Color Balancing Advice

[smashing]

So just got around to playing with the M31 data I collected a while ago, it's just over an hours worth of integration under very bright moonlight.

Something I really seem to struggle with is my Color balance, I have a modded camera so everything is slightly red anyway but when following the tutorials for M31 the end results are all quite blue whereas mine comes out kind of...muddy. So my process for the picture here was

• Stack in DSS
• Open up in photoshop and convert to 16bit
• Threshold layer to identify dark spot and put an info reference down, white reference was the galactic core (other photos I have tried to find a star like our sun but couldn't find it this time and the tutorial did this)
• Open up levels and move individual channels to match info reference 1 (black point)
• White point never seems to need moving at all (does that sound right)
• Use adjustment layers to adjust curves etc etc
• Action tools/star reductions etc etc with some tweaks to get the final image

So a few questions

1. The white point side of things bothers me as it I think i'm missing something so any pointers there would be great.
2. From a black point perspective as I use curves to stretch the image the initial numbers (say 20) increase...stupid question when I level them back out again do I keep aiming for 20 or do I go as far as I can before I start clipping the histogram and then balance them there?
3. When I first open the image is there a way to align all the channels? 

Any help would be great, I have also attached the base TIF if anyone wants a go at the data.

Autosave021.tif

[vlaiv]

Thing is that most people boost color too much in images.

Your image is actually properly color balanced. I measured on a 0.48 color index star (that should be closes to white) and it matches.

If camera is modded this means that color transform matrix will be a bit off and you'll get stranger colors. Ideally you want to do your color correction manually (shooting color charts and then deriving color transform matrix).

Most of the times you'll see M31 processed something like this:

But in reality, true color of that galaxy is more like this:

Your camera does have a color cast due to modding that needs to be addressed, but I believe second one is very close to true color of the galaxy.

Just as a reference, look at these two images:

and this:

First is Hubble team rendition of part of M31, and second is color for different spectral types under D65 illuminant equivalent (sRGB used on internet uses D65 white point). As you see, last two images match almost perfectly, but you rarely find M31 that is rendered like that. Your image is close but there is a "brownish" cast probably due to modding.

[smashing]

32 minutes ago, vlaiv said:

Thing is that most people boost color too much in images.

Your image is actually properly color balanced. I measured on a 0.48 color index star (that should be closes to white) and it matches.

If camera is modded this means that color transform matrix will be a bit off and you'll get stranger colors. Ideally you want to do your color correction manually (shooting color charts and then deriving color transform matrix).

Most of the times you'll see M31 processed something like this:

But in reality, true color of that galaxy is more like this:

Your camera does have a color cast due to modding that needs to be addressed, but I believe second one is very close to true color of the galaxy.

Just as a reference, look at these two images:

and this:

First is Hubble team rendition of part of M31, and second is color for different spectral types under D65 illuminant equivalent (sRGB used on internet uses D65 white point). As you see, last two images match almost perfectly, but you rarely find M31 that is rendered like that. Your image is close but there is a "brownish" cast probably due to modding.

Thank you for taking the time to respond to this! I shall look into the colour matrix stuff and see if I can get my head wrapped around that.

[vlaiv]

20 minutes ago, smashing said:

Thank you for taking the time to respond to this! I shall look into the colour matrix stuff and see if I can get my head wrapped around that.

It is really not hard, but there is no specific software to do it simply.

Most DSLR cameras have inbuilt color correction profiles (WB presets) and you could probably find those online for your camera, but they will be for unmodded version.

For modded version, you need to calculate it yourself by shooting color charts / passports and then measuring things.

Here is an example I did. I took color passport image and put it on my phone (phone is not color calibrated and in order for this to work it really should be, but I did it more as an exercise):

This is original image I put on my phone:

And here is what raw linear data looks like:

Not properly color balanced (white is not white) and not color corrected.

After white balancing and gamma 2.2 being applied it looks more like regular color (but not quite, red is not saturated enough and colors in general look "washed out"):

Finally, after applying color correction matrix, this is resulting image:

(and color template next to it for comparison). There are still some differences - red is now too saturated and teal is not quite good, but overall this is the best result and colors are the closest to original template.