RAW vs White balance

Started Nov 20, 2006 | Discussions thread
GordonBGood Veteran Member • Posts: 6,308
Re: RAW vs White balance

Ed, it is addictive, isn't it?

I don't exactly see your conclusions in your results as what you have tone responses for a series of white wall images for raw outputs, going by your vertical scale of about a 12 bit range and I'm not sure what the horizontal scale means - perhaps exposure. Clearly, you were clipping at the upper end of the scale so we need to disregard those readings.

I see a definite difference at say the horizontal axis tick between 13 and 14, where the red channel reads something over 3000 in the top chart and about 2500 in the bottom one. That's gain adjustment.

Since I'm patching the histogram program for Jonas, maybe I should patch it for you, too. If I do, I think you are going to see the "typical" Pentax resonse to WB at extreme pre-set settings.

If this keeps up, maybe I should just patch the program to do this for uncompressed DNG and then it can be used by everybody just by converting their raws to DNG using the Adobe utility.

Regards, GordonBGood

edhannon wrote:

The idea that WB may effect RAW files caught my attention. It
would be great if I could reduce red channel saturation in tungsten
light by changing white balance.

So I wanted to see it myself. Unfortunately I have a *istD and the
histogram Java program is for those models that compact the Raw
file by using the top 4 bits of the 16 bit word.

It had been a long time since I have been able to play with writing
software, so I started a background project to implement the
histogram routine in MS Excel QBA. This way I would have more
flexibilty in analyzing the results.

It is hard to stop once you get going on a project like this ... so
now I have an Excel spreadsheet that has QBA modules that will not
onlly draw historams for the *istD but also create tone curves from
a series of "white wall" images. I plot the mode of the values in
the file. This is the most common value.

I did a white wall test early this morning before the sun came up
so I could use pure tungsten light. The results are below.

The first curve is from images shot with white balance set to
daylight and the second with white balance set to tungsten.

The differences between the curves is very small. What difference
there is I atribute to changing light conditions -- the sun was
coming out.

Clearly changing white balance will not reduce Red saturaton in
tungsten light.

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