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how to separate colour and luminance from RGB

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  #1  
Old 06-08-2011, 07:30 AM
ISO ISO is offline
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how to separate colour and luminance from RGB

Hello friends

I want help (detailled tutorial) for separating colour and luminance from RGB.

Thanks in advance.

Regards

Mukund
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  #2  
Old 06-08-2011, 08:08 AM
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Der_W Der_W is offline
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Re: how to separate colour and luminance from RGB

The easiest way would be to simply use the "Luminosity" and "Color" blending modes, so your adjustments will just affect the components you told it to.

If you want to extract the luminosity, one easy way would be to add a new layer in "Color" mode and fill it with 50% gray.
If you want to extract the color, add a new layer in "Luminosity" mode and fill it with 50% gray.

Other methods using Apply Image or the Channel Mixer would work as well, but are probably overkill.
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Old 06-08-2011, 08:16 AM
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John Wheeler John Wheeler is offline
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Re: how to separate colour and luminance from RGB

Hi Mukund
ADDED EDIT: Jonas beat me to it while I was typing
Kind of depends on your definition of luminance and colour. Photoshop is not consistent in how it is used throughout their software offerings including not totally consistent within Photoshop itself.

Here is a link to a overall reference document that covers many math details of what Adobe does from a math standpoint in much of their software. Blends start on page 320 and near page 326 is where they get into the details of their Luminosity, Color, Hue,Sat blend modes which reveals their definitions through the equations. Note that their definition of Saturation does not match how the numbers for saturation is used in their Color Pickers:

http://wwwimages.adobe.com/www.adobe...32000_2008.pdf

That may be more than what you want. So it may help for you to be more specific on what you are trying to achieve to get more specific answers.

Here are some basic techniques to extract Luminance and Hue

1) To extract Luminance.
- Lower layer is image
- Next higher layer is a neutral tone layer (white, black, or any shade of gray). Set the Blend mode of this neutral tone layer to "Color". The resulting image is the Luminance where all RGB values are equal where the Luminance is defined by L= .3R + .59G + .11 B

2) To extract Hue
- Lower Layer is solid 50% gray
- Next Layer up is your image. Set the Blend mode of your image layer to Color. The resulting image will be an image where the Luminosity is 50% for all pixels yet all the pixels will have the exact Hue of you original Image. The blend will try and keep the Saturation yet will give precedence to the Luminosity first. Note: There are other techniques depending on what you want to do.

I think I will stop there because what you need is really dependent on what you want to do. Provide more details on what you are trying to do and forum members could provide more specific answers. Hope this gives you a start.
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Old 06-09-2011, 02:23 AM
ISO ISO is offline
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Re: how to separate colour and luminance from RGB

Thanks Jonas and John. Its kind of you to give reply in detail.

Actually what I want is this

http://img135.imageshack.us/i/curveslayer.jpg/

Could you pl. share detail tutorila how to do this?

Thanks again.

Regards,

Mukund

Last edited by ISO; 06-09-2011 at 02:37 AM.
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  #5  
Old 06-09-2011, 05:20 AM
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Chain Chain is offline
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Re: how to separate colour and luminance from RGB

Quote:
Originally Posted by ISO View Post
What Jonas said would let you do this (The Lum/Color layers, not the RGB layers).

Here are more detailed steps:
1. Make a copy of the original image layer, set it to "Color" blend mode.
2. Create a layer with 50% gray below it.
3. Merge the two layers. You now have a layer with the color information.
--
4. Make a copy of the original image layer, set it to "Luminosity" blend mode.
5. Create a layer with (any shade of) gray below it.
6. Merge the two layers. You now have a layer with the luminosity.

If you have the Color layer on top, set the blending of it to "Color".
If you have the Luminosity layer on top, set the blending mode of it to "Luminosity"
(The layer with the original image can safely be hidden/removed).

If you do this regularly, you should record the steps as an action.

Note: Usually there is no need to create a separate layers for Lum. and Color. It's usually easier and more efficient to do simply add Lum./Color blending mode to whatever corrections you do to the image (as layers).
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  #6  
Old 06-09-2011, 06:05 AM
edgework edgework is offline
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Re: how to separate colour and luminance from RGB

Quote:
Originally Posted by ISO View Post
Thanks Jonas and John. Its kind of you to give reply in detail.

Actually what I want is this

http://img135.imageshack.us/i/curveslayer.jpg/

Could you pl. share detail tutorila how to do this?

Thanks again.

Regards,

Mukund
What is it that we are looking at? Explain what the starting point is, what the desired end result is. Several processes described here are what would normally be thought of as accomplishing what you asked about. The image you linked to would seem to have nothing to do with any of those procedures.
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Old 06-09-2011, 07:28 AM
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Chain Chain is offline
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Re: how to separate colour and luminance from RGB

Quote:
Originally Posted by edgework View Post
What is it that we are looking at? Explain what the starting point is, what the desired end result is. Several processes described here are what would normally be thought of as accomplishing what you asked about. The image you linked to would seem to have nothing to do with any of those procedures.
To me the picture was relevant, although the RGB layers at the bottom might make it confusing as they do not contribute to anything.
From what I can tell we are looking at an image where at the bottom we have the RGB channels converted to separate layers (screen blend mode). Above that we have the same image separated as Luminosity+Color instead (overriding the below layers).

Edit: Attached is a much better example showing what we are doing.
Attached Images
File Type: png lum&color-layers.png (44.0 KB, 126 views)
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  #8  
Old 06-09-2011, 10:21 AM
ISO ISO is offline
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Re: how to separate colour and luminance from RGB

Thanks again friends. Attached image is what lobster droplet from free gamma is doing.

It splits rgb image in to separate colour component and luminocity. This divide gives very powerful editing options like dodge and burn and selective colour adjustments.

Pl. Share detailed steps how to do this.
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  #9  
Old 06-09-2011, 10:37 AM
julianmarsalis julianmarsalis is offline
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Re: how to separate colour and luminance from RGB

so cool anyone have an action lmao yes i am that lazy >.>.....
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  #10  
Old 06-09-2011, 12:41 PM
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lurch lurch is offline
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Re: how to separate colour and luminance from RGB

If you convert the image to Lab, it's done for you. And you can make a smart object from an RGB image, then convert the SO to Lab without affecting the RGBness of the original image. Or am I missing the point?
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