Flash Light Temperature

[tomczak]

PWP RAW uses 5500K as a flash colour temperature. One Canon camera seems to be using 5350K, while another ~6800K if WB is set manually to flash. How come? Do electronic flashes differ that much in colour, or does Canon crank it up on purpose to make the images look warmer?

[tomczak]

That was 6350K and ~6800K for Canon cameras, not 5350K.

[ksinkel]

The color temperature values in the raw dialog are common values for the situations listed intended to be used as starting values. There is no guarantee that tungsten light, for instance, will be 3000k, that's just a good first guess. It could vary from perhaps 2700k (or lower if a dimmer is used) to perhaps 5000k for a photo flood bulb. Flash and all the other sources vary in their color temperatures as well.

If you know the temperature of the light you are using, you can set it directly on the color temperature slider.

Kiril

[tomczak]

Thanks Kiril, I guess my question is: are the relatively high flash colour temperatures hard-coded in Canon WB for it's in-camera flash units, realistic - is it possible that they describe the average actual light colour or did Canon cranked them up to make the images look warmer? I have no way of measuring it. Cheers.

[ksinkel]

I don't have any specific information on the Canon speedlights -- perhaps you can find information on the particular models on dpreview or the Canon web site. My guess would be that those are the temperatures of the lights involved.

In general I have found that camera wb is rather accurate for the cameras that I use, so I would recommend that setting, certainly as a starting point.

Kiril

[jsachs]

Higher color temperatures and cooler, not warmer. Flash units vary from about 5500 K to 6500 K, probably depending on the power of the flash (Based on physics, I would expect higher power flash to be more blue, i.e. higher temperature).

[tomczak]

What I meant re. the temperatures was that if a lamp had an actual colour temperature of say 5500K, but the preset WB in camera/raw for flash was higher (e.g. 6800), the resultant image will be warmer. Right?

Since it is a small built-in flash unit, I thought that it was done on purpose to skew the white blance since people may have a preference for 'warmth'... I'll check it and report (I plan on shooting the Macbeth with a flash as the only source, with different appreture to see if the flash power makes any difference, white-balance by probing gray pathes in PWP RAW and see what the neutral Temp is - if it makes sense...)

[jsachs]

Right.

[tomczak]

I shot a Macbeth chart in total darkness, using flash only. When setting white balance in PWP RAW using the white balance probe on the gray patches, I can get temperatures between 5500K and 6800K, pretty much randomly depending on a click, even within the same patch (and even more heterogeneous if clicking on on different gray patches). Why is that?

[jsachs]

My guess is chroma noise caused by a combination of demosaicing and sensor noise - If you do the test on a blurred image I suspect you will see a lot less local variation.