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bulleteraser.gif What to do when too much is erased

Here are some ideas for coping with the situation where the Precision Background Eraser starts to erase some of your object. Assuming you are working with the default brush settings, then ideas are arranged roughly in the order you should try them.

  • Make sure you are working with an image that has high quality and good color definition. Try running the OneStepPhotoFix script on your image before starting work with the Background Eraser.If your object has no internal holes, try moving the center of the brush further from the object or reducing the Size setting of the brush.
     
  • Make sure you have not set a high value for Step. Try a setting of 5.  A high setting can lead to incorrect sampling of the background and erroneous erasing. Also confirm that Sampling is set to Continuous.
     
  • If the object has no internal holes, make sure you are using a Contiguous setting for Limits and not the Discontiguous setting. If you are already using Contiguous, try setting Limits to Find Edges.
     
  • Whether or not the object has holes, try to increase the Sharpness setting from the default of 70. If you have to go much above 90 then your object is probably the same color as the background in the problem region and you may have more success defining this area manually. As soon as you have sorted out the problem region set Sharpness back to the default setting or otherwise your erased edges may become unnaturally sharp.
     
  • When too much object is erased, don't drag the brush. Instead click near the object boundary and see what happens. Fine-tune the brush settings by undoing and clicking near the same spot with the new settings until you get what you want. Then continue clicking, not dragging, around the boundary. As soon as too much or too little is erased, undo the last click, re-tune the settings or change where you clicked in the background, and continue in the same way
     
  • If you have tried all of the above and even after this tweaking some of the object is erased, then let this happen. Now, without changing the tool settings, run over the erased part of the object with the center of the brush while holding down the right mouse button. There is a good chance that only the object will be unerased, leaving the background erased. If not all the object comes back, reposition the center of the brush on a remaining transparent part of the object and repeat the unerasing. Rubbing the brush back and forth in the immediate vicinity of the erased object region may also be helpful.
     
  • Consider making a selection of a problem area (e.g. with the Freehand Selection tool), inverting the selection (Selections > Invert) and then using the Precision Background Eraser. The tool will respect the selection and leave the now deselected problem region untouched for you to deal with later.

bulleteraser.gif What to do when not enough is erased

Here are some suggestions for dealing with incomplete erasing of the background by the Precision Background Eraser when you are using the default settings. They are only in very roughly the order you should try them since what works best will depend on the specific nature of your image.

  • Make sure you are working with an image that has high quality and good color definition. Try running the OneStepPhotoFix script on your image before starting work with the Background Eraser.
     
  • Ensure that your image is not excessively noisy or overly sharp. This can lead to single-pixel specks being leftover by the Background Eraser. In such a case try running Adjust > Add/Remove Noise > Edge Preserving Smooth at a setting of about 2 and no more than 4. This should suppress non-detail noise while preserving image edges and will give you cleaner results with the Background Eraser.
     
  • Make sure you have not set a high value for Step. Try a setting of 5. A high setting can lead to incorrect sampling of the background and erroneous erasing. Also confirm that Sampling is set to Continuous.
     
  • Make sure your Hardness setting is at 100 so that the brush erases completely even at the edges of the brush.
     
  • If there is a halo of different color left around your object edges, try moving the center of the brush carefully closer to the edge. Because of lighting effects, it is not uncommon for the color immediately next to an object edge to be rather different from the color of the background. By moving the center of the brush closer to the object you will be able to sample this different color. To better judge how close you are to the object you may find it helpful to check Use precise cursors on the Display and Caching tab of File > Preferences > General Program Preferences.
     
  • If there is a halo around your edges it may be because they are soft and gradual. In that case try decreasing the Sharpness setting. Decreasing Sharpness may also help if too little of your background is erased in general. However, you should be very careful with this since low Sharpness can result in your losing parts of your object.
     
  • If you have set Find Edges for Limits, then change the setting to Contiguous. If you are trying to erase internal holes in an object, choose Discontiguous instead.
     

The remaining suggestions concern removing the debris that can sometimes surround an object after erasing. This is most likely to happen with backgrounds that have a lot of fine texture or small scale color variation, such as grass or gravel. When the background varies in color so widely, some of the more uncommon colors in the background might be interpreted as objects to be kept. The result can be unerased specks several pixels (or tens of pixels) in size in the transparency surrounding the object. There is a range of straightforward ways of disposing of this debris.

  • When faced with a complex background, set a small brush Size and concentrate on erasing correctly very close to the object edges. Then set a larger Size and, holding Spacebar, erase the rest of the background that remains around the object.

  • If there are just a few persistent unerased specks surrounding the object, click the center of the brush on each speck instead of brushing around it. A small brush Size can make this more effective.

