Hi Larry,
Sorry for the long delay in our answer.
As for inserting images in your posts here, I advise you to use imageshack (
http://www.imageshack.us/). It is easy and works very well. You upload your image and they give you an url that you can use here, when composing your message.
The problem with your image is that it has zero pixel values. The generated background models (both DBE and ABE) also have zeroes, as one might expect.
If just
isolated pixels had zero values in your image, then there is a high probability that the interpolated models would have no zeros at all. However, your image has an extended area with constant zero pixels at the upper right corner, which is necessarily reproduced by background models.
This is the explanation of what happens with PixelMath in PixInsight LE:
When you divide your image by one of those models, some divisions by zero occur. PixelMath assigns an "infinite" value (actually, the highest possible value in the range of IEEE 32-bit floating point) to those pixels that get divided by zero.
Finally, when PixelMath rescales the resulting quotient image, the "infinite" pixels cause a total lack of accuracy.
Solution:
Add a very small number to your image before generating the background model. For example, use PixelMath to add something like 0.001 (create a new row in PixelMath, select the ADD operator, set R=G=B=0.001, and select no image as operand; then disable the Rescale option). In this way you'll have no zero pixels in your image, and the extra 0.001 won't harm it.
Another option is subtracting the model instead of dividing. This is what you should do if what you are trying to fix with background modelling is caused by additive phenomena, like light pollution. Adding the model should not have any problems with zero pixels.
With ABE, the corrected image is not as odd as is with PixelMath in PixInsight LE's DBE. This is because ABE is smarter than LE to divide images.
The same is true with the new PixelMath in the PixInsight Standard application, which I encourage you to use. By the way, Carlos has implemented ABE as a process in the PixInsight Standard platform. Using it within the new GUI is a delight.
Hope this helps. Please let me know.
