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Photoshop Channel concepts: The Power of Ten

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  #51  
Old 05-25-2011, 12:14 PM
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Re: Photoshop Channel concepts: The Power of Ten

One of the really neat tricks Lee showed was how to desaturate shadows. In his video, he saves off a copy of the document, converts to CMYK, pulls curves on the Black channel and loads that into the master. Here’s where I’m somewhat confused. He creates a solid color layer with a 50% solid gray, loads the K channel into the mask and sets the blend for Color. That indeed desaturates the shadows nicely. But why the Color Fill layer? I tried this same technique and used the Vibrance/Saturation adjustment layer and loaded the K mask into that layer mask. I found this was a bit more useful here is I can control either the Vibrance or Saturation slider to fine tune the effect. With the 50% Color Fill, you don’t get the same degree of control. Yes you can alter the layer opacity, but I can do that too with the Saturation Adjustment layer. So the question for all you “power of 10” guru’s is why use Solid Color/Color Bend mode?

I also think playing around with different CMYK profiles or separation options may make this more powerful (altering GCR and blank gen). But for now, the default SWOP V2 does the job.
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  #52  
Old 05-25-2011, 01:39 PM
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Re: Photoshop Channel concepts: The Power of Ten

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Originally Posted by andrewrodney View Post
In his video, he saves off a copy of the document, converts to CMYK, pulls curves on the Black channel and loads that into the master.
FWIW, for someone like me who just hates the idea of leaving RGB, I tried building a black plate like image just using Lightroom. Made a virtual copy. Set curves for linear, adjusted the raw VC to look very much like a black plate. Saved the preset so in the future, one click and I’m done. Rendered the high bit data into Photoshop and loaded that into the Layer Mask. Worked like a charm. Histogram shows a much cleaner (no data loss) compared to using 8-bit per color CMYK Black channel.

I suspect that if one plays around, much of the grayscale channel stuff needed can be done from the raw data. What’s interesting is the techniques described thus far take an image in need or correction and build channels from this less than ideal data and its channels. But altering sliders in the raw converter to first improve the data, then using a VC and creating a grayscale rendition to then load in Photoshop seems to be quite workable. The VC takes up no more disk space. The new data used for mixing the channels is super pristine. What’s really interesting is using the Calibration sliders on a B&W image! You can do some interesting grayscale work to then load as a channel once in Photoshop. And it doesn’t matter what channel from the rendering you select (Master, R, G or B), they are all identical.

Last edited by andrewrodney; 05-25-2011 at 01:54 PM.
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  #53  
Old 05-25-2011, 01:50 PM
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Arrow Re: Photoshop Channel concepts: The Power of Ten

andrewrodney: The grey (any shade will do) layer with color blend mode is just one way to get a layer that desaturates stuff. As you say, a Vibrance adjustment layer gives you more flexibility, so I would recommend that instead (but keep the blend mode as color).

Going all the way to CMYK just to use the K-channel as a luminosity/brightness mask is slow, and it will not be more accurate than any of at least 4 other ways of doing it (that I can think of right now). I would go like this:
1. Ctrl/cmd-click the RGB channel. (load channel as selection)
2. Add Vibrance adjustmeny layer.
3. Invert mask (cmd/ctrl-i).
4. Set blending mode to color.
5. Increase or decrease saturation/vibrance to taste.
(5. Hit cmd/ctrl-m to do a curves adjustment on the layer if I need to more narrowly attack a brightness range. Or use "blend if". Or another mask.)

As you can see, step 1 completely bypasses making a copy of the document, going to CMYK, and copying the black channel into the master document. Easy and quick. The rest is just tweaking that you would do either way.

If you feel that the RGB "channel" is not a good enough representation of the brightness information in the image (it usually will be), you could add a layer that desaturates your image (black & white, gray solid color, hue/saturation, etc.) and set blending mode to "color" (or "saturation"). Then load the RGB channel.
This is perceptually more accurate as the color/saturation blend modes (and hue/luminosity) weights the RGB information based on how sensitive our eyes are to each color.
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  #54  
Old 05-25-2011, 02:03 PM
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Re: Photoshop Channel concepts: The Power of Ten

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Originally Posted by Chain View Post
1. Ctrl/cmd-click the RGB channel. (load channel as selection)
2. Add Vibrance adjustmeny layer.
3. Invert mask (cmd/ctrl-i).
That didn’t quite target just the really dark areas of the image I wanted for the desaturate of shadows only. Its probably real useful for targeting other areas.

