraced by artists and exploited as an essential part of their language. For example, they could use pigments with bizarre absorption spectra/fluorescent properties, so that the same painting looks completely different when put near a sunny window or under a led lamp. Focusing only on color rendering under daylight seems a bit short-sighted, now that we master all sorts of synthetic lighting and fancy chemistry.
tslater2006 3y ago
What a wonderful and detailed wrote up. Thank you for this! I wrote something similar but never released it due to not having a lot of hobby paint colors to include. It uses LAB for linear distance as a scoring mechanism and reflectance curves from RGB for the mixing. And a genetic algorithm for finding a recipe. Here's a short video of an older version. Newer one let's you set how long to search for. https://youtu.be/eGgrowt1fWg?si=NwucIgfpeWpbmCPX https://youtu.be/eGgrowt1fWg?si=NwucIgfpeWpbmCPX
xeonmc 3y ago
Light is therefore color, and shadow the privation of it by the removal of these rays of color, or subduction of power; and these are to be found throughout nature in the ruling principles of diurnal variations. The grey dawn, the yellow morning and red departing ray, in every changing combinations, are constantly found to be by subduction or inversion of the the rays of their tangents. -- J. M. W. Turner, 1818. https://archive.org/details/colourinturnerpo0000gage/page/110/mode/2up?q=%22light+is+therefore+color%22 https://archive.org/details/colourinturnerpo0000gage/page/11...
- jjgreen 3y ago
  Colours are the deeds of light; its deeds and sufferings: thus considered we may expect from them some explanation respecting light itself. J. W. Goethe, preface to The Theory of Colour, 1810
flobosg 3y ago
The article reminded me of Mixbox (https://scrtwpns.com/mixbox/ https://scrtwpns.com/mixbox/), which implements pigment-like mixing of colors aimed at digital painting.
mbivert 3y ago
As a painter, this is both amusing and terrifying to read. There are simple ways to conceptualize color mixing, for example the primary model, or HSV. Of course, those are models, so they don't capture everything, as mentioned ITT (e.g. transparency, lightfastness, texture, potency, price) but they're practically good enough. For example, in a primary (+white) setting, a given mix can only: - not have enough red - not have enough blue - not have enough yellow - not have enough white So the only questions one can ask is: "does it need more red/yellow/blue/white?", period. If one has more than those 4 colors, then the trick is to understand them in terms of red/blue/yellow/white: one is then left again with those 4 questions. I've found HSV more practical than RYB, but people are generally accustomed to RYB, hence why I've described it instead; the general idea really is the same: only a small, finite number of mistakes. It's simple, but it still requires a few hours of practice until it becomes intuitive, especially with "real world" pigments.

190 points by ibobev 3y ago

This is a lovely exploration of color. Thank you for sharing.

Absolutely love this. I've been getting into mixing for miniature painting myself, but with a bit of added perspective which (I think) isn't captured here. It turns out there's more than just raw color going on here. Acrylic paints have different degrees of opacity, and you can increase transparency by mixing in acrylic medium. Additionally, adding water and/or flow-improver helps the acrylics slide off flat surfaces into crevices, producing deeper colors in recesses and thinner applications in open areas - this is the principle which gives us washes, shades, and contrast/speed paints. And there's basic acrylic mediums (matte or gloss) but also specialty mediums which have more texture (gels, modeling pastes) or additives (pumice, fiber, glass micro-beads). [Edit: And of course, Metallics!!! There's a few different additives, like mica, which are used to create metallic paints.] Together, this points to a combinatorial problem: No pre-mixed bottles will ever cover all of the possibilities, so you have to start mixing paints (and mediums!) to achieve the desired effects in any particular project.

raphlinus 3y ago
Indeed. I learned color theory from "The Measurement of Appearance" by Richards Hunter and Harold, and one of the strengths of that work is that goes well beyond simple color into things like gloss, opalescence, etc. Highly recommended. Also Bruce MacEvoy's in-progress book "Color Experience"[1] looks like it will be a fairly definitive treatment of the topic. It is also rooted in physical colorants (the author is an extremely serious watercolorist). [1]: https://www.handprint.com/CE/book.html https://www.handprint.com/CE/book.html
gilleain 3y ago
I've been using various paints (watercolour, gouache, acrylic) and various mediums (gum arabic, aquapasto, gloss gel medium) on (paper, canvas, gesso) to paint repeating patterns. It's interesting how much experimentation you have to do to learn about a particular paint or combination of paint and medium. Sometimes I think combinations will have _more_ of an effect - I was hopeful that ink on paper below gloss medium acrylic would be more obvious, but did not come out the way I expected.

dt23 3y ago

Such a nice surprisingly thorough overview (nice diagrams too!)

