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Contrast vs. saturation

Discussion in 'Image Processing' started by relic, Mar 15, 2019 at 5:35 PM.

  1. relic

    relic Mu-43 Top Veteran Subscribing Member

    800
    Oct 21, 2010
    North Carolina, USA
    When I increase contrast, saturation appears to also increase, at least perceptually. Other than desaturating colors ("to taste"), is there a way to increase contrast without making the colors look more saturated? Or am I simply confusing the two? Many thanks.
     
  2. Frogwatch

    Frogwatch Mu-43 Regular Subscribing Member

    98
    Dec 13, 2016
    Perth, Australia
    Matthew
    Yes this is a thing. There are many ways to add contrast to an image, and they may muff up the saturation of the colours in the process.

    The misconception of RGB curves / ColorPerfect - The misconception of common curve adjustments
    (there are many other explanations out there, and I'm not even going to pretend I read this whole article)

    Capture One offers luma curves to adjust contrast while minimising impact on saturation.
    Refine Your Images Contrast With This Simple Capture One Pro Tool

    I'm not familiar enough with Adobe products for their equivalent - a quick google revealed nothing easily accessible but there may be a way. Send help Adobe users.
    :th_salute:
     
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  3. rloewy

    rloewy Mu-43 Hall of Famer Subscribing Member

    May 5, 2014
    Ron
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  4. relic

    relic Mu-43 Top Veteran Subscribing Member

    800
    Oct 21, 2010
    North Carolina, USA
    Many thanks to @Frogwatch@Frogwatch and to @rloewy@rloewy for their quick, very helpful replies. After reading them (but I've not yet read the links-- thanks for providing those which I'll read later), something came back to me: when I first started to edit digital photos, I started with gimp, and I still remember a few fancy things it did, including decomposing the image into LAB channels, and I remember that the L channel contained the light level information but no color information (I just confirmed this using Wikipedia), so then if I increase the contrast of the L channel and then recombine the channels, I might (I am hoping) get an increase in contrast without changing the saturation. I have gimp, but I've not used it for years. I'll try and see if this would work. Thanks again, and I'll report back whether I succeeded or not.
     
  5. relic

    relic Mu-43 Top Veteran Subscribing Member

    800
    Oct 21, 2010
    North Carolina, USA
    I tried cecomposing the image into LAB color space, increasing the contrast in the L channel, and then recomposing the image, and it seems to work as expected (at least to my eyes): contrast increased without a concomitant increase in color saturations. The example below is extreme: I first edited the raw file in DXO, and decreased the contrast by pulling the contrast slider all the way to the left. Then I edited the file in gimp. First image: I increased the contrast (using curves) and exported it as a jpeg. The 2nd image I simply exported it without any contrast changes. The third image I decomposed it into LAB channels, increased the contrast of the L channel (same amount of contrast increase as the first image), then combined (use compose, not recompose) the channels. It just occurred to me that I think it would be nice if software did this automatically and transparently when contrast is changed, given the sophistication of current editing software.

    1. Increased contrast in RGB image.
    increased_contrastM.jpg
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    2. Original image.
    originalM.jpg
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    3. Decomposed into LAB, increased contrast in L channel, then combined the channels.
    lab-composeM.jpg
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    Many thanks again for the help (which triggered my memory...) I learned something new about a problem that has been bugging me for a long time.
    I wonder if there are other things that modifying the L channel would be useful for: comments will be appreciated.

    Again, many thanks to @Frogwatch@Frogwatch and @rloewy@rloewy. I looked at the links you provided, and all three are very relevant, but to my aging brain, are complex enough to require careful studying to hope to understand them. But two of them talk about LAB color space, so that makes me more confident that what I tried above may be correct. I'll try to read them later when my mind is a bit clearer.
     
    Last edited: Mar 15, 2019 at 8:48 PM
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  6. rloewy

    rloewy Mu-43 Hall of Famer Subscribing Member

    May 5, 2014
    Ron
    That sounds very reasonable as this color space separates the "light" from the "color/hue" portion (a bit like HSL) - so working only on that channel should not change any of the saturation / color.

