Quick Mask leaving "paint artifacts" outside the marching ants

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Jul 13, 2004
I’m new to Photoshop (as you will soon be able to tell), I’m using CS and I’m trying to cut a group of people out of a background using Quick Mask – following the manual and various tutorials I found. After much time spent, I got the “marching ants” just around the people that I wanted – I thought I was all set… But when I pasted the people onto a while background, in some spots, – outside of where the selection (marching ants) was I saw some black “artifacts” for lack of a better word that looked like some of my “red painting” – when I was painting to select more of the image for the mask. It seemed the places I went over several times (and had lots of red) might be where I’m seeing it. (I wish I could post a picture to show you).

Is this enough of a description for someone to help me out? In summary, things were showing up outside the marching ants selection – how can that be?


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Jul 13, 2004
The settings for the brush tool you use in Quick Mask mode can affect the quality of your mask, Dave. For starters, I typically use a hard-edge, rather than a soft-edge brush. Areas where brush strokes appear to cover sometimes aren’t fully opaque where soft edges overlap.

Also check the "spacing" setting of your brush tip shape. If it’s set too high, your brush will appear to be laying down a series of circles, rather than a smooth stroke. (Actually it IS setting down a series of circles, but the spacing controls how close together they run. This can be useful if you want to paint polka dots!)

Finally, it is always helpful to work at AT LEAST 100% resolution when painting a mask.
Jul 13, 2004
Here’s something to try…, after using the Quick mask mode to obtain your selection, save the selection as an alpha channel (selection > save selection).

Switch to the channels palette, and clike the eyeball in front of the saved channel, everything will turn to black and white.

Now, it’s real easy to see what got selected and what didn’t. Paint with black to remove those white spots that acidently got selected, paint with white to remove the black spots that didn’t get selected but should have been.

Once you’ve got everything right, control click the channel, then click the eye in front of the RGB channel, turning all the colors back on (and, removing the eye in front of the alpha channel), then switch back to the layers palette.

BTW, this lesson is included in the Photoshop CS Classroom In a Book — lots of structure lessons to introduce someone to how to use Photoshop… It’s published by Adobe Press.

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