Digital BW, The Print

> From: Jeff Medkeff
>
> I understand what raw is, and I pay very close attention to white
> balance when shooting raw - as do a great many photographers. One reason
> is that I rely upon the histogram to insure I am getting the levels I
> want in the photograph. The displayed histogram on every digital camera
> I've ever picked up is a histogram of the demosaiced image, with a white
> balance correction applied. So, if I did not set the correct white
> balance in the camera at the time of shooting, my histogram will be
> systematically in error when displayed in camera. That can lead to
> problems - clipping, if the systematic error reduces levels in a color
> channel of interest; or excessively lowered signal to noise ratio if the
> systematic error increases levels. This, in turn, certainly affects BW
> conversion and the ability to process for printing down the line. This
> is a major technical reason to set the white balance correctly in
> camera, when shooting raw.

But as you note, the histogram describes the image