Tutorial:
DSLR cameras RGB multipliers

Content:

1. Introduction
2. Download DCRaw and copy to a folder
3. Open Command Window
4. Change directory in Command Window
5. DCRaw parameters
6. Get cameras RGB multipliers or white balance values

6: Get cameras RGB multipliers or white balance values

Now we are ready to get information from the raw file.

Type dcraw -v -w filename. In this case: "dcraw -v -w img_7137.cr2".

We can now see that Canon 6D has the multipliers:

• Red channel: x1.961914
• Green channel: x1.0
• Blue channel: x1.632813

This is the gain factor for the red and blue color channels relative the green channel. Multiply the values with this and then you get what Canon thinks is a natural color for a daylight scene. You can set the gain factors in your astro image editing program, like DSS (Deep Sky Stacker), Fitswork or others program you use. Most of them shall have a multiply function, or you can set the values already when it read the raw files. I do prefer to do it later to have more control of it. This is a rough estimation, but you come much closer and make it easier to get a natural look.

Note:
You must at least bias calibrate your image if you apply this scaling after that you have the raw files read in. After the scaling has been done the first look will normally be a very red image, that's because of light pollution. You shall now subtract (not multiply) away the background (light pollution).