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Difference layer mask

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  #41  
Old 01-02-2012, 09:56 PM
Eikon Eikon is offline
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Re: Difference layer mask

Quote:
Originally Posted by Flashtones View Post

One can be made without calculations as such.
Go to the channels pallet and CMD+Click the composite channel to select the luminosity.
Hit the new channel button at the bottom of the pallet to create an alpha channel based on this luminosity.
Select the new channel to make it active. The original Luminosity selection should still be active, and now fill that selection with black.
I wa reading the same dave hill thread with the missing mr.randall links and went in search of how to create a difference mask. The above appeared to be the solution but i couldnt get it to work. So let me see if i have this right...

First off, unless im a damn fool, im cs5, ctrl clicking selects the layer contents, not the luminosity. Apparently to do that, the new shortcut is ctrl+alt+2.

With that selected, clicking the new channel button gives me black, not a luminosity based alpha. To create a new channel based on this selection you must either...
a) ctrl click the new channel button & invert that new map, or...
b) select -> save selection, create new channel

With that done, and the original lumi selection still marching, filling that selection with black doesnt work... At least not via the paint bucket. You can press delete to bring up the fill option and select black, and that will fill with black properly.

This apparently finally gives you the magical differnce map... Cept, is it? Its a black and grey map, no white... Is this what we want? If you open up levels on this new channel you see all the info is over on the left. If we drag the white slider over to the edge of color range, the we get a full white black and shades of grey map. But again, is this what we want? Using this "full range" version as a curves mask will give different results than using the original black and grey version.

So thats my question... Just wondering which is the INTENDED way to use the difference map.

Thanks all.
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  #42  
Old 01-03-2012, 12:37 AM
John Wheeler's Avatar
John Wheeler John Wheeler is offline
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Re: Difference layer mask

Hi Eikon

As always, my posts are all just IMHO.

In reading the whole thread, the search for the Holy Grail of the Difference Mask was much like a solution in search of a problem.

Sometimes it is much easier to describe what you would like to achieve (as was eventually done in the thread) and come up with ways to achieve a solution to that problem.

From my best understanding (because it jumped around a bit) this was in search of a midtone mask. You are correct that the approach mentioned in the thread that you repeating in your post does not have a mask that reaches all the way up to white. So if you want an adjustment Layer to be able to have full effect that Layer Mask created as you indicated would have to be adjusted.

Murray indicated an much easier way to create a midtone mask and that was with the Color Range tool and selecting midtones. All of the neutral color tones in the Color Range are based on Luminosity. Once the selection is made it can be converted directly as a Layer Mask or saved as a Channel. If this Mask/Channel does not transition as desired it is a simple change with a Levels or Curves adjustment.

IMHO there was a lot of focus on Robert Randall's difference mask approach. From all that I have read about Robert Randall his approach is more along the lines of having an image, knowing what he wants to change, and then with a deep understanding of how all the different Photoshop tools, blends, etc he uses (or invents on the fly) the approach that achieves what he intends to change. It may sound subtle yet I think it is significant. He is "what do I need to change" centric vs "what can this tool do for me centric."

Everyone has an approach that best works for them and if you want a midtones adjustment mask (which I think is the bottom line of the thread) then Murray's approach is the easiest without having to create extra channels, selections, adjustments, calculations, or angst. Hope this was helpful.
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  #43  
Old 01-03-2012, 07:54 AM
Eikon Eikon is offline
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Re: Difference layer mask

i gotcha john. not saying i was trying to be rob randal or anything. i was just reading a thread which lead me to the question of whats a difference mask, and how can i make one. i use highlight and shadow masks all the time, but since the process flashtones outlined didnt work, that got me MORE determined to figure out what it was and how to make it.

and ya, i realized you could do it with color range, but think i also read something like 'you get better, more subtle results if you do it this way'. so i wanted to create the mask both ways and see which was better.

anyway, ya it was helpful. ultimately i was not looking for someone to handhold me in PS. iv been doing it long enough and usualy know how to get the look im after. its just something id never heard about and figured there was an opportunity to learn!

thanks for the insight.
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  #44  
Old 01-03-2012, 08:38 AM
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John Wheeler John Wheeler is offline
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Re: Difference layer mask

Hi Eikon
No intention to imply anything about robbing. Just trying to point out I think the difficulty of finding documentation on Randall's difference mask approach increased the anticipation of value as if it were the Holy Grail (I. Obviously did not communicate well).

You duplicated the technique in the thread and got the same result that I also observed. I create difference masks an alternate way and for a different purpose. If interested I could add that to the thread as well.
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  #45  
Old 01-03-2012, 08:42 AM
Eikon Eikon is offline
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Re: Difference layer mask

sure john... might as well! the more methods the merrier.
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  #46  
Old 01-03-2012, 08:53 PM
Flashtones Flashtones is offline
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Re: Difference layer mask

Quote:
Originally Posted by Eikon View Post
I wa reading the same dave hill thread with the missing mr.randall links and went in search of how to create a difference mask. The above appeared to be the solution but i couldnt get it to work. So let me see if i have this right...

