HDR Composition Challenge

[greg.dulaney]

I've captured 300 sec, 60 sec and 15 sec images of M42, using a RASA8 with a QHY12 (OSC).  The images were calibrated with darks of matching duration, flats and bias frames.  The 300, 60 and 15 were preprocessed with batch preprocessing and then DBE.

I registered the 3 master lights from BPP with Star Align.  Then used the registered images in HDR Composition with default setting, in the hopes of restoring the blown out trapezium.  Not only is the core of M42 still blown out the fainter details have a "cartoonish" artifact.  I did vary the defaults without any meaningful affect.

Any suggestions on how to accomplish the HDR image of M42?  Interestingly to me the gradients in the shorter exposures are worse than the 5 minute image.

Screen shots of my preprocessed images and the HDR composite are attached.

Thanks for you help!
Greg Dulaney

[greg.dulaney]

So HDR Multiscale Transform after HDR Composition seems to have done the trick.

[Juan Conejero]

Hi Greg,

The "cartoonish" appearance you have noticed is perfectly normal for HDR images. Technically this is called posterization, and happens because the image cannot be represented with the default 16-bit transformation used to represent linear images on the screen. You should enable 24-bit STFs for images generated by the HDRComposition tool.

If you want to learn more about HDR images, posterization in screen representations, and the 24-bit STF feature, here is an article I wrote years ago:

https://pixinsight.com/tutorials/24-bit-stf/

Once you have an HDR image, you normally have to compress the dynamic range in order to make visible hidden structures. This is the purpose of HDRMultiscaleTransform. You have a good example at the end of this processing example:

https://pixinsight.com/examples/M81M82/index.html#Dynamic_Range_Compression

[greg.dulaney]

Thanks for the help!