Astroart Forum

Hi all,

I'm writing the first post in this forum for asking some basic question on debayering.

I have a raw image from a Canon 450D. The shot is not astronomical but a test image of a red sheet of paper. I also converted the image into FIT format. If I open the raw image with "DCRAW Color synthesis on load" I get the expected image (red, obviously) and the color histograms are as expected (the red histogram is shifted to higher ADU than Blue ad Green).
If I don't select the option "DCRAW Color synthesis on load" the image is opened in B&W. Now using the "CCD Color Synthesis" (with the right Offset and not selecting any other option in the related window) I get a white image and the histogram of R,G and B are centered in the same ADU. It seems that AA is "rescaling" the three color regardless the original color content to have a "white balanced" image, but I didn't asked for that balancing. Is that the expected behavior? Is it possible to avoid that rescaling and get the "just debayered" histograms? If no, could it be and option in the next version of AA? With present behaviour I don't see how to use color calibration coefficient from previous G2V calibration and for the color atmospheric extinction coefficients. I also used the converted FIT image getting the same results.

Further question: Which is the debayering algorithm used for

1) CCD color synthesys
2) DCRAW Color synthesis on load
3) DCRAW Color synthesis on load with High Quality Interpolation

Max

White balance in Astroart Debayering is calibrated to obtain a neutral background, but you are correct that there should be an option to disable it. That will be added in Service Pack 1 available in 2-3 weeks. It will be also possible to set custom R,G,B coefficients.
DCRAW high quality is VNG interpolation. Standard quality and Astroart are linear.

I am using a canon 600d and cannot get the software to debayer a realistic rendition. I have no idea what settings to use for the ratio of red, green, blue to get an accurate image and there is no information available in the manual or online. The dcraw works well, why can the ccd colour synthesis not be automated or at the very least default to the correct values by putting in the camera model.

Which X/Y offset are you using? This is the most important parameter.

r/g/b are not so important, since you will need to tune the color with the command Color Balance, looking at the three histograms. After a correct synthesis (with the correct X/Y), and Color Balance, it's usually required to increased the Saturation to 60-70%. (All this to the final image, the result of Preprocessing). Feel free to send a CR2 or FITS by email for a tutorial.
In Preprocessing, remember to enable the option Color Synthesis, because RAW images cannot be directly aligned (because the shift would destroy the Bayer matrix).

Thank you for your reply. I should start by saying that I am reviewing Astro Art for two reasons, one for a local Facebook group for astrophotography and the other for a dslr astrophotography manual I am writing. I would like to provide a basic workflow for DSLR and CCD calibration and stacking. In answer to your question I am have tried all offset permutations and find that 0,1 works the best. Yes I am debayering before stacking. However, the issue is more fundamental. I cannot get a single CR2 file to debayer correctly. I have tried the Orion Nebula and a normal daytime raw image.
In DSS, Nebulosity and Pixinsight I do not have to enter offsets or RGB value. In fact in your DCRAW it is not necessary. The conversion with DCRAW is good, it looks very like the JPEG image recorded at the same time. I would expect having selected the offset (here you should offer guidance to the user if you do not want to automate this) the RGB values should not be necessary with a DSLR file. The obvious is 1,1,1 but it does not work.
I have tried adjusting the RGB values but cannot get an acceptable conversion, and with a DSLR raw file this should not really be necessary. I can send you a CR2 file from my Canon 600D and 60DA if you like. Any help you can offer would be appreciated because I think Astro Art is otherwise exceptionally good. I think in your software you should have separate options for mono CCD colour synthesis and DSLR/CCD debayering, they are really two different procedures.

I suggest to keep the default values: 0.87 1.00 1.39, with White balance = ON and AntiAlias 40%, adjust visualization = ON.
The commands Saturation and Color Balance are very important after the synthesis.
The Canon 600D X/Y should be 0/1
With Color Balance the first regolation is to move the sliders so that the black point and white point of each histogram is matched.
Yes, send me a CR2.