Color/Luminosity separation

Started 3 months ago | Discussions thread
JohnWheeler Contributing Member • Posts: 629
Re: Color/Luminosity separation

Currantos wrote:


I've read early a general statement about more advanced workflow where one separates the color and luminosity on different layers and then works on each separately.

I've looked up a few tutorials and experimented, kind of getting inconsistent results since there are different 'luminosities'.

Anyone has helpful simple way to do it?

In that tutorial they separated luminosity and color AND did frequency separation, so there was no 'color contamination' and color stayed consistent throughout.

At that time when I read it I did not have enough PS knowledge to fully understand the details and commit it to memory, only got the vague idea. Now that I am a little further ahead in PS I'd like to recreate that workflow and I see advantages to working separately on luminosity/color.

Thanks everyone

Hi Curantos

Here is a way to stay in RGB mode and separate out Color from Luminosity so you can work on the Luminosity separately.  Some have referred to this technique in the other posts yet I will give you the step by step.

Before some notes:

Yes there are a number of color models that separate out Luminosity, Brightness, etc out from Color, Hue, Sat.  Each model will also end up with a slightly different result (including if you went to Lab).  Even in Photoshop they refer to Saturation in different places and they are not the same.  So yes it can be confusing.

The model I am showing you below is based on the Blend mode definitions of Luminosity and Color.   Color in this case has two components being Hue, and Saturation.

Luminosity in this model is =  .3*R + .59 * G + >11 *B values for each pixel.

I separate out the Luminosity to the Lower Layer.  The Upper Layer is actually just the original image with the Blend mode set to Color.  That forces the resulting image to use the Luminosity from the Lower Level and Just the Color from the upper Layer.

So you can modify the Lower Layer at will for luminosity effects and either leave the upper Layer alone (to best preserve the original Color) or adjust to the desired Color.

Here is the caveat.   It is impossible to have all combinations of Luminosity, Hue, and Saturation totally preserved.  e.g. if you make the luminosity all white and then combine it with any color, this color mode/model will remain totally white.

Here is how Luminosity and Color is combined.   First the Luminosity is preserved and also the Hue is preserved.  If the luminosity ends up being too high, then the saturation is sacrificed a bit (again under this color models definition of saturation).  Something just had to give.  Yet, the end result will be a lot closer to the original color than many other approaches.

Here are the images with the step by steps

First duplicate your image, set the upper image to Blend of Color and then turn off visibility

Nest step is to add a pure white Layer above the original image layer (the lower layer) and also set the blend mode to color.  Since white has no color the result is just the Luminosity as shown below:

Now just merge down so the bottom Layer is the Luminosity of the original image:

All I did with this last image is turn the visibility back on of the upper "Color" Layer and what you see is the original image even though it is the combination of the images Luminosity Layer below and just Color of the upper Layer combined together:

So now you an operate on the Luminsity alone by itself by adjusting the Lower Layer any way you want and still maintain the Color of the second Layer.  You can adjust the Color of the second Layer independently if desired.

Hope this helps showing the step by step.  This is not the only approach yet one I have used often.

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John Wheeler
Never give up. Never surrender. Galaxy Quest

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