johnpane
Well-known member
I am getting horizontal color anomalies when I run DrizzleIntegration. The following example comes from the center of an integration of 59 color subframes of the Leo Triplet. The subframes were taken both before and after meridian flip and there was also some rotation due to polar alignment error, so all but the reference frame underwent significant coordinate transformation prior to integration.
All of the following examples come from a small region in the center of the image.
In the first image, the standard integration result shows signs of atmospheric dispersion but otherwise the stars look reasonably good.
In the second image, a drizzle integration with scale=1 and dropshrink=0.9, the horizontal anomalies appear.
In both of the above, after integration I ran PhotometricColorCalibration and then ArcsinhStretch.
The following shows a single star, a) RGB immediately after integration with unlinked STF, b) separate red, green and blue channels with STF, and c) RGB after PCC and AsinhStretch. This is also available for download.
The problem in the drizzle integration is particularly evident in the blue channel: in the monochrome blue image note the sawtooth patten. In the stretched color image, note the two very blue rows at the bottom separated by a more neutral row, and a similar pair near the top where there are two bluer rows separated by a redder row.
I did not notice this problem until recently. One thing that changed for me is that I began using a higher resolution one-shot-color camera with dimensions 9576x6388. It occurred to me that this might be some kind of rounding error with coordinates, but if so it seems evident only in the smaller (vertical) dimension and only in the blue channel.
It is challenging to see how this can be operator error but I would be happy to be corrected.
John
All of the following examples come from a small region in the center of the image.
In the first image, the standard integration result shows signs of atmospheric dispersion but otherwise the stars look reasonably good.
In the second image, a drizzle integration with scale=1 and dropshrink=0.9, the horizontal anomalies appear.
In both of the above, after integration I ran PhotometricColorCalibration and then ArcsinhStretch.
The following shows a single star, a) RGB immediately after integration with unlinked STF, b) separate red, green and blue channels with STF, and c) RGB after PCC and AsinhStretch. This is also available for download.
The problem in the drizzle integration is particularly evident in the blue channel: in the monochrome blue image note the sawtooth patten. In the stretched color image, note the two very blue rows at the bottom separated by a more neutral row, and a similar pair near the top where there are two bluer rows separated by a redder row.
I did not notice this problem until recently. One thing that changed for me is that I began using a higher resolution one-shot-color camera with dimensions 9576x6388. It occurred to me that this might be some kind of rounding error with coordinates, but if so it seems evident only in the smaller (vertical) dimension and only in the blue channel.
It is challenging to see how this can be operator error but I would be happy to be corrected.
John
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