NormalizeScaleGradient 1.4.3

jmurphy

PTeam Member
Jun 13, 2010
306
141
Basingstoke, England
... the photometry graph is the diagonal you expect but there are no outliers/spread from the diagonal. Not sure what this is telling me about the star selection within NSG + my frames. I guess that means that the frames are good / star selection choices available are good quality?
If the photometry graph has no scatter, and the gradient graph is perfectly horizontal (no scatter), this means that the reference and target image you are comparing are identical. Somehow you have duplicated some of the images. Try selecting a different target image - you should then see the graphs you were expecting.

I did complete the process through image integration for the OSC image and compared it to the integrated image for the same mosaic pane created by WBPP. I was surprised that there was more visible gradient across the frame from the NSG image than the WBPP integration as I was not expecting that result.
NSG is not designed to remove the gradient. Instead, it removes the relative gradient between the chosen reference and the target images. The integrated image's gradient should be very similar to the gradient in the reference frame. If you wish to minimize the gradient, you need to use the image with the least gradient as the reference.

The main advantage of using NSG is to improve ImageIntegration's data rejection, and to determine more accurate (brightness) scale and image weights. Note that all normalized image will have approximately the same gradient as the selected reference frame.
 
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cyendrey

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Sep 21, 2020
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If using a narrow band filter with an OSC camera, some of the color channels may end up having little or no data. For example, a Ha filter would result in no data in the green and blue channel. This could cause NSG trouble, so in these cases it is necessary to split the RGB image into separate channels. If a filter is used that does not create dead channels, NSG can then process the RGB image.
OK, I think I understand. However, when I think of a NB filter for an OSC camera, I'm thinking more along the lines of my Optolong L'Extreme or the equivalent from other providers. It does not result (so far at least) in an image with zero or little data on a particular channel although some targets do slant heavily to the Ha end. In the frames I was testing with, (Eastern Veil nebula), the ZWO ASI2600MC-P w/L'Extreme resulted in good images on all channels, although the B has a higher noise level.
 

cyendrey

Member
Sep 21, 2020
13
0
If the photometry graph has no scatter, and the gradient graph is perfectly horizontal (no scatter), this means that the reference and target image you are comparing are identical. Somehow you have duplicated some of the images. Try selecting a different target image - you should then see the graphs you were expecting.
Ahhh, the light slowly dawns... ;-)

When NSG popped up the dialog box asking for a target selection, I just assumed it was asking about the target image I had selected for reference. So, I've now 'corrected' that and have checked photometry slope (looks like the demo image) but specifically checking the gradient slope for two frames - one I know was 'selected' in the NSG ImageIntegration (Capture.jpg) and one that I'm fairly certain was excluded from the NSG ImageIntegration (Capture2.jpg) I'm running NSG to Integration again just to make sure I'm correct on this. I do notice significantly different looking gradient slopes between the two frames.Capture.JPG

Capture2:
Capture_2.JPG
 

jmurphy

PTeam Member
Jun 13, 2010
306
141
Basingstoke, England
NormalizeScaleGradient 1.4.3 beta

Improvements / bugfixes:
  • The console summary text is now sorted by filename or weight
  • Input image formats are no longer restricted to only .xisf and fits
  • Fixes a possible integer overflow error if the input images are in integer format. The images are now converted to floating point.
  • The ImageIntegration ESD auto settings now uses the default ESD settings (outlier fraction = 0.3). The previous settings were preventing ImageIntegration from rejecting the bloated edges from stars with poor FWHM.
 

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