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Extracting Hue-selections as a Mask

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Old 03-29-2012, 02:41 AM
pmiles pmiles is offline
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Extracting Hue-selections as a Mask

I love the ability in the hue/saturation dialogue box to make custom hue-range selections with adjustable hue selection fades on either side. But occasionally I have found my self wishing i could have the custom hue selection ability from a Hue/Saturation layer in some of my other favorite adjustment tools.

The following is a description of one way of extracting the custom hue-selections from a Hue/Satuartion layer as a mask to use with other layers.

Setup (In this case with a single layer image)
- Duplicate the image
- add Hue/Saturation layer above it
- put the above 2 layers in a folder
- In the hue saturation dialogue box choose any layer other than Master (reds for example)
- set the hue rotation to 180 degrees.

Making the custom hue range selections.
- between the 'before and after' hue bars (the graphics at the bottom of the hue saturation dialogue box) grab one of the triangular hue-fader sliders and slide it all the way to the other triangular hue-fader slider.
- click the "eyedropper tool" above the before/after hue rotation bars graphic.
- move your mouse to your image and click the hue you want to select in your image.
For example a skin tone, parts of the face will be now be turned a cyan-ish color. (The hue-range selection sliders between the 'before and after' hue bars will jump to the hue you just clicked on)
- While holding the option key down (Mac), click other areas in the face that have not changed color until the whole face is cyan. ( the selected hue-range is indicted with a dark gray bar between the 'before and after' hue bars graphic. The dark gray region will grow wider as you add to your selection. I usually set the eyedropper to 1 pixel sample size when doing this)
- once all the skin tone is selected pull the little triangular hue-selection-fader sliders either side of the dark grey region out a bit to add a feather either side of the hue selection.
-leave the face cyan

Turning the hue selection into a mask
- change the blend mode of the folder containing the copy of the image and the hue/saturation layer to difference.
- Make a merged copy of the result to a new layer (command-option-shift-E (mac))
- desaturate the new layer 100%
- Use levels/curves to adjust the result as desired
- click channels pane and click "load channel as selection" icon
- Back in the layers window make a new curves adjustment layer. The selection will be added as a mask to the curves layer.
- delete the merged copy and the folder if it's no longer needed


Notes
Early days with this. Let me know if you find easier ways to do it. Maybe there are better settings in addition to the hue rotation setting i am using that would make a bigger difference between the two images larger so the difference mask would not be so dark.

Regards
Peter

Last edited by pmiles; 03-29-2012 at 02:48 AM.
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Old 03-29-2012, 08:03 AM
mistermonday's Avatar
mistermonday mistermonday is offline
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Re: Extracting Hue-selections as a Mask

I have been using a similar technique for a number of years. Instead of shifting the channel's hue to 180, drag the Saturation slider all the way to -100%. Use the same technique to compress the range by dragging the triangles together and making your selection with the + eyedropper tool. Instead of a colored selection you end up with a grayscale selection. You can raise the Brightness slider if you want to create more contrast.
The challenge with both your technique and mine is that it is very difficult to turn the resulting difference layer in a good quality mask. And that is unfortunate because the technique of using the Hue Sat adj layer to isolate a very tight color / color range is really the best that Photoshop has to offer. Even the newest version of the Select>Color Range command does not produce the same accuracy. I would think that it would be really easy for the Adobe programmers to turn the Hue-Sat adjustments into an actual selection but they never have.
Regards, Murray
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Old 03-29-2012, 11:12 PM
pmiles pmiles is offline
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Re: Extracting Hue-selections as a Mask

Thanks for that.
I have been having a go using imageJ software mentioned in the FFT thread to convert copies of RGB images I am working on into Hue Saturation and Brightness and saving result as tif. this has been to use the saturation layer as a mask. But maybe there is a way to use the exported Hue layer to select with. Hmmm...

Regards
Peter
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