oluckyman 3y ago

Nice description! For project of this type that has been going for 20 years, and covers many different paint sets, see https://zsolt-kovacs.unibs.it/colormixingtools https://zsolt-kovacs.unibs.it/colormixingtools

itronitron 3y ago

Nice write up from a technical/engineering perspective however it has some notable gaps on the color 'perception' side.

fjfaase 3y ago

I know an artist who is an expert of mixing colors and lightning. He spend his whole life mixing colors. In the past decades he created several color palettes to be use inside and/or outside buildings [1]. In 2013 and 2014 he created 21 works (consisting of pairs of paintings) that contain color palettes experimenting with variations of brightness and saturation of six evenly passed colors [2]. In 2020/2021, he created eight works with color palettes existing of twelve even passed colors with the same brightness and saturation (by daylight) [3]. He complains a lot about lightning in museums, that it deviates a lot from daylight, while many works of art are create by daylight. The light is often too yellow, based on some 'dubious' research that museum visitors prefer yellow light. LED lightning often causes mixtures of pigments that look the same under daylight to look different under LED lightning. LED lightning often is rather weak in the infra-red to red part of the spectrum cause most reds in painting to fade. He found a combination of a reddish and a blue TL-lamps supporting to LED lights to give a better approximation of daylight. When this was applied to some museum rooms, the son of a man who donated a work, asked what they did with it work as it looked again like how it looked at their home when it was hung close to the windows. (Shortly after this the museum director decided to use only LED lightning for the new wing that was going to be build.) The problem of course is that we are so used to adapt our color vision to the lightning that most people do not see the difference. I guess that people who mix colors all the time, develop some kind of absolute color vision and do notice the effect of improper lightning on art works. [1] https://www.pstruycken.nl/EnDyn.html?Li,tag=q&w https://www.pstruycken.nl/EnDyn.html?Li,tag=q&w [2] https://www.pstruycken.nl/EnS14.html https://www.pstruycken.nl/EnS14.html [3] https://www.pstruycken.nl/EnS20.html https://www.pstruycken.nl/EnS20.html

enriquto 3y ago
> LED lightning often causes mixtures of pigments that look the same under daylight to look different under LED lightning. I'm surprised that this extremely cool phenomenon is not embraced by artists and exploited as an essential part of their language. For example, they could use pigments with bizarre absorption spectra/fluorescent properties, so that the same painting looks completely different when put near a sunny window or under a led lamp. Focusing only on color rendering under daylight seems a bit short-sighted, now that we master all sorts of synthetic lighting and fancy chemistry.

tslater2006 3y ago

What a wonderful and detailed wrote up. Thank you for this! I wrote something similar but never released it due to not having a lot of hobby paint colors to include. It uses LAB for linear distance as a scoring mechanism and reflectance curves from RGB for the mixing. And a genetic algorithm for finding a recipe. Here's a short video of an older version. Newer one let's you set how long to search for. https://youtu.be/eGgrowt1fWg?si=NwucIgfpeWpbmCPX https://youtu.be/eGgrowt1fWg?si=NwucIgfpeWpbmCPX

xeonmc 3y ago

Light is therefore color, and shadow the privation of it by the removal of these rays of color, or subduction of power; and these are to be found throughout nature in the ruling principles of diurnal variations. The grey dawn, the yellow morning and red departing ray, in every changing combinations, are constantly found to be by subduction or inversion of the the rays of their tangents. -- J. M. W. Turner, 1818. https://archive.org/details/colourinturnerpo0000gage/page/110/mode/2up?q=%22light+is+therefore+color%22 https://archive.org/details/colourinturnerpo0000gage/page/11...

jjgreen 3y ago
Colours are the deeds of light; its deeds and sufferings: thus considered we may expect from them some explanation respecting light itself. J. W. Goethe, preface to The Theory of Colour, 1810

flobosg 3y ago

The article reminded me of Mixbox (https://scrtwpns.com/mixbox/ https://scrtwpns.com/mixbox/), which implements pigment-like mixing of colors aimed at digital painting.

mbivert 3y ago

As a painter, this is both amusing and terrifying to read. There are simple ways to conceptualize color mixing, for example the primary model, or HSV. Of course, those are models, so they don't capture everything, as mentioned ITT (e.g. transparency, lightfastness, texture, potency, price) but they're practically good enough. For example, in a primary (+white) setting, a given mix can only: - not have enough red - not have enough blue - not have enough yellow - not have enough white So the only questions one can ask is: "does it need more red/yellow/blue/white?", period. If one has more than those 4 colors, then the trick is to understand them in terms of red/blue/yellow/white: one is then left again with those 4 questions. I've found HSV more practical than RYB, but people are generally accustomed to RYB, hence why I've described it instead; the general idea really is the same: only a small, finite number of mistakes. It's simple, but it still requires a few hours of practice until it becomes intuitive, especially with "real world" pigments.