Recommendations for white Color Balance with modified DSLR

[bjaffa]

I am relatively new to Astrophotography and Pixinsight.
I recently had my Canon DSLR 3ti modified for full spectrum. Prior to modifying my DSLR had
processed several images using Pixinsight with the batch preprocessing script.

I am looking for recommendations on how to handle white balance with my newly modified Canon 3ti.
I have read several posts concerning white balance and I am somewhat confused.
Should I try to use the backgroundneutralization and colorcalibration processes or try to use some other
approach to extract the white color balance metadata from the raw image and preprocess the image
prior to batch preprocessing?

Thank you for any help. 
Brent Jaffa
 

[aworonow]

bjaffa,

You are pretty much free to do anything you want. You can white-balance the camera to daylight, for instance, using the custom white balance setting and a gray-card. Then you can shoot daytime and deep sky. Or you can ignore it all and simply adjust the colors in PI. The latter is basically what happens when you shoot RGB with a mono astro-camera. Remember, if you use RGB filters on the BW camera, you do not need to tell PI what the bandwidths of the filters were--and they differ from manufacturer to manufacture. Similarly, with a OSC, PI does not need to know if the camera was modified or not. You simply 'direct' the color calibration as needed.

(Of course, you could debayer the OSC image into separate RGB and pretty much precede as if you shot gray-scale images through 3 separate filters.)

That's my take, any way. See what others thing!

Alex

[aworonow]

forgot to mention...some camera mods allow white-balancing to daylight, others do not. Consult your mod-source's web page.

Alex

[bjaffa]

If I take a white balance image (18% gray card method) and use the DSLR custom white balance option:
How do I apply custom white balance data stored in the DSLR raw format metafile to the raw image for
Pixinsight to process?

Thanks for advice.

Brent

[aworonow]

Brent,
I'm not sure of the answer to your last question.. Could be that RAW is not completely raw. That has been true for previous cameras, at least for earlier Nikons. But, when I do an outdoor white balance calibration, I use it so that I can take scenery shots, but don't usually bother changing settings on the camera when shooting deep-sly. (You would have to recalibrate w/ gray card for incandescent lighting, for instance, but that calibration would also work as a starting point for deep-sky.) One thing you can do if you want to get a good starting RGB balance is to deBayer the DSLR image, then take, say the green image (because it usually has better signal-to-noise due to having 2G pixels for 1-each R & B) and linear fit the R & B to the green and recombine the images using, for instance, the LRGB procedure.

One thing to be aware of is that you should use the batch deBayer script and not operate on the integrated (stacked) images, since stacked images do not retain the camera's Bayer patter.

Another resource for judging and selecting color balance is to see what others have done. I usually brouse AstroBin and DSO Browser just to get an idea of what others have done and how I might like to vary the image color balance or saturations, etc.

Alex

[bjaffa]

Thanks Alex,

It is my understanding from what I have read, that on a Canon (3ti) RAW image (*.CR2) the custom white balance is not
applied to the RAW data but parameters are contained in the metafile data header which reflect what the
custom white balance should be. And that somehow you apply the parameters to the image before processing if
you desire or else use backgroundneutralization/colorcallibration to adjust later on.
So I think the RAW image is completely RAW.

Thanks

Brent