    I do not use GIMP so I am not certain - but your solution makes a lot of sense given the specifics of using this color model and software that can work on a specific channel
     
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  7. relic

    relic Mu-43 Top Veteran Subscribing Member

    800
    Oct 21, 2010
    North Carolina, USA
    Many thanks. I need to study the links to understand better what I'm doing. But even knowing only that the L channel only has the "light" information is very useful. When I have time I'll try to play around with the "a" and "b" channels to see how they affect the image, just out of curiosity. Thanks again.
     
  8. pellicle

    pellicle Mu-43 Hall of Famer Subscribing Member

    Feb 10, 2010
    Killarney, OzTrailEYa
    pellicle
    myself I solve this by loading the RAW file and then adjusting it to taste. Happily I'm not working with advertising where product managers will get involved and say that the packet of cereal is over saturated or the wrong hue.

    Its an interesting read and I find that its nicely solved in some applications with a saturation slider exactly below the strength slider ...

    Of course when I was back working with scanning colour negative anyone was happy just to get decent colours out of that ;-)
    6x12-008.jpg
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    Last edited: Mar 16, 2019 at 7:43 AM
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  9. Frogwatch

    Frogwatch Mu-43 Regular Subscribing Member

    98
    Dec 13, 2016
    Perth, Australia
    Matthew
    There is a luminosity add-in for Gimp that will split up the image into different masks (light --> dark) and then you can work on each mask individually. This probably isn't as technically correct as working with the LAB colour space, but it may be a little quicker and get similar results?

    Add-in
    https://www.daviesmediadesign.com/shortcut-script-developed-kevin-thornton-luminosity-masks-gimp/

    Tutorail of creator using plugin


    To be honest every time I've attempted to learn Gimp I've been confused. o_O 
    Good luck to you sir.
     
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  10. relic

    relic Mu-43 Top Veteran Subscribing Member

    800
    Oct 21, 2010
    North Carolina, USA
    Thank you very much for the suggestions. Yes, I have found that gimp is rather bewildering. Although I had used a much earlier version many years ago, the version I have now is so much more complex. I am guessing that once one gets the hang of how it operates, it won't be as intimidating, but so far I've only figured out how to decompose the image into LAB then recompose it, and have managed to crash the program when I tried to export the result (so I had to start over :)  ). Yet for cases where it is important to keep the saturation but incraase the contrast significantly, I think it would be worth using it just for that (it would add a few minutes, but I do this for fun, so that wouldn't be a problem). Many thanks for the links-- apparently there are quite a few helpful videos but I am still trying to learn/figure out DXO Photolab, so gimp has to wait...
     
    Last edited: Mar 16, 2019 at 8:38 PM
  11. Giiba

    Giiba Something to someone somewhere Subscribing Member

    Aug 19, 2016
    New Westminster, BC
    Last edited: Mar 17, 2019 at 10:53 AM
  12. TheMenWhoDrawSheeps

    TheMenWhoDrawSheeps Mu-43 Top Veteran

    502
    Jun 15, 2016
    if you´re using photoshopthere are few solutions.
    basic
    layer luminocity
    - set adjustment curve/contrast/lvlto luminocity, doesn´t affect color that much.

    advanced
    flat curve profile
    make hue layer desaturate, set it to soft light.
    create adjustment curve linked to hue, and set start and end point to middle grey (127). you can pick points you want to adjust on curvewith pipette. gives you more control over dark/bright areas, and is far more logically to understand.
     
  13. ToxicTabasco

    ToxicTabasco Mu-43 Top Veteran

    994
    Jul 2, 2018
    South West USA
    In most editing software, adding contrast lightens highlights and darkens shadows. Thus, it brightens bright colors and darkens the darker colors of the scene. As a result it look more saturated because the dynamics of the color has changed. Thus, if you ad contrast, you can reduce saturation.

    Knowing this can help capture more color in a scene. One thing I like to do is underexpose sunsets and get more color detail to work with in editing. This helps protect the highlights, but gives color and detail to the highlights.
     
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