Everyone knows how to process their DLSR images don't they?
Using traditional techniques you calibrate your raws with darks, flats and bias frames. You demosaic them into colour then stack them. You then apply your white balance and then some kind of data stretching such as Photoshop curves. Great, you've finished! Or have you?
If I apply the same sequence to a normal terrestrial image this is an example of what I get:
However the JPG that came straight out of the camera looks like this, which is a far more lifelike result:
If I process the RAW using Photoshop (with Adobe Camera Raw) then I get something almost identical to the in-camera JPG.
So why has the usual astro-processing sequence left a dull lifeless result?
The answer is a missing matrix!
Such a matrix can be often be found at DXOMark - e.g. for the Canon 600D: http://www.dxomark.c...s#measuretabs-7
So for the 600D the colour matrix is:
2.12 -1.28 0.16
-0.24 1.63 -0.38
0.04 -0.69 1.65
This must be applied to the white balanced data to transform the image into something that will display correctly on your display device.
Applying this matrix to the above lifeless image gives me this:
If you're not familiar with matrix maths then it works like this. If a pixel in your white balanced image has values r,g,b then they must be transformed to RGB as follows:
R = 1.879574 * r - 1.03263 * g + 0.153055 * b
G = -0.21962 * r + 1.715146 * g - 0.49553 * b
B = 0.006956 * r - 0.51487 * g + 1.507914 * b
Those numbers are for the Canon 600D, so you need to substitute the numbers given for your own camera. Also, this transformation should be done before you apply your stretch. I manually applied a 1.6 gamma stretch to the images above. The ACR stretch is slightly different.
ACR is applying a very similar matrix automatically when it converts the image from a raw file.
The only problem I've hit so far is that this matrix transformation doesn't seem to work well for H-alpha modified cameras - the red becomes too overpowering.
Edited by sharkmelley, 02 March 2016 - 03:26 PM.