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Changing Luminosity for a specific Color Channel

Spicyjello
Hello,

Trying to change the luminosity for a specific color channel and not getting the expected results.

If I select an image, say a landscape with a blue sky and I want to darken the Blue channel. Using either Levels or Curves and select Blue and make an adjust to clip the shadows on levels, dragging the lower left most point to the right or simply darken overall in curves does not darken the Blue color channel it is shifting the tone to yellow. However, making the same adjustment selecting RGB will darken the overall image as expected. This just doesn't seem to work on a specific channel.

How can I simply darken the Red, Green or Blue channels? Selecting in the color editor does not produce the results as I want to darken ALL of the blue channel not just a range.

Thanks for the advice.

Troy
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Comments

6 comments

Date Votes
  • Ian Wilson
    Moderator
    Top Commenter
    If you reduce the brightness of the blue channel, that means that it is less bright in comparison to the other channels. You are in effect doing the same as increasing the brightness of the red and green channels (relative to blue). So you might expect it to become more yellow.

    You actually probably can do what you want (which as I understand it is to make all the blues darker) in the colour editor because you are not really limited to only a small range of the blue part of the spectrum. In the Basic tab of the colour editor you can select the blue slice of the pie but then drag its edges round the circle both ways to widen the range of colours you want to affect. Or in the Advanced tab of the tool you can click on a blue colour in your image and then adjust the width of the slice in the pie that this creates in a similar way (and use the Smoothness slider to control how sharply the effect is cut off at the edges of the slice). Also in the Advanced tab, of you don't get enough darkening of your colour by moving the brightness slider all the way to the left, you can click in the same place in the image again, and get a second adjustment of the same colour (they are cumulative).

    If you find that parts of the image you didn't want to be affected are being, then you can use the Advanced tab of the colour editor as a local adjustment.

    Hope that helps.

    Ian
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  • cdc
    Do you want to change the luminosity to the blue channel, or change the luminosity of the color blue in your picture?

    What other programs are you using that give you the results you're after, and how is that being achieved?
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  • Spicyjello
    Thanks for the advice!

    Ian - Good info. I didn't know the "lightness" was cumulative. That was a big help.

    CDC - I am currently using LR. When in LR HSL tab, selecting the Blue color channel and luminosity. Dragging to the left will darken that blue channel. This is the result I was looking for. In C1 is responds completely different. Im just having a hard time wrapping my head around what it is that C1 is doing with the channel.

    My goal is to select a specific color channel and darken. Not always a color needs to be selected but the entire channel. As Ian explained I can do that by selecting in the Color Editor but the results are a little different.

    I will continue to test.

    Thanks again!

    Troy
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  • cdc
    I am a bit confused by your terminology. I think you are trying to adjust the color blue and not the blue channel. In lightroom the using the HSL tool tab would only effect the color blue, not the blue channel itself. The only ways to adjust the blue channel in lightroom is to use the curve tool set to the blue channel, or the camera calibration tools. Any adjustments there will change all of the colors in the image, as Ian mentioned.

    But yes, Capture One's version of HSL is the color editor tool. They essentially both do the same thing only with Capture One you can adjust the range of colors you are selecting as opposed to HSL which is predetermined. I think with some experimentation you will find the color editor is actually more powerful than lightrooms HSL because of this, you can dial in a broader or smaller color selection. Ian's advice is good advice, use the advanced tool and make your color selection then make adjustments with the selection in the color wheel to get an idea of how the tool works.
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  • Spicyjello
    Thanks for the info. I will certainly spend some time testing the Color Editor. I see how its very powerful.

    Thanks again!

    Troy
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  • SFA
    In addition for the foregoing replies it may be worth just mentioning here that the "Skin Tone" editing feature us a variation on the colour editing theme that may be relevant sometimes to things like sky and water areas.

    Although the concept of the tool is intended for smoothing and matching skin tones for a more consistent beauty result the same thing can be useful for any tonal gradient with water and sky areas being good targets and darkening and lightening possible.

    Also any tool that can be used in a local adjustment offers extended capabilities for specific selections of the image to which adjustment should be applied. This may offer far more control than might appear to be the case when fisrt investigated.

    HTH.


    Grant
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