First off, unless im a damn fool, im cs5, ctrl clicking selects the layer contents, not the luminosity. Apparently to do that, the new shortcut is ctrl+alt+2.

With that selected, clicking the new channel button gives me black, not a luminosity based alpha. To create a new channel based on this selection you must either...
a) ctrl click the new channel button & invert that new map, or...
b) select -> save selection, create new channel

With that done, and the original lumi selection still marching, filling that selection with black doesnt work... At least not via the paint bucket. You can press delete to bring up the fill option and select black, and that will fill with black properly.

This apparently finally gives you the magical differnce map... Cept, is it? Its a black and grey map, no white... Is this what we want? If you open up levels on this new channel you see all the info is over on the left. If we drag the white slider over to the edge of color range, the we get a full white black and shades of grey map. But again, is this what we want? Using this "full range" version as a curves mask will give different results than using the original black and grey version.

So thats my question... Just wondering which is the INTENDED way to use the difference map.

Thanks all.
Not sure what the problem is. I'm using CS5 on a mac and my steps work as stated. CMD+Clicking the composite RGB channel is exactly the same as CMD+OPT+2.

Sorry I can't explain why it works on my system and not yours. Maybe you could pose the question on the Adobe board, but I suspect you are doing something wrong. Are you sure you're clicking on channels and not layers?

Anyway, ultimately a mask of blacks and grays is fine; that's the subtlety, that was noted, in play. If your adjustments through that mask aren't strong enough just duplicate the adjustment layer as many times as needed for added strength. Or, adjust the mask with levels, etc, to suit your needs.
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  #47  
Old 01-03-2012, 09:04 PM
Eikon Eikon is offline
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Re: Difference layer mask

Not to worriec about it. Maybe its a pc thing? I dont recall if i tried it with clicking the rgb channel, or just the layer. I probably tried it both ways since i read your description over and over and over to try and figure out why it wasnt working as described.

Anyway no prob. We all get there eventually!
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  #48  
Old 01-05-2012, 01:27 AM
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John Wheeler John Wheeler is offline
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Re: Difference layer mask

Hi Eikon

Per our previous discussion, following is the images and mask used where the key ingredient in creating the mask was using the difference mode blend. I did this in a post about 6 months ago in another forum. I received permission to post the original image on RTP from its author Shawn Rakestraw at http://www.pixelrake.com/

Here is the original image:
Original.jpg

Here is the mask that I created using blend mode as a key ingredient:
Difference-Mask.jpg

Using that mask I replace the background as an example:
Replaced-Background.jpg

And here is the image and just using some adjustment layers with the mask:
Modify-Just-Sky.jpg

Here is the copy and paste from the other forum on the steps I took:

I usually make up the masking approach on an image by image basis and on the fly - enjoy the experimenting. I usually think in terms of how can I make the image parts I don't want black and the parts I do whan white. I wanted to get rid of the blues and the bright white clouds. Soooo
1) To make blue black
Stamped image; foreground to sampled blue sky; ;pencil tool to difference mode and painted one continuous stripe over area ~ horizon and above
2) Make White clouds black
Stamped another original image; foreground to sampled white clouds; pencil tool in difference mode and painted one continuous strip over area ~horizon and above; used curves adj layer (levels would work too) and moved white point for right balance with tree and snow on tree (won't be perfect)
3a) Combine 1 and 2 with blend (I used screen yet others work too)
3b) Used B&W adj layer to tweak the image to get right balance
4) Threshold to max just make black and white
5) Use "0" tolerance and Quick selection tool to pick up a few pieces of tree snow not picked up by above (I typically have a zero tolerance policy in regards to the Quick Selection Tool
6) Magic wand to give selection
7) Use intersection of this selection with all area above horizon
8) Move selection to mask
9) Use refine mask to add 1 px feather
-------------------------------------------------------
Difference mode blend was used in combination with several other approaches to create the mask I desired. Hope this is useful and thanks again to Shawn to use his original image.

Last edited by John Wheeler; 01-05-2012 at 01:32 AM.
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  #49  
Old 01-05-2012, 05:25 AM
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Chain Chain is offline
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Re: Difference layer mask

Original question has been solved (make a mask of the mid-tones). Discussion is venturing into interesting masks that can be made based on the results of the Difference blend mode -*perhaps worthy of it's own (less confusing) thread?

Just jumping in here to request that we stop using the confusing term "difference mask" (it explains nothing) and call it "mid-tone mask" or whatever is most explanatory. Or just "mask".

To me, the term "difference mask" could be applied to any mask that has been created as the difference between two layers. It doesn't specify what the mask actually is so I find it only serves to confuse.

Last edited by Chain; 01-05-2012 at 05:30 AM.
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  #50  
Old 01-05-2012, 07:28 AM
unimatrix001 unimatrix001 is offline
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Re: Difference layer mask

I understand that this thread has been solved but i found this awhile back from a photography site thought it might help clarify this question for new readers.
http://internet-retards.com/wpmu/pho...t-photography/
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