Finally, a D300 Near UniWB JPEG

Started Apr 3, 2008 | Discussions thread
auhopu New Member • Posts: 16
Re: RAW uniwb for D300

Hi Guillermo,

I suspect we do something differently or maybe you "think Canon" at some point
I will try to explain.

There are two ways to set a custom WB setting on D300.

measurement method:

by taking a direct measurement off a white or gray (or magenta in our case) object that fills the whole viewfinder and store it as "d-0" preset. this setting can then be copied to any preset from "d-1" to "d-4" so it won't be accidentally erased by a new measurement. (note that there is NO picture taken in this process!)

file method:

by copying WB from an existing file to one of "d-1" to "d-4" presets. the file does not have to be an image of a white or gray object.

(see page 136 of D300 manual for further details
http://www.nikonusa.com/pdf/manuals/noprint/D300_en_noprint.pdf )

Your comment

"those are the coefficients embedded in the RAW files, not the coefficients one gets when using that RAW file to adjust WB"

raised an important question.

Which of the following happens when D300 adjusts WB based on an file?

a. It sets WB by averaging the whole image, like the "-a" flag in dcraw
(is this what you implied?)
b. It sets WB by using the file coefficients

Before your last post, I believed it did "b." , so I made an experiment to verify.

I shot
DSC0055.NEF with WB set to "d-1" (original magenta measurment) DSC0056.NEF with WB set to "d-2" (WB based on the raw image I sent you)
DSC0057.NEF with WB set to "d-3" (WB based on DSC0056.NEF)

I then developed with "dcraw -w" and saw that the camera recorded the same multipliers in all images... which means "b."

C:\data\D300\UniWB\myuniWB> dcraw -v -w -T -4 DSC0055.NEF
Loading NIKON D300 image from
DSC0055.NEF ...
Scaling with darkness 0, saturation 16383, and
multipliers 1.000000 1.036437 1.004049 1.036437
AHD interpolation...
Converting to sRGB colorspace...
Writing data to DSC0055.tiff ...

C:\data\D300\UniWB\myuniWB> dcraw -v -w -T -4 DSC0056.NEF
Loading NIKON D300 image from
DSC0056.NEF ...
Scaling with darkness 0, saturation 16383, and
multipliers 1.000000 1.036437 1.004049 1.036437
AHD interpolation...
Converting to sRGB colorspace...
Writing data to DSC0056.tiff ...

C:\data\D300\UniWB\myuniWB> dcraw -v -w -T -4 DSC0057.NEF
Loading NIKON D300 image from
DSC0057.NEF ...
Scaling with darkness 0, saturation 16383, and
multipliers 1.000000 1.036437 1.004049 1.036437
AHD interpolation...
Converting to sRGB colorspace...
Writing data to DSC0057.tiff ...

So once a WB measurement has been taken, all images based on this WB setting inherit the same coefficients. If any of these images is used to set WB for further shooting, the new images inherit the same coefficients as well.

What I do not understand is: how did you end up to an image with coefficients different from 1.000000 1.036437 1.004049 1.036437 by setting WB based on an file with these?

Best regards,
Elias
--
http://www.auhopu.com

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