I recently posted this on the diffraction limited support forum bit I imagine a lot of Observers use the same software. Let me know your thoughts! Greatly appreciated.
Hello, I'm new to DSLR photometry. I've had Maxim DL 6.14 for sometime but just recently started to dive into it's scientific applications. I use a Canon Rebel T6i now for AP and want to begin using it to collect science frames. (Although soon upgrading to a full frame 6D, hopefully). I understand calibration but what I'm not certain of is how to extract the Green 1 and Green 2 channels and then average them together to perform photometric analysis on the averaged Green image which then corresponds to the standard V filter. I've come across bayer extraction in Maxim DL but the instructions are somewhat vague. If anyone could provide further clarification it would be greatly appreciated! I've included some text from the AAVSO DSLR photometry Manual below:
"Traditionally in DSLR photometry only the Green channels are used to estimate Johnson V band magnitudes. However, this ignores information contained in the Red and Blue channels which, in many situations, can be used to accurately measure stellar magnitudes in Johnson B and Cousins R bands, respectively...We want to separate the R, G and B color channels from the original RAW greyscale image, a process called color separation. The resulting images are also greyscale. Many photometry programs are able to extract individual color channels from RAW images, although the procedure may be different for each program. For example, AIP4Win extracts both green channels and present them as a unified image of the same size as the initial image. Conversely, MaxIm DL extracts each green channel separately. The best procedure is to extract both green channels, average them together, and perform photometry on the resulting image... Color separation may be performed before or after image calibration. It does not matter which order you choose so long as all data (calibration frames and science frames) are treated identically.
While I'm asking, based on the final statement above, do calibration frames need to be color separated as well? thanks in advance! Zak
And welcome to DSLR photometry!
Attached is a Maxim script that can help with speeding up the de-bayering process. Save and rename as a .vbs file on your system. Load a couple DSLR images into Maxim and then execute the script, either from the Maxim menu or just by double clicking the script. The images in Maxim will be debayered, ready to be saved. Study the script: its pretty easy to understand and modify. Happy to help if you have questions.
As for the calibration: calibrate the full frame and then debayer the result should do the trick.
Once you get rolling you can look into transforming your TB, TG, TR images into standard B,V,R colors. You can submit either to webobs, but the standards are prefered.
Always more things to learn!
Thanks for the warm welcome! The script ran beautifully with no problems. For my next question, I see that it splits the image into R, G1, G2, G and B color channels. Do I stack and average the G1 and G2 only? I'm just not sure what to do with the G image. I'd definitely prefer to transform into standard B, V, R colors so thats next on the agenda for learning. I really appreciate the help. Zak
Ah, you should read the script! It is code, but pretty understandable with the Maxim help file near to hand. The script offers the individual G layers(G1 and G2) as well as their sum (G); pick which you want. SInce you're learning how to work with Maxim, exercise its tools: try adding G1 to G2 and then compare it to G; they should be identical. Trust, but verify! For instance: the script has assumptions about the bayer layer layout. Is G1 very similar to G2? Should be. If not your camera has a different bayer layout.
To make the transformation to the std BVR system you will need to do some imaging of stdfields and the analyse the data with TG, Gordon's TransformGenerator program.
Lot's of steps. Have fun!
Awesome! Thank you again. I took another look at it once I got in from work ... now I see the combine G portion of the script. I'm excited get started. Really appreciate it. Zak
Beleive it or not but I'am in the same place you are or was. I was going to ask the same question on line, but I ran across you question and Mr. Greeting Zak answer. I to have a Nikon 7000 DSLR camera and I'm in that same situation. I do have Maxim DL Pro and filming through a 8" Astrograph Telescope. I took 12 images of Beta Lyr ,16 Bias, 16 Dark Frames and 16 Flat Frames. I know Maxim Dl somewhat because I did the Pictures of some Nebulas, star clusters and some galaxies. Now that I,m into the scientific part of varriable starts. I'm at a tee because I dont know how to extract the green channel in Maxim DL Pro to do Photometry.. Can you guide through the process on how to extract the green channel please.