APT - Pixel Aid to get ADU values from RAW files

[BrendanC]

Hi all,

Title says it all!

I'd really like to start analysing my images more as they come through from my EOS1000D, particularly ADU values.

However, the Pixel Aid tool in APT only reports pixel values for a raw (CR2) image, in bitmap mode, and only for the selected area. Wherever I point it, the max is being given as 250-255, and whereas that does imply to me that my pixels are saturated, this isn't what I'd expect for an ADU value.

The alternative is to use FITS files, but when I try to import one created in DSS, it just doesn't appear in the list of images, so I can't take that route. This should also be able to tell me the value for the entire image or for individual pixels, but even if it did work, it's not ideal because I'd like to see the images direct from having been taken, in CR2 format, not converted into FITS.

Is there any workaround to this? Or is there a better way to interpret the bitmap mode values and convert them to real ADUs?

Thanks
Brendan

[BrendanC]

Wow, I must be getting good. I'm asking questions nobody has answers to now!

[SamK]

Hi Brendan

If you want to get back to basics, Dave Coffin's dcraw has options to get the underlying ADU values from a RAW image:

Using windows command line (with dcraw.exe in C:\temp\dcraw), eg

 dcraw -D -4 -T "C:\temp\dcraw\file.CR2"

The options are:
-D        Document mode without scaling (totally raw)
-4        Linear 16-bit, same as "-6 -W -g 1 1"
-T        Write TIFF instead of PPM

The resulting 16bit tiff produced should will have a maximum ADU value on saturated stars based on the number of bits of your camera, so around 16,000 for a 14bit 450D, 4,000 for a 12bit 1000D. You'll also see the bayer matrix pattern if you open the tiff.

There's a windows build of dcraw.exe here:

https://github.com/ncruces/dcraw/releases/tag/v9.28.2-win

Sam