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Frequency separation via channel mixer

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Old 06-11-2012, 05:36 AM
Der_W's Avatar
Der_W Der_W is offline
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Location: Germany
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Frequency separation via channel mixer

Hi everybody,

I was asked to give a little background information about my frequency separation via channel mixer action (, so here it is .
I hope things won't get too complicated, if you have any questions, just ask me!

The whole idea of the concept was to create a dynamic frequency separation where the high pass will be automatically created based on the low pass.
All the arithmetic that we do will be done in the individual color channels, therefore the end result will be luminosity only (so far I haven't found the time and motivation to think about a better approach that'll work for color in the same step as well).

To begin we're going to duplicate the background layer and chose "Image"-"Adjustments"-"Desaturate". Immediately after this we go to "Edit"-"Fade"-"Color". Why do we fade this step to "Color" mode? Because we want to be left with just the luminosity and "Color" is the opposite of "Luminosity".
Put this layer and all the following into a group and set the group's mode to "Normal".
Next we duplicate the desaturated layer again, convert it to a smart object and blur it. The next step is a little trick. To save the blurry image in one channel and the high pass in another channel, we're going to use the advanced blending options and uncheck the channel blending for the R and B channels.
Now we need to create the according high pass for our blurred layer. To do this we create a new channel mixer adj. layer, go to the blue channel and chose 50% Red, -50% Green, 0% Blue and 50% Constant. Why that? Well if you remember the settings we use for the "Apply Image" based high pass, you'll notice that we subtract the layers from each other, then halve the result and add 128 to the mix. We're just doing the same with our channel mixer .
Now that we have our low pass and our high pass layer, what we need to do is work with it.
To do this, create two new blank layers. Call the first one "Low Pass Work", the second one "High Pass Work". On the "Low Pass Work" layer go to the advanced blending options again and uncheck blending for the R and B layers (just like we did for the blurred layer, remember?). Now go to the "High Pass Work" layer and uncheck blending for the R and G layers (why? Because we used the channel mixer to create a high pass in the blue channel!).
As a next step we're going to add our high pass and our low pass channels back together into one channel. I'm just going to use the green channel for this.
To do this, create another channel mixer adj. layer, in the red channel add a Constant of 50%, in the green channel add 100% blue and in the blue channel add a Constant of 50% again. Now blend this layer in "Linear Light" mode. This will add just the blue channel (high pass) into the green channel (low pass) and create our composite channel.
Now the red and green channels are okay, but the blue channel still contains the high pass, so what we can do is simply add yet another channel mixer adj. layer, set it to "Monochrome" and use 100% green channel.
Now while the group is set to "Normal" mode you can work on the "Low Pass Work" and "High Pass Work" layers however you like it, change your initial blur radius (the work layers won't automatically update to the new radius, so keep that in mind!), add a curves adj. layer on top of the work layers and change the blue channel's contrast to sharpen your image or do whatever else you want to do with it .
When you're done working with the split, set the group's mode to "Luminosity", so the color will come back. Or if that sounds like too much hassle, just put the group underneath all your other layers, place them in yet another group and set this group's mode to "Color". That way you won't have to change the group's mode when working, but you can't work with luminosity information in the top group anymore.
I've attached actions to do both and also another possibility that'll just place a copy of the existing layers on top of the group with the blending mode set to "Color".

I hope this idea is helpful for you in any way, if you have any questions, just let me know .

PS: For those of you how tried to follow along with the action and wondered, why the "B + G" layer is a little different than explained here, I found out that creating the "Linear Light" mode in the channel mixer itself made the action a little more accurate, so I did that. Since "Linear Light" works like: C = B + 2 * A - 1, it was easy enough to do this instead of using the actual built in blending mode.
Attached Files
File Type: zip Frequency Separation Channel (1.3 KB, 106 views)

Last edited by Der_W; 06-11-2012 at 05:45 AM.
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Old 06-11-2012, 07:38 AM
Chain's Avatar
Chain Chain is offline
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Join Date: May 2009
Location: Oslo, Norway
Posts: 540
Re: Frequency separation via channel mixer

That... That's amazing.

We need people like you!
I am adding this to my action sets immediately to test some more.

I made a slight alteration - a version that adds a "band stop"-layer in the stack. For those of us who sometimes like quick and dirty fixes... I didn't put much effort into polishing my alterations.
I usually use Surface Blur for my separations as i find it useful near edges, but didn't add it to the action as it is a damn slow filter.
Attached Files
File Type: zip Frequency Separation Channel (1.3 KB, 70 views)

Last edited by Chain; 06-11-2012 at 08:22 AM.
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Old 06-12-2012, 11:38 AM
ashphotoart's Avatar
ashphotoart ashphotoart is offline
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Join Date: May 2008
Location: India
Posts: 301
Re: Frequency separation via channel mixer

I can see how advnaced are your method... still figuring how it can be work in fly its unbelieveable superb method.... Thank you very much for sharing ur knowledge.

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