When it comes to that Background Eraser? 
The keyboard spacebar is your new best friend!


Never Never Never

Never switch back over your regular eraser for any erasing when you are using Background Eraser.


Always Always Always
Press your SPACEBAR instead.
 You have a special regular eraser built right into your Background Eraser via the spacebar.

Always use the spacebar.  Then you won't ever screw up any of that background data you just might want to retrieve later.

How cool.
How really cool.




 When you use the Background Eraser
and you want to:

1. Erase something unconditionally?
2. Unerase something unconditionally?

Then you should use your spacebar with the Background Eraser instead of switching to the regular Eraser tool. This is particularly significant for item 2.

OK, but why?

The Background Eraser is actually cleverer than it seems. Sure, it decides what is object and what is background and then erases background. But it also does something else. It subtracts the background color from the object color that is left behind. This gives you cleaner edges, uncontaminated with background color. The range of colors over which this happens depends on magic stuff happening in the brush, but is also affected by the Softness control.

But what's it got to do with switching tools?

While the Background Eraser tool is active it has access to the original image colors. If you unerase (right-mouse or spacebar-right-mouse) the tool can always restore the original image colors.

However, when you exit the tool the original image information is discarded and the image colors are replaced by colors that result from subtracting the background colors. (These are the same colors that appear on the screen while using the Background Eraser, the original colors being kept stashed temporarily and invisibly.)

Where there is a lot of transparency, the colors can become really strange as a result of subtracting the background color. Now, if you use the regular Eraser the results look really weird.

Where do you set the tolerance for the background eraser?

Look in the tool ribbon. The first "tab" (I forget the official name) contains Shape, Size, Hardness, Step, Density, Thickness and Rotation. (Defaults should be Shape = any, Size = any but I don't recommend below 25, Hardness = 100 (yes, really), Step 5 (higher and you don't sample image colors often enough, lower and the brush is slow), Density = 100, Thickness = 100, Rotation = don't care. The second "tab" has Opacity, Tolerance, Softness, Sampling, Limits and checkboxes for AutoTolerance, Sample Merged and Ignore Lightness. Opacity should be set to 100. Normally, you should check Auto Tolerance. The brush will automatically determine the best tolerance from the colors under the center of the brush. Though greyed out, the Tolerance control will update so you can use the number there as a starting point for manual adjustment. Softness should be normally left at 30. The Softness affects an automatic computation of edge softness based on color difference. If you have an extremely small color difference between object and background setting this control to less than 30 may improve separation. If the edge of the object resembles a broad gradient between colors, increasing Softness may be in order. Sampling Once means the sampling is done at the start of the stroke only. This is useful with a uniform background and allows you not to be careful about following object edges. Continuous is obvious - sampling throughout the stroke. BackSwatch and ForeSwatch use the respective swatches in the Material Palette for the definition of the color to be erased. Limits Discontiguous means that you erase background wherever it exists under the brush and is useful for objects with internal holes. Contiguous means that the background color will be erased only where it forms a continuous connection to the center of the brush. This tends to preserve object edges better than Discontiguous and is recommended when the color inside an object is similar to the background color. Find Edges is useful if the object and background color are similar. Additional edge information is used by the brush and object edges can be localized better. However, the price might be that the edges are a little sharp or distinct. Sample merged samples the background color not just from the active layer but from the entire merged image. Ignore lightness is a special setting that can improve the selectivity of the brush in certain cases. It is used when the object is very colorful and the background is unsaturated or the converse. If your image has heavy JPEG artifacts this setting may well detect and reveal block edges in your image.

If I were you I would change the order of the "tabs" in the tool ribbon, setting the second one as the leftmost. You will be adjusting all but the Opacity on the second "tab" fairly frequently. Size is about the only thing you would normally change on the first "tab". Right now the default organization of the tabs is so that the tool ribbon for all brushes looks alike. Programmers like this sort of consistency, However, on 800 x 600 it kind of hides the most useful part of the controls for the Background Eraser. That's probably where yours went. -Kris

backCopyright Camp Ratty ©2003 All Rights Reservednext page