I am capturing raw images using N900 camera. It gives me DNG files. I have some question regarding the colour temperature of these raw images.
I am trying to map the CIE-XY Camera white point values given in this DNG image to its colour temperature value. The DNG tag is :As Shot White XY
Steps in Experiment :
For this I have set the White balance mode on N900 capture application to manual mode. All other settings like Shutter speed/Aperture/Focus are in Auto mode.
Then I set a particular colour temperature using a slider provided by the app.
Capture raw image of a scene(general) indoors.
When I inspect the metadata present in this DNG file, it has two CIE-XY white point values: As shot XY. Say, x1,y1.
Then keeping the colour temperature setting constant, I just capture a different scene, by slightly moving the camera by very small amount.
Now when I see the XY values, they seem to be different(slightly) than earleir image ones. Whereas I thought since camera is in manual WB mode, and colour temperature set is unchanged, it should have given same white point values.
Am I correct in thinking that 'As shot White XY' values present in DNG metadata give the white points at that set colour temperature?
If yes, why does it change in above setup. Does colour temperature depend upon the CMOS sensor temperature or some other parameter like exposure (Aperture/Shutter speed)?
Any pointers regarding WB, Colour temperature, CIE coordinates, XY white points would be useful.