This Photoshop is driving me crazy
February 23, 2010 8:00 AM   Subscribe

PhotoshopFilter: The Magic Wand tool seems to be selecting too much, even when the tolerance is set to zero. What gives?

I don't remember this being the case in the past, but I'm recently noticing that whenever I try to magic wand an area, it will be overzealous in selecting regions. Let's say I have an object on a solid white background and I'm trying to select out the white and remove it so the object is on a transparent background. I use the Magic Wand tool, turn the tolerance to zero and check "Contiguous," then select. So far so good, right?

Not always. It seems to depend somewhat on how close I click to the object. The closer I am, the more it includes in the selection-- so if I have any edges of the object that is fairly light, all of that gets selected. Normally it's not a problem if I click far enough away. But if there are small areas or "holes" in the object, sometimes shift-clicking in there to add to the selection will just add too much. If the hole is small enough, the magic wand pretends the edges aren't even there! Keep in mind that tolerance is still zero (so it should ONLY be selecting pixels that are the same color) and contiguous is checked (so it isn't selecting other pixels that are the same color that are not attached).

What gives? Did I turn on an option I didn't know about?

(I'm on CS3, Mac.)
posted by lou to Computers & Internet (8 answers total) 3 users marked this as a favorite
A couple quick questions:

Are you using the Quick Selection Tool or the Magic Wand? The Quick Selection Tool will have a disk-shaped selection area (the size can be adjusted with the usual Brush picker dialog) - I tend not to use it, but it's the default tool in CS 3.

Also, is "Sample All Layers" checked or unchecked?
posted by ardgedee at 8:09 AM on February 23, 2010

Are you in the wrong layer and maybe the layer you're in is uniform?
posted by If only I had a penguin... at 8:19 AM on February 23, 2010

I'm only working on one layer, and it's definitely the Magic Wand tool. (I don't use Quick Selection much.)
posted by lou at 8:21 AM on February 23, 2010

Do you have "anti-alias" checked?
posted by misterbrandt at 8:21 AM on February 23, 2010 [2 favorites]

Trash your PS prefs and fire it up again, see if the behavior is as you expect.
posted by cjorgensen at 8:32 AM on February 23, 2010

Are you working on a jpeg image when this happens? If you zoom in close to edges in jpeg images, you'll see a lot of junk pixels. It's part of that format's compression.

Is it possible for you to provide an image where you're having this trouble, metamail me if you want, and I'll see if I can duplicate it?
posted by royalsong at 8:33 AM on February 23, 2010

Iirc you can choose on what basis the selection tool works. It might be set to "similar brightness" or "similar RGB" or one of the other settings. Is "feather" still an option? Check that too. If you have already removed the background (I see you mention transparent) it might be tiny islands of white pixels that remain, and while you can't see them the tool can.
posted by Iteki at 10:24 AM on February 23, 2010

It's not anti-alias, it's not jpeg artifacts, it's not feather. I understand the description of the problem is a little hard to understand given that there's no visuals to accompany the question.

Anyway, I did a little more digging around and eventually found the problem. It turns out that the eyedropper tool's selection options have an undocumented relationship to the magic wand. If you right click with the eyedropper tool, you can choose to select a color that is the average of some radius of neighboring pixels. If you choose anything other than "point sample," say, "11x11 area" which is what I had, then switching over to the magic wand would cause it to select based on that area average. That's what was causing my unexpected behavior.

Anyway I switched it back and everything works now.
posted by lou at 3:31 AM on February 25, 2010 [2 favorites]

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