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Last year, I had compared the white balance adjustment capability of Photoshop 7's ACR plug-in to Nikon Capture 3.5. I came to the conclusion that there was no difference. A recent discussion on the DPReview Nikon forum raised the question of where white balance is applied. The result of that discussion was that no, white balance setting does not have an effect on the Raw file. White balance, as it turns out, is applied after a RAW file has been recorded, by the converting software.* The above conclusion is in agreement with my tests of last October, however I feel it is necessary to repeat them with PSCS's ACR v2.3, the current version (version 2.4 is in beta as of this writing.) To demonstrate that white balance is applied after the image is saved, I took a series of photographs of a still life, under incandescent illumination consisting of two lamps in reflectors, using 100 watt Reveal™ bulbs, at various white balance settings:
These photographs were taken with a D100 on a tripod and a 24-120vr lens set to 1/60th of a second at f/8. The white balance settings are as follows:
A 'best' white balance was determined to be 2850K, -12 tint by measuring the average color inside the blue squares, and adjusting until the color are neutral:
Each of the exposures in the matrix above were then adjusted to this white balance:
The top left (incandescent +3) and bottom right (shade -3) white balances are the most extreme, representing 2500K and 7650K respectivly. These two, converted exposures were then examined in detail. In the first area, the orange thread, light cream color of the glue, and white background were examined. In some cases, the red channel seems to have been 'blown', so this tests the accuracy of the white balance conversion in those areas. Again, the blue squares represents areas where the color was sampled:
Incandescent +3 conversion:
Shade -3 conversion:
Next, various well saturated colors were similarly tested:
Incandescent +3 conversion:
Shade -3 conversion:
The images were made at ISO 400, so some digital noise would be visible. There is no apparent change in the noise characteristic between white balance settings either. There is no difference between a photograph which has had the white balance set correctly in camera, and one which has had it adjusted in Photoshop's Camera Raw plug-in. Presumably other Raw converters also convert white balance in this way. Therefore, it is concluded that the white balance is added to the image after the file is saved. The white balance is also saved, as a setting. * The image displayed on the LCD of most DSLR cameras is a JPEG image, and the white balance setting of the camera is applied to that image. It is also applied to the histogram that is shown as well, so from the stndpoint of reading the exposure from the histogram, setting the correct white balance on the camera will be an advantage.
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