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Why does Drizzle affect color?

Edward Lubat
in PixInsight
Hi Adam,

Using an OSC (ZWO ASI071) I am finding that employing Drizzle, by itself, creates a profound green cast, not sure why.  I am currently working on an image of NGC 4565 I recently acquired.  Here is what the image looks like after complete preproscessing (calibration/integration) without any further processing, without drizzle (automatic STF applied):

This is what it looks like with everything done the same way, but using Drizzle:

(Note that I used both Auto and RGGB for the Enable CFA Drizzle setting, with no difference).

This is what the non-drizzle version looks like after Background Modelization, Deconvolution, Background Neutralization, Photometric Color Calibration, and a dose of SCNR (again, with auto STF applied):

And here is the Drizzle image after identical processing:

Am I doing something wrong?

Thanks

Ed

Comments

  • BlockHeadBlockHead
    I will try to take a look perhaps this weekend (if someone else does not first). 
    I have not seen that effect with a regular CCD (mono/filters). 

    I do wonder why people do not extract the pixels directly and avoid any interpolation.. that is often the cause of issues with OSC. Anyway, wild speculation.... 

    -the Blockhead

  • Edward Lubat
    Thanks.  Just so you don't end up on a wild goose chase, I have  continued processing this image (not quite done yet), and when I got to delinearization, instead of using the automatic STF as a starting point (which I usually do but avoided here because of the color cast), I did my initial stretching manually using Histogram Transformation and then Arc Sin Stretch starting directly with the linear image, and colors are totally fine.  So there doesn't seem to be anything that intrinsically wrong with drizzle messing up the colors, but something about this particular image after using Drizzle is make the STF "guess" wrong about what a good stretch would be (at least that's what seems to me is going think).

    Ed
  • BlockHeadBlockHead
    Ok... I am going to let this one go unless you come back and say there is a strong case of something at play.
    -the Blockhead
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