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how to separate colour and luminance from RGB

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  #11  
Old 06-09-2011, 12:54 PM
ISO ISO is offline
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Re: how to separate colour and luminance from RGB

Edit- friends because of your valuable information im successful in achieving what i want. Its working.

Thanks again.
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  #12  
Old 06-09-2011, 12:55 PM
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Chain Chain is offline
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Re: how to separate colour and luminance from RGB

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Originally Posted by ISO View Post
Pl. Share detailed steps how to do this.
I already did back in this post:
http://www.retouchpro.com/forums/pho...tml#post292588
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  #13  
Old 06-09-2011, 01:20 PM
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Chain Chain is offline
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Arrow Re: how to separate colour and luminance from RGB

Quote:
Originally Posted by lurch View Post
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?
With LAB it means you have to will have to convert color spaces. Beware that in 8-bit there is always some loss from this, and unless you go via Convert to Profile it will add more noise/dithering in the process. This is not a visible problem if working in 16-bit.
In the conversion you will loose all layers, and you have much more limited tools in LAB.
You can get just as good results using Luminosity and Color blending modes.

You could stamp a copy of the image, convert it to a smart object, open the smart object, work directly on one of the channels instead of working in layers, save and then jump back out of the smart object to see the result with the rest of the layers... I find this cumbersome compared to simply doing the adjustment on a new layer and change the blending mode.

I strongly believe that there is never a need to go through all this to work on color and luminosity separately. You gain nothing (at worst you loose flexibility and add extra noise). It is quick and simple in RGB.

----

I have attached an action for you that does the Color/Luminosity separation as layers. I included some frequency separation actions and sharpening actions as well just to make the set more useful... :=)

The actions should run well even on layered documents and foreign language versions of Photoshop (report back if they don't).
Attached Files
File Type: zip Separations.zip (1.9 KB, 66 views)
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  #14  
Old 06-09-2011, 01:29 PM
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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
Jonas, Chain, and I are all saying the same thing and it is exactly what they are also doing in Lobster droplet. Here is a specific layers stack showing how this is achieved with to make it more explicit using the same colors in your example:

Screen shot 2011-06-09 at 12.14.45 PM.png

Lets look at top three layers first

- Original File
- On top of that is neutral tone layer (black, white, any shade of gray) with Blend set to Color
- Resulting image is the luminosity which is stamped to the top layer to make it visible in the stack.

Lets Look at the bottom three layers
- Original File
- On top of that is a 50% gray layer with Blend set to Luminosity
- The resulting image are the colors of the image at Luminosity 50%. That is stamped to the next layer so you can see it in the Layer Stack and I named it "Color"

Now to separate out the 3 color channels (there are many ways to do this)
- Above the "Color" layer I put a Curves Adj Layer
- Turn down the Green and Blue Curves to Zero (flat at bottom). This yields the Red Channel. I stamped it to make it visible in Layer Stack
- To get Green channel repeat with Curves Adj turning off Red and Blue channel. Then stamp it
- To get Blue channel repeat with Curves Adj turning off Red and Blue channel. Then stamp it

That is all there is to it (and no I did not make an action)

EDIT - Lots of other inputs since I started typing - wow
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  #15  
Old 06-09-2011, 02:16 PM
julianmarsalis julianmarsalis is offline
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Re: how to separate colour and luminance from RGB

Quote:
Originally Posted by Chain View Post
With LAB it means you have to will have to convert color spaces. Beware that in 8-bit there is always some loss from this, and unless you go via Convert to Profile it will add more noise/dithering in the process. This is not a visible problem if working in 16-bit.
In the conversion you will loose all layers, and you have much more limited tools in LAB.
You can get just as good results using Luminosity and Color blending modes.

You could stamp a copy of the image, convert it to a smart object, open the smart object, work directly on one of the channels instead of working in layers, save and then jump back out of the smart object to see the result with the rest of the layers... I find this cumbersome compared to simply doing the adjustment on a new layer and change the blending mode.

I strongly believe that there is never a need to go through all this to work on color and luminosity separately. You gain nothing (at worst you loose flexibility and add extra noise). It is quick and simple in RGB.

----

I have attached an action for you that does the Color/Luminosity separation as layers. I included some frequency separation actions and sharpening actions as well just to make the set more useful... :=)

The actions should run well even on layered documents and foreign language versions of Photoshop (report back if they don't).
Dude you rock Christmas came early this year thanks again!!!!
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  #16  
Old 06-09-2011, 02:18 PM
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lurch lurch is offline
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Re: how to separate colour and luminance from RGB

@chain - I think you will find that there is essentially no loss in converting to Lab. But what you find convenient in your workflow is whatever you find convenient. Have to admit that I rarely use Lab any more, because when I have to separate luminosity and color (especially in restoration work), it's with luminosity and color layers.
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  #17  
Old 06-09-2011, 02:18 PM
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Tony W Tony W is offline
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Re: how to separate colour and luminance from RGB

Quote:
Originally Posted by Chain View Post
With LAB it means you have to will have to convert color spaces. Beware that in 8-bit there is always some loss from this, and unless you go via Convert to Profile it will add more noise/dithering in the process.
While I can see that some conversions between colour spaces can be harmful I have not really experienced issues (yet!) with converting to LAB either 8 bit or 16 bit and converting back again to RGB. Or at least I have not noticed any that had a detrimental effect on the final image!!

What kind of losses can you expect and how much will be observable in a real world image? Do you have any examples (or links) that illustrate the issues?
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  #18  
Old 06-09-2011, 02:46 PM
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John Wheeler John Wheeler is offline
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Re: how to separate colour and luminance from RGB

Hi Tony
I have seen issues in 8 bit going back and forth to Lab and why I suggest staying in 16 bit for that operation. It can be demonstrated very easily.

Here is a 256px x 256px image with all 256 gray levels represented one per pixel column (100% view):

Screen shot 2011-06-09 at 1.37.30 PM.png

If you have in Edit > Color Settings the dither turned off, if you take this to Lab and back and do the difference, and just amplify the differences (i.e. anything other than a perfect match is pegged to 255) here is the image you see:

Screen shot 2011-06-09 at 1.37.49 PM.png

If you do the same experiment and and have the Color Setting mode so the dither is "on", then here is why you get:

Screen shot 2011-06-09 at 1.38.11 PM.png

The differences are only 1 bit differences however it does make a difference. With dither turned off, in slowly changing colors such as skies, the changes can jump two bits instead of 1 bit and this causes increased noticeable banding (let me know if you want me to post an image)

With dither turned on, you don't notice the banding yet you end up with noticeable 1 bit mottling (again I can post an image if desired).

So I agree with chain, conversion between some color spaces will create artifacts in your image that can be noticeable.
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  #19  
Old 06-09-2011, 02:47 PM
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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 John Wheeler View Post
- Turn down the Green and Blue Curves to Zero (flat at bottom). This yields the Red Channel. I stamped it to make it visible in Layer Stack
Ah, that's a nice way to turn the layers into channels. I didn't think of that.
Only time I've really needed to turn channels into layers was when I was making some 2-strip Technicolor actions. I will keep it in mind next time.

Last edited by Chain; 06-09-2011 at 02:51 PM. Reason: Minor clarification.
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  #20  
Old 06-09-2011, 02:50 PM
John Wheeler's Avatar
John Wheeler John Wheeler is offline
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Re: how to separate colour and luminance from RGB

Hi Chain
Another easy way to get the Channels into Layers is with the Channel Mixer
Adjustment Layer. You just leave the channels you don't want with all mixer values set to zero. Works like a charm.
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