martinimages
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A brief look at channels
Hers a brief look for those that are starting in BW conversion.
First heres the original col version
Using channel mixer the examples below show how different channels effect tonal and grey responce, the first image is using the red at 100% G&B to zero
You can see that the red channel although good for the sky it has produced a flat caravan image, the whitish curtains have turned mid grey the mans body tones are to white
Heres the next image set in C/M to 100% green, R&B at zero
It can now be seen the tonal range and contrast is much better with a seperation in tones
Now heres the last image set in C/M at 100% Blue R&G set to zero
With the blue channel its again gone a touch flat and the greens and shadows are a lot darker than needed in this picture, plus skin tones are to dark
Heres the finished image using all the channels selectivly using layer masks and painting back where needed, [i added a warm tone to this ]
As you can see doing a selective use of channels does various improvments , increases contrast without blowing highlights, retreaves shadow detail with no blocking out and gives a more natural tonal look with smooth gradation of tones etc, once this is achieved other careful adjusments can be done,EG USM to localy increase sky detail, levels to lighten or darken certain areas to taste etc etc, unfortuantly re sizing has taken some of what i have just said out of the image so not all tones are visiable but trust me there all there  , hope this helps some of you its all simple sfuff no high tech once you master using layer masks and painting back your there, its a way that we used to work in the wet dark room using multigrade filters to alter the tonal range to different parts of the projected image, this is much easier and not half as smely and messy 
Martin
Last edited by martinimages, 18/Jun/06, 1:37 pm
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18/Jun/06, 1:32 pm
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Carbon Based
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Re: A brief look at channels
I've read on the web that the combination of the RGB channels should add up to 100. But no one has explained why. Why not 90 or 110? Any explination on this.
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25/Sep/06, 1:08 am
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crimbo
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Re: A brief look at channels
quote:
Carbon Based wrote:
I've read on the web that the combination of the RGB channels should add up to 100. But no one has explained why. Why not 90 or 110? Any explination on this.
Like many other myths...8/16 bit,sRGB/Adobe RGB,conversion to and from LAB...they are reasonable hypotheses which have been taken as fact before being proven.
Your channels can add up to anything you like...experiment and you will find out how different images can keep or lose information
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25/Sep/06, 6:21 am
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martinimages
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Re: A brief look at channels
Ditto as chris
Martin
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25/Sep/06, 5:35 pm
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