1. I thought the script would make the dark-master frame iteself and USE IT internally without having to take double exposures each time. But from other read and the manual of the script you suggest that I should use the RAWTherapee dark-frame option in post-process.
Correct, the dark frame option in the script is only there to allow you to take images with the shutter closed. You should be able to use them in any workflow that supports dark frames, though you may have to convert the format.
If your workflow supports it, making the master dark using median should give better results than the in camera average.
2. Would it be possible to have CHKD or the script itself, to have the option to subtract the MASTER DARK FRAME on the camera.
Raw subtract can technically be done from script, but it would be very slow (you can try the subtract option in the file browser to see), which would defeat the purpose of disabling Canon dark frames in most cases. If you're going to the trouble to make separate dark frames, you're better off doing the processing on your PC.
3. I cannot find the "RAW COMBINE" function mentioned in the scrip manual. Is it supposed to be somewhere in the menu of CHKD?
Raw operations are available in the CHDK menu from the file browser:
https://chdk.wikia.com/wiki/CHDK_User_Manual#File_Browser4. I actually really want to use the Fiji or AstroImageJ programs but I cannot get them to work properly with the DNG files.
Unless there's some problem specifically with CHDK DNG files, that's between you and those programs. You might have better results converting DNG to another format first.
If the programs specifically have trouble with CHDK DNGs, it might be caused by the packed 12 bit format, which is valid but somewhat less well supported than 16 bit. In that case, you could run them through adobe DNG converter.
If the problem is DNG support in general, rather than the fact that they are bayer raw, there are some programs you can use convert to a simple 16 bit format without debayering, for example dcraw, chdkptp, or rawconvert from the chdk source.
5. RawTherapee is extremely slow on my very decent laptop and it crashes also.
If you are using windows, the performance may be improved a lot by closing all the different control areas you aren't using. E.g. a top level group like "exposure" has a triangle next to it, which points down when all the options are open, and to the right with they are closed. Close all the ones you aren't using. There's some weird GTK/windows issues that makes it super slow if the options are expanded. This is true even for tabs which aren't currently visible.
On my system (old sandy bridge i5), this makes the difference between unusable and slightly sluggish.
It represents the raw files very weirdly with messed up colors and values.
By default, raw therepee does a contrast stretch, which is very ugly when a large portion of the image is near black level. Clicking the "reset" in the exposure tab (or "neutral" for older versions) will give you a much more normal rendering. If you make a workflow based on raw therapee, you will want to create presets that you can load as a starting point. If you shoot a bunch of images for a stack or something, you create one profile for batch and "paste" it onto all the other files. It also supports running batches form the command line, though I haven't actually used that.
FWIW, I don't specifically recommend raw therepee as the best tool for the job, I mention it because it's a program I've found good enough for my personal needs.