  • When you have a single object surrounded by disconnected specks, try this approach. After completing the Background Eraser work, change to the Magic Wand tool. In the Tool Options Palette, set the Mode to Replace, the Match mode to All opaque and make sure that Feather is at zero and both Sample merged and Anti-alias are unchecked. Now click on the main object. This object will be selected but none of the detached debris will be part of the selection. If you now do Selections > Invert, you will end up selecting everything other than the object, i.e. the debris you want to remove. Press the Delete key and - voila - the debris is gone.
     
  • If you have a multi-part object surrounded by specks, you can use the above technique and simply shift-click with the Magic Wand on the different bits of object to select them all in succession, finishing by inverting the resulting selection and deleting it.
     
  • A more complicated and less desirable technique uses the Remove Specks and Holes filter to deal with the debris. The basic idea comprises four steps: (1) convert the image transparency to a mask; (2) convert the mask to a selection; (3) remove the specks from the selection; (4) invert the selection to select only the specks, and then delete this selection. Even if you are not familiar with Paint Shop Pro masks, the procedure is simply a matter of following these steps exactly.
     

1. 

Finish the Precision Background Eraser work.

2.

Create a mask with Layers > New Mask Layer > From Image. A dialog appears. Make sure that Source window contains the name of the image you are working on and that Invert mask data is unchecked. In the Create mask from section choose Source opacity and press OK.

3.

Now make the selection with Selections > From Mask.

4.

We have the selection we want so we don't need the mask any more. The mask is still the active layer so delete it with Layers > Delete. A message appears asking Would you like this mask merged into the layer below it? Be sure to answer No.

5.

Remove the specks from the selection with Selections > Modify > Remove Specks and Holes. Set Remove Specks and then the set the size of the largest speck that will be removed. This will depend on the size of your image and the size of the specks so experiment while watching the preview. To cope with a very broad range of speck sizes the maximum size is specified as a variable number multiplied by a powers-of-ten multiplier.

6.

Do Selections > Invert to select the specks (and not the object) and press the Delete key.

bulleteraser.gif My Background Eraser is too slow

The Precision Background Eraser has to do many complex calculations including analyzing colors to determine what is object and what is background, computing transparency, and unmixing the background color from the object. It has to do this repeatedly at every step of the brush. In addition, it has maintain certain transient information beyond what is normal for an image layer in order to perform its operations efficiently. This level of complexity may make the brush slow on older computers. Since not everyone can afford to purchase the latest and greatest computer, here a few tips for improving the performance of the brush. They focus either on improving computation speed or reducing memory use. If you are going to be extracting only a small portion of an image - for instance, a person in a landscape or one person from a group - crop your image first to just contain all of the object and as little else as possible. This will reduce memory use and is quick and easy to do.
 

  • Consider purchasing more RAM memory. It is relatively inexpensive and almost all image editing operations will benefit from more RAM, not just the Background Eraser and not just Paint Shop Pro. More RAM is often more beneficial than a higher processor speed, especially if you see swapping of memory to disk.
     
  • Make sure you have enough free disk space to support a swap file at least double the size of your RAM memory and check that your Windows Virtual Memory settings permit this disk space to be used.
     
  • Close down unnecessary programs or open images to make more memory available for use by Paint Shop Pro.
     
  • Consider temporarily switching off the Undo system by unchecking Enable the undo system on the Undo tab of File > Preferences > General Program Preferences. This will eliminate some writing to disk and potentially reduce memory usage while increasing the responsiveness of the brush. Since you can always unerase mistakes in the Precision Background Eraser the capability to undo becomes less important.
     
  • The brush Size represents the diameter of the brush in pixels. When you halve the Size, the area of the brush decreases by a factor of four and the brush also becomes about four times faster. Working with a small Size can therefore do a lot to speed up your work. As long as you accurately extract the edge of the object, the remaining background surrounding the object can be erased quickly and easily. You can use Spacebar with the Precision Background Eraser, you can use the regular Eraser, or you can select the remaining background with a selection tool and then delete a selection. Using Spacebar with the Precision Background Eraser is the best approach, since in unconditional erase mode the brush becomes much faster yet still allows you to unerase any mistakes you make.
     
  • The Step determines how many times along the stroke the brush processes the image. Double the Step and you reduce the processing by 50%. If your object is very different in color from the background or the background is smooth because it is out of focus, you can consider increasing the Step setting from 5 to 10. Be prepared to reduce the Step again in busy regions of the image or if the quality of the result suffers.
     
  • When you are erasing an object with holes (e.g. sky from between the branches of a tree) it is not efficient to use a small brush because you have to laboriously click in many places within the object. Instead, it is much better to use a large brush with Discontiguous set for Limits, which erases large amounts of background in one go. You can make this large-brush process faster by clicking the brush at points around the object instead of dragging it around. Avoiding dragging prevents the same regions of the image being processed several times under the brush and makes things much faster. By choosing the background color of your click points carefully you can get rid of a lot of background very quickly with just a few clicks.

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