Adjust White balance?

Question

I'm looking at some image processing algorithms for white balance manipulations. Seems like a previous Stackoverflow [question](https://stackoverflow.com/questions/1175393/white-balance-algorithm) answers the question of automatic white balance algorithms rather well. However I'm wondering how to convert from one temperature to another, i.e. Making the assumption (and its a big assumption) that a white balance algorithm could take a processed image (e.g. JPEG etc) and place the overall temperature in a scene at 6500, how would you algorithmically "cool" or "warm" the scene to a specific temperature? This would be a common operation in an image editing program, albeit these typically operate on RAW images which have no processing applied (colour space manipulation or otherwise)- In the case of RAW files - perhaps the individual RAW files contain sufficient information (in the file header) regarding the colour calibration of the camera sensor to make the specific temperature transformation more deterministic? Any input appreciated - thanks!

Answer 1

...how would you algorithmically "cool" or "warm" the scene to a specific temperature?

I'm not sure about doing this algorithmically per se, but here are a couple specific methods:

1. In Lightroom, in develop module, use the white balance selector, by the temp and tint sliders. Click on the eyedropper icon, and then click on a part of the photo that you want to be neutral, such as a gray card, or gray wall, sidewalk, white wall that's not too bright, etc.
2. Just move the temp slider back and forth, and note the 4 digit number on the right, those are degrees Kelvin.
3. With a photo open in Photoshop, you can go to Filters: Camera Raw Filter (even if image is not raw), and do either of the above methods (white balance eye-dropper is in the upper-left of Camera Raw window; temp slider on the right).

Does that answer your question? I'm not sure what you're getting at regarding algorithms; feel free to follow up with more questions.