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I always thought that after a 3x Drizzle stack (in DSS) and some work on the image reducing it to a smaller size would give sharper images. I did now a comparison of a very cropped M57 image, and I see the following: https://www.astrobin.com/35txmy/?nc=user As mentioned in the image, I kind of understand the result, but then I ask myself for what the resample tool is good? If I resize in IrfanView I do not see any major differences. Can somebody explain the Resample process in PI and maybe more important, when to use it? I might have screwed up some of my images and did not even realize. |
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Uwe Deutermann: Hi Uwe, I kind of agree with you. I already resampled some of the few drizzle integrations I made and there is clearly a degradation of the resolution. Kind of asked myself the same question, what is the point if you resample and obtain the same aspect as a normal integration? I experimented with drizzle 2x but abandonned afterwards. The key is probably the interpolation process and settings. I cannot be of great help I'm afraid. |
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Open resample. Go to the interpolation menu and try another algorithm. Some algorithms have adjustable parameter so play around to get what you want. It looks like "Auto" isn't working well on your image. |
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Uwe Deutermann: Resample with <100% (reduce size) can be used to: reduce an image after a drizzle stack, reducing the image size for sharing on the web, or to increase SNR of oversampled images at the cost of resolution. Resample with more than 100% (enlarge size) is not used very often, at least by myself, except maybe to upscale 2x2 binned CCD data to match a 1x1 luminance dataset, but the drizzle process is more accurate for upscaling of raw data. Bogdan Borz: If you stack with e.g. 2X drizzle, then resample to 50%, you will obtain the original resolution but with rounder/smoother stars (less aliasing). This only works well if the original data is undersampled, since the drizzle process was written for undersampled Hubble images. |
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| Hi Victor, yeah that was my idea but I didn’t see a difference. As you say you should use it when undersampled, but what would be the threshold ? |
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Thank you all for the information, I think it goes along with that from what I have heard from others as well. A friend passed me this link: https://astronomy.tools/calculators/ccd_suitability which shows when under- or oversampling is happening. So for my setup I really do not need it, I still think that it gives a slightly better image when I drizzle 3x (but that might be just my imagination!). I definitely agree with David that the Resampling is with Auto configuration not working well, I will try some others! And now that I know what can happen I will have an eye on this and will resize with other tools. Or we shall trust the astronomy tools results and just do a 1x drizzle! Again, thank you for the discussion, this is what Astrobin is all about! |
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Hi Uwe, Actually I found in Warren Keller's book "Inside Pixinsight" that Drizzle is indicated when FWHM is under 2 pixels (that makes your stars looks square not round, too few pixels). You can use the FWHMEccentricity script. CS, Bogdan |