Quote:
5. Hit cmd/ctrl-m to do a curves adjustment on the layer if I need to more narrowly attack a brightness range. Or use "blend if". Or another mask.)
That’s the key! I will say, building the black-like-channel like mask first is a bit easier as you can see what’s going on.

So far, I have a far greater control over this black-like-channel with the VC in Lightroom. When you convert to CMYK, at least initially, you are at the mercy of the conversion profile and as Lee had to do in his demo, pull curves on it. But you can only adjust what you got from that conversion on the true black plate. In LR (and ACR), there’s huge amount of control over creating this black-like-channel which I kind of like.

I think the technique has merit. But the idea is to produce channels of an idealized tone range and I’d personally like high bit quality data. Using the raw data itself from a VC seems like a neat and more modern approach. I’m not saying it can be substituted for the other 7 channels but I suspect for a lot of work, it can be. I need to keep playing.
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  #55  
Old 05-25-2011, 02:11 PM
creativeretouch creativeretouch is offline
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Re: Photoshop Channel concepts: The Power of Ten

Andrew, I would suggest to check Tony Kuyper's luminosity masks tutorial or saturation masks tutorial. I do not think you will be able to target various zones more precisely in any RAW converter.
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  #56  
Old 05-25-2011, 02:16 PM
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Re: Photoshop Channel concepts: The Power of Ten

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Originally Posted by creativeretouch View Post
Andrew, I would suggest to check Tony Kuyper's luminosity masks tutorial or saturation masks tutorial. I do not think you will be able to target various zones more precisely in any RAW converter.
Will do. I can say that thus far, I can target the tones for this black-like-channel with far greater control from raw than converting a copy of the original to CMYK and messing with just the black channel. And the profile used (its black gen) plays a huge role in what ends up on that black channel. The CMYK trick is a bit crude but does produce an after effect that looks better than the before. There is the rub, in nearly all these tutorials, the after has to look like an improvement for the effort. But which technique is best?
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  #57  
Old 05-25-2011, 02:27 PM
creativeretouch creativeretouch is offline
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Re: Photoshop Channel concepts: The Power of Ten

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Originally Posted by andrewrodney View Post
Will do. I can say that thus far, I can target the tones for this black-like-channel with far greater control from raw than converting a copy of the original to CMYK and messing with just the black channel. And the profile used (its black gen) plays a huge role in what ends up on that black channel. The CMYK trick is a bit crude but does produce an after effect that looks better than the before. There is the rub, in nearly all these tutorials, the after has to look like an improvement for the effort. But which technique is best?
You don't need to convert your image to CMYK. You can work in any color space you wish and create any luminosity selection & intersection you wish.
This technique is noiseless + you can paint on the mask as well ... It would be nice to have this possibility within RAW converter.
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  #58  
Old 05-25-2011, 02:33 PM
creativeretouch creativeretouch is offline
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Re: Photoshop Channel concepts: The Power of Ten

It would be nice to have Photoshop working directly with RAW images ...
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  #59  
Old 05-25-2011, 02:34 PM
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Re: Photoshop Channel concepts: The Power of Ten

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Originally Posted by andrewrodney View Post
That didn’t quite target just the really dark areas of the image I wanted for the desaturate of shadows only. Its probably real useful for targeting other areas.
It is a luminosity/brightness mask. And that is what you need to target the shadows. After step 5 it will target any range you want (like the shadows). Move the black slider to about 50 % to make the range similar to a K-channel (depending on the CMYK profile).

Your idea to create the mask information from the raw file instead of the 8-bit file will be like my method, but as you do have a few more bits of information in the raw file you might get a tad less noise and banding issues in the mask.
Since it's just for a shadow mask I believe the difference will be too small to notice, but definately worth considering.

EDIT: if you already have a 16 bit document i believe the trip to raw is not needed.

Personally I will go with the quicker method, but that being said, any of the techniques mentioned here for creating a luminosity/shadow mask can easily be automated down to one clik with an action, and they all provide good results for the purpose of a mask to desaturate shadows...
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Last edited by Chain; 05-25-2011 at 02:50 PM.
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  #60  
Old 05-25-2011, 02:36 PM
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Re: Photoshop Channel concepts: The Power of Ten

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Originally Posted by creativeretouch View Post
It would be nice to have Photoshop working directly with RAW images ...
Yeah, but you can add raw images as smart objects. That's pretty close at least.
(Doubleclick to edit the settings (camera raw pops up)).
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