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Fixing Gutter Brightening

What's that I say? Gutter brightening? What about darkening? Well, if you scan the way I recommend, you'll only ever get brightening, not darkening. Brightening occurs near the gutter (inside margin, where the paper is connected to the spine) and affects the areas that are supposed to be black so that they are quite a bit more luminous than they should be. Some scanners don't appear to get this effect at all; I'm quite unsure why. On the left is the most obvious brightened area (Creed's left shoulder; everything along the right panel border). The way to fix this effect is by using Quickmask with a soft brush to select the right side of the image, and then to use levels to darken the darks. Press the Q hotkey to enter and leave quickmask. I like to use a brush with 10% hardness. The size of the brush is determined in this manner: when you hold the brush over the image, the center of the brush should line up with the brightest part of the brightening (usually right on the panel border), and the left visible edge of the brush circle should hit the limit of visible brightening effect.

The picture on the left below shows how big the visible circle of your brush should be in proportion to the width of the affected area. (For one reason or another, cursors are not showing up in my screenshots, which is somewhat inconvenient). The middle picture shows a 175 pixel brush (the correct size for this image) with one click having been made.

On the right I am picking a size 175 brush with 10% hardness. Actually in my presets which you can find on a following page, I have three brushes of 10% hardness, of 60, 90, and 115 pixels. Otherwise I just use the [ and ] keys to shrink and grow my brush size.

I start making my quickmask at the bottom, clicking centered below the vertical line of the panel border. Then I move it upward by shift-clicking. (Or I start at the top and go down, depending. If you start in the middle you can get uneven coverage.)

Once my swath is painted, I press Q again to leave quickmask, and then invert the selection. (Inverse in the Select menu.) The above right image then looks like the following:

Now I bring up the levels dialogue, and input a Shadows value of 100.

	At 25%: the lightened area on the right	becomes darkened as it should be

After fixing the gutter brightening, examining Levels on the marqueed area reveals that the area that should be black is now mostly black. The editing steps that follow will mostly take care of the rest of the darkening by themselves. Alternatively, using 110 instead of 100 may work, but 100 should be fine.

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