Wispy Hair: knockout or overprint
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Tip #105
Wispy Hair: knockout or overprint
Ken Church wrote to get help with masking hair...
"I'm trying to find out if there is a technique in photoshop that utilises both masks and clipping paths to allow fine wispy hair to overprint a colour background while still knocking out the colour behind the main part of the picture. Do you know if this is possible and where can I go to find out how it is done? PS This is my first vist to your great web site
Fred sez:
I'm thinking you don't want to "overprint" and "knockout" at the same time (since they are very opposite techniques) but would rather do it with color replacement.Overprint: is when an image is actually printed on top of another. In printer terms this is a "surprint".
Knockout: is when an image is reversed (or "knocked out") of an existing image. The 'hole' becomes white, or the color of the paper. Knockout/put back uses the original shape which was reversed out and puts it back into the hole. The technique allows an overlaying image to sit on fresh paper rather than another image.
It would be difficult indeed to create a knockout/putback of wispy hair in a model shot. We consulted our resident photographic retouching/manipulating expert on this:
Joe Kling sez:
I will work on the assumption that Ken has a pretty model with wispy hair (that you see glints of the (white?) background through the hair) He wants to put her onto a color background while keeping the same, wispy feel to the hair. He also needs to make sure that where there is solid parts of the body, the background color is completely knocked out.
Using the term "overprint" here could get somebody in some "spensive" trouble.
Color Replacement is definitely the most direct route to take IF the background is all one color, like a "sweep" or "flat" behind the model.
If the background is more complex, you're in for some rather ntricate Masking of the complex subject away from backgrounds. It's way beyond the scope of this column however if you read Macworld magazine, take a look at Deke McClelland's masking how-to in the February '98 issue (pg 119).
Fred sez:
Deke also goes into the technique in great detail in his Photoshop 4 Bible book. Take a spin over to graphic-design.com/bookshelf/ and pick up a copy.
By the way, Joe is building a full scale online Photoshop Photo Retouching seminar for the Design Center and we'll send Ken a copy of Joe's third week lesson module which deals with this exact issue.
See: Follow-up in Tip #106