Superbias: Add support to custom Master Offset/Bias

[deepskystacker]

Superbias: Add support to custom Master Offset/Bias

[perdrix52]

Hi Paulo, FWIW that looks more like a negative flat than a a bias frame to me as it has vignetting (brighter in the corners than the middle). As Bias (Offset) frames are always taken with the lens cap on there's no way they can be vignetted.

If you read C++ take a look at https://github.com/deepskystacker/DSS/blob/master/DeepSkyStacker/TIFFUtil.h (and to a lesser extent) https://github.com/deepskystacker/DSS/blob/master/DeepSkyStacker/TIFFUtil.cpp. You'll see that DSS uses a set of TIFF tags starting a 50000 (decimal) and what each tag means.

[pauloup]

Hi David, thank you for answering!

I know this Master Bias looks very unusual with the inverse vignette, but I assure you I took the bias frames with the lens completely blocked. To shoot the frames, I taped the lens with 4 layers of black electrical tape and put the smartphone in a closed box, and shoot at 1/8000s.

It's a photo from my smartphone (OnePlus 5T), so maybe this is a property of such a small sensor (just 4.61mm wide for 16MP). Or maybe it's some kind of vignette compensation filter built in the sensor or in the camera firmware on Android, or yet in the native Camera app which saves the DNG file. Anyway, unfortunately there's no way I could shot RAW without this vignette signal.

Here's a folder with the edited Superbias, the original Master Bias and one of the original DNGs from my phone for further inspection: https://drive.google.com/open?id=1A6sLgXvuaj_gBHx8D4r5djajRszGVrPW

Thank you for pointing the source code of the TIF custom tags. Until now I just couldn't find a way to edit my TIF to include these tags. I even tried a Hex editor, but dealing with all byte offsets was making me crazy. Exiftool can't handle TIF custom tags by default, but thanks to your support, I was able to find a way to add custom tags with Exiftool. Now I'm excited to test my edit and see if it improves the stacking result somehow.

Again, thank you so much. I'm gonna write a later comment here with instructions to help others who may face the same issue.