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HELP using channel mixer please !

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  #11  
Old 09-15-2006, 05:25 PM
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mistermonday mistermonday is offline
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Alain, two questions for you:
1. Was the layer opacity set to 100% prior to your application of the channel mixer? If it was not, then your results will be different.
2. Did you compare the files (or layers) prior to saving them as jpgs? If not, then do so or save the files as PSD.

I tried a number of other tests, yet I still get the same results - everything is identical. Included in the tests were checking of the Monochrome button and verifying that the resultant gray scale image had a 3 channels which were identical to the original Red channel - and they were.

So if it still does not work for you, please post a detailed description of all of the steps that you are taking in the process.
Regards, Murray
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  #12  
Old 09-15-2006, 06:33 PM
Pam Pam is offline
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I believe what Alain is trying to say is that the red channel for any given image is slightly different depending on the manner in which it's created. If it's copied from the channel's palette, it's brighter than if it's created using the channel mixer. As a test, try this:

1 - Open an image.
2 - Open a channel mixer adjustment layer and use these settings:
R - 100, G - 0, B - 0, check monochrome.
3 - Open a new layer and hit Ctrl+Alt+Shift+E to merge all visible layers onto the new layer.
4 - Now turn off all layers. You should now have only the original background image visible.
5 - Open the channels palette. Click on the red channel. Hit Ctrl+A (select all), then Ctrl+C (copy). Now click on the RGB composite channel and return to the layers palette.
6 - Open a new layer and hit Ctrl+V to paste the red channel (copied from the channels palette) into the new layer.
7 - Click on the layer you created in step 3 (the red channel created from the channel mixer). Compare these two and you will find that the channel palette's red channel is different from the channel mixed red channel.

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  #13  
Old 09-15-2006, 08:20 PM
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mistermonday mistermonday is offline
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Pam, thanks, now I understand what Alain is doing. Actually there is a much simpler way to demonstrate the effect. You do not need to do a channel mixer, you can simply create a dummy image in which you fill the any channel with a value (for example 20), then copy it and paste it into a new layer and the value it will read is 29 (for sRGB).
The issue is that Channels do not equal layers. Channels are always fixed mathematical values of 0 to 255 in the case of RGB and 0 to 100 in the case of LAB. When you copy the contents of an alpha channel and turn it into a layer, it needs to conform to the Color Space that you are working in.

You can see this if you repeat the example above but convert the color profile (Edit>Convert to Profile) and change from sRGB to AdobeRGB. The 20 that was in the red channel becomes 41. When you copy it and paste it into a new layer, it will measure 60. If your image was a solid shade of blue (R=20, G=60, B=100) in sRGB mode, when you change it to Adobe RGB, the values will change but the color you see on your monitor is the exact same color blue.

That's partly why there are a whole set of commands for mathematically manuipulating channels and layers.

Regards, Murray
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  #14  
Old 09-15-2006, 08:45 PM
gmitchel gmitchel is offline
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I have a free action set that includes lots of Channel Mixer recipes. It also includes several other methods of B&W conversion. That way you can quickly and easily compare the results of different ways of converting to B&W.

http://www.thelightsrightstudio.com/...Conversion.htm

Cheers,

Mitch
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  #15  
Old 09-15-2006, 11:18 PM
Pam Pam is offline
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Quote:
Originally Posted by mistermonday
When you copy the contents of an alpha channel and turn it into a layer, it needs to conform to the Color Space that you are working in.
Ahhhhhhhhh!! I have been wondering about this phenomenon for a few years now.It seems that very few people notice it and fewer still have even ventured a guess at what is actually happening. Thank you for clarifying!


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  #16  
Old 09-17-2006, 06:51 AM
alain754 alain754 is offline
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Smile

Great !!!! Murray and Pam, that's exactly what's happening !!!! Thanks for thios explanation !!! The behaviour was not very intuitive .... I was thinking too basically, forgot the color space question !

Merci !
Alain
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  #17  
Old 09-17-2006, 06:54 AM
alain754 alain754 is offline
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Mitch thanks for the link, in fact, I downloaded them few month ago already ! Thanks for your site too !!!
Alain
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  #18  
Old 09-17-2006, 07:35 AM
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skydog skydog is offline
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Phil,

Thank you for linking the video tutorial. Do you know where one can find the "action" that is presented?
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  #19  
Old 09-17-2006, 10:01 AM
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mistermonday mistermonday is offline
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Go to www.atncentral.com then clik the Downloads button and scroll down about just past the half way point on thaat page.
Regards, Murray
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