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superfrasky 01-17-2006 07:27 AM

Complex hair selection
 
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Hi friends. Im trying to make a perfect selection this image. The image was shoot with chroma background (blue). I need remove background (blue) but I can not remove blue highlights in hair. I have primatte chromakey (digital anarchy) but dont remove spill (blue) in hair. Anyone know a good method?
Thks

byRo 01-17-2006 07:50 AM

I would convert to LAB mode and have a look at the A and B channels.
Duplicate the layer and run levels on one (or both) of the channels marking a black point on the background and a white point on the hair.
You should be able to make a pretty good mask combining these two channels.


meok 01-17-2006 12:00 PM

Hi
This is how I would approach this: http://byloc.com/hair-extract.jpg

1. Original Image
2. Mask made using calculations. (Multiplied the inverse of an enhanced red channel into an enhanced blue channel.)
3. Result of applying that new alpha channel to the hair, we can clearly see the blue highlights.
4. Mask made with calculations by substracting the blue channnel with the red.
5. Result after using that second alpha channnel to mask a level (or curves) ajustment layer that subdued the blue cast.

Note that you can get much much bettter result if the file has better resolution and less jpeg artifact that the one that was posted. Hope this helps, good luck!

superfrasky 01-17-2006 12:39 PM

Quote:

Originally Posted by meok
Hi
This is how I would approach this: http://byloc.com/hair-extract.jpg

1. Original Image
2. Mask made using calculations. (Multiplied the inverse of an enhanced red channel into an enhanced blue channel.)
3. Result of applying that new alpha channel to the hair, we can clearly see the blue highlights.
4. Mask made with calculations by substracting the blue channnel with the red.
5. Result after using that second alpha channnel to mask a level (or curves) ajustment layer that subdued the blue cast.

Note that you can get much much bettter result if the file has better resolution and less jpeg artifact that the one that was posted. Hope this helps, good luck!

Great work meok, but I dont understand step 2 and step 4, anyone can explain it more in detail?

superfrasky 01-17-2006 02:37 PM

I need help.... I can not remove blue background and blue hair highlights....HELP, HELP,HELP
:cold:

Cameraken 01-17-2006 03:04 PM

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Hi Superfrasky.

Meok provided a great method which works fine on this picture. However there is perhaps a more useful method here which works on most images.

http://www.russellbrown.com/tips_tech.html

And Larry provided a great explanation here

http://www.retouchpro.com/forums/photo-compositing/11544-extraction-new-background-new-trick.html

Larry painted out the colour Before the extraction but it can be done after with a layer set to colour and applying the same mask. It can look more natural if you add some colour from the new background.

Hope this helps.

Ken

superfrasky 01-17-2006 04:10 PM

thks cameraken, but meok method I think that is good for this image. the problem is that I dont know how make him (2 and 3 step of method)

Cameraken 01-17-2006 04:39 PM

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Hi Superfrasky.

I think Meok must have a few extra steps. I donít really understand calculations.

OK. Iíll try and learn with you.

Dupe the Red Channel
Dupe the Blue Channel

On the Red Copy Channel adjust levels
0 1.00 172

On the Blue Copy Channel adjust levels
0 1.00 213

Select Image > Calculations

Source 1
Channel Blue Copy

Source 2
Channel Red Copy Invert Checked

Blending Multiply

Click OK

This makes a new Channel, Alpha1
Image > Adjust > Invert
Adjust Levels
30 1.00 192

This gives something very similar to Meoks Second Picture.




Ken

aztek1020 01-17-2006 05:12 PM

are you using photoshop or paintshop pro?

Swampy 01-17-2006 05:57 PM

2 Attachment(s)
This was a challenge, but here's what I came up with.

Basically did a H/S to put some more color in the hair first.

Used the red and green channels combined (see the great calculation tutorial above, Thanks, Ken!) to generate a mask

Inverted the mask and deleted the blue background.

Used Photoshop's Color Replacement tool (Under the Heal brush) to replace any remaining blue spill. You can go back into Curves and soften the whole thing to more closely restore the ash blond (original) colors.

This looks best on a dark background.


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