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What’s the difference between chroma and saturation?

In the Mun­sell color sys­tem, and in paint­ing gen­er­ally, the word for color inten­sity is “chroma.” Another word that means almost the same thing is “sat­u­ra­tion.” Sat­u­ra­tion is com­monly used in com­puter graph­ics to describe color inten­sity. They don’t have quite the same meaning.

Sat­u­ra­tion runs on the same scale (often 1100) regard­less of the hue or the value. So the most intense blue, no mat­ter what, is a sat­u­ra­tion of 100. The most intense yel­low, sim­i­larly, has a sat­u­ra­tion of 100. That’s very con­ve­nient for peo­ple who design soft­ware inter­faces. And if you don’t really under­stand color, it makes per­fect sense. What it doesn’t do is model color accurately.

In real­ity, the most intense yel­low is far more intense than the most intense blue. And the high­est pos­si­ble inten­sity varies depend­ing on how light or dark the color is. The most intense yel­lows are found at a rel­a­tively light value. The most intense blues occur at some­what darker val­ues. At very high and very low val­ues, max­i­mum chroma goes way down. But you can always set the sat­u­ra­tion to 100 to get the most intense color at the hue and value you have cur­rently selected.

Chroma runs on a dif­fer­ent scale. In Mun­sell, the most intense chroma for yel­low runs up to about 18. The most intense blue is more like 12. (I’m doing this from mem­ory, so these num­bers might be a lit­tle off.) Those num­bers change with hue and value, so that the Mun­sell color space is an irreg­u­lar, lumpy cylin­der. That is a much more accu­rate depic­tion of human color vision than the sat­u­ra­tion model. It helps to think about color in this way when you’re try­ing to under­stand actual color relationships.

Update and Correction

28 Feb­ru­ary 2008:

David Briggs, in com­ments to this post, writes:

To clar­ify, David, my objec­tion is that you seem to be judg­ing sat­u­ra­tion as if it was meant to be a mea­sure of colour inten­sity. It isn’t, it’s a mea­sure of colour purity. The term for inten­sity of colour of light is “col­or­ful­ness”, the prod­uct of the sat­u­ra­tion of a light stim­u­lus and its brightness.

Many colours reflect light of high sat­u­ra­tion, but only those that reflect light of high col­or­ful­ness (high sat­u­ra­tion AND BRIGHTNESS) have high chroma. RGB colours that emit max­i­mum sat­u­ra­tion red light range from very low chroma (nearly black) through mod­er­ate chroma (dark ruby reds) to very high chroma (bright red or R 255). The impor­tance of this con­cept of sat­u­ra­tion for painters comes from the fact that when a coloured sur­face turns from shade into light, the colours of the light reflected from it tend to fol­low a uni­form sat­u­ra­tion series such as this.

And darn it, he’s right. Thanks, David. As this Wikipedia entry on col­or­ful­ness puts it:

col­or­ful­ness is the per­ceived dif­fer­ence between the color of some stim­u­lus and gray, chroma is the col­or­ful­ness of a stim­u­lus rel­a­tive to the bright­ness of a stim­u­lus that appears white under sim­i­lar view­ing con­di­tions, and sat­u­ra­tion is the col­or­ful­ness of a stim­u­lus rel­a­tive to its own brightness.

I, with my obvi­ously very small brain, still find it most use­ful to think about color using the char­ac­ter­is­tics of value, hue, and chroma. But sat­u­ra­tion does not mean what I said it does. I apol­o­gize for any confusion.

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10 Responses

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  1. Katarzyna says

    Hi David, I’m glad that you are back. To be hon­est I’ve started to worry about you. My com­puter sends me stub­born mes­sages that I can­not edit and send noth­ing to your site because of an error. I’m con­fused and not sure what is the prob­lem. Greetings.

  2. David Briggs says

    Sat­u­ra­tion in HSB refers to the rel­a­tive PURITY of colour of LIGHT, which in real­ity can vary from zero to its max­i­mum for light of any bright­ness. It isn’t really just some bad way of describ­ing chroma (the STRENGTH of the local colour of a SURFACE), it’s a dis­tinctly dif­fer­ent (and use­ful) con­cept. I’ve tried to con­cisely sum­ma­rize the dis­tinc­tions here:

    http://​www​.hue​val​uechroma​.com/​012​.​php

  3. David says

    Katarzyna,

    Replied in email.

  4. David says

    David,

    I don’t think sat­u­ra­tion in HSB is bad. I do think that, for the pur­pose of an artist mix­ing paint, the Mun­sell model, in which the scale from min­i­mum to max­i­mum chroma varies depend­ing on hue and value, is much more use­ful. In HSB, I can set chroma to 100%. If I then set the value slider to zero (black), the chroma is still at 100%. But there is no chroma there; the 100% is an arti­fact of the HSB model, in which 100% reflects max­i­mum chroma at what­ever the cur­rent value is.

    In Mun­sell, at a value of zero, the only pos­si­ble chroma is zero. That makes a heck of a lot more sense to me. It also bet­ter fits a sub­trac­tive color model, which is what we’re deal­ing with when mix­ing paint. As hue and value change, the range of pos­si­ble real-world chroma changes. HSB is per­fectly appro­pri­ate for com­puter soft­ware and other tech­ni­cal pur­poses. The con­sid­er­a­tions involved in design­ing com­puter inter­faces and cal­i­brat­ing mon­i­tors have noth­ing to do with paint­ing pic­tures, how­ever. So a dif­fer­ent model, more attuned to the messy real­i­ties of actual human color vision, is bet­ter for that purpose.

  5. David Briggs says

    To clar­ify, David, my objec­tion is that you seem to be judg­ing sat­u­ra­tion as if it was meant to be a mea­sure of colour inten­sity. It isn’t, it’s a mea­sure of colour purity. The term for inten­sity of colour of light is “col­or­ful­ness”, the prod­uct of the sat­u­ra­tion of a light stim­u­lus and its brightness.

    Many colours reflect light of high sat­u­ra­tion, but only those that reflect light of high col­or­ful­ness (high sat­u­ra­tion AND BRIGHTNESS) have high chroma. RGB colours that emit max­i­mum sat­u­ra­tion red light range from very low chroma (nearly black) through mod­er­ate chroma (dark ruby reds) to very high chroma (bright red or R 255). The impor­tance of this con­cept of sat­u­ra­tion for painters comes from the fact that when a coloured sur­face turns from shade into light, the colours of the light reflected from it tend to fol­low a uni­form sat­u­ra­tion series such as this.

  6. David says

    Thanks for the cor­rec­tion, David. I’ve updated this post.

  7. Roger says

    I agree with the author in that chroma has been more use­ful to me for mix­ing paint.

    I used to think you could buy your pri­mary col­ors; red, blue, yel­low, white, and black, and you could mix any color you wanted.

    But it wasn’t until I came across a set of paints that actu­ally listed the CHROMA of the color on the tube that I real­ized that the rea­son I couldn’t get really vivid col­ors was because you couldn’t mix a yel­low with a chroma of 12 with a blue with a chroma of 8 to get a green with a chroma of 14.

    Whereas accord­ing to sat­u­ra­tion you could mix white into it and you’re not decreas­ing the sat­u­ra­tion but you are decreas­ing the chroma.

    Cor­rect me if I’m wrong.

    • David says

      Roger,

      From the stand­point of a prac­tic­ing painter, the dif­fer­ence between sat­u­ra­tion (color purity) and chroma (color inten­sity) is fairly academic.

      You’re cer­tainly right that mix­ing paints almost always results in a color that is lower in chroma. For that rea­son, a three color palette has a lim­ited gamut of avail­able chroma.

  8. cara says

    clear as mud.

  9. krishna kumar says

    May l i know the dif­fer­ence between Bright­ness con­trast sat­u­ra­tion and sharp­ness also give the idea, how to do basic test­ing for same.



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