Magic Wand tool tolerance setting

Question

I have looked all over the net and can't seem to find a definitive answer to the tolerance setting for the magic wand tool.

Let me explain:

Say I have the magic wand tool active and set the tolerance to 20. Now when I click in the image i get a selection pattern based upon that tolerance setting. And I know that the higher the tolerance setting, generally, the larger the resulting selection. I also understand how the "contiguous" and "sample all layers" check boxes affect the resulting selection. What I am wanting to know is this: exactly how does the tolerance setting affect the selection.

For example, again, let's say I have a tolerance setting of 20 and when I click on the image I click on a pixel that has the color #efb7b6. How does Photoshop use the tolerance setting to determine what other pixels become part of the selection. Does Photoshop then select all colors that are within 20 points of each of the Red, Blue, and Green portions of that color. For example, do colors FFb7b6, efCBb6, and efb7CA get selected because they are within 20 points of the base color but colors efCCb6, and dfb7CB don't get selected because they are not within 20 points of the base color.

What's the deal on the tolerance setting for the magic wand tool???

Thanks,

Warren

Terri Stevens · Accepted Answer

The whole thing just makes more sense when talking RGB values instead of hex. Not right or wrong... When working with images you want to use the RGB values. You slowly train yourself to see color casts in the numbers. Over time RGB will be very valuable to you.

I would say HSL is probably even more useful than RGB for understanding the magic wand tolerance. This is because by tolerance Adobe is really talking about luminance or how bright a pixel is. A tolerance of 20 means that when you click on a pixel with the 'sample size' set as 'point sample' then all contiguous pixels with a luminance of +20 through to -20 of the pixel you clicked on will be selected, with the luminance being calculated as the average luminance of the red, green and blue channels for that pixel. This is why the maximum tolerance can only be set to 255 as 8 bit images have 256 greyscale luminance levels. It's unwise to use hex colors as they are color model dependent.

c.pfaffenbichler · Answer

If you stop bothering with that manner of numbering colors and use proper RGB values it may appear clearer.

Quote from the Reference:

Tolerance Determines the color range of selected pixels. Enter a value in pixels, ranging from 0 to 255. A low value selects the few colors very similar to the pixel you click. A higher value selects a broader range of colors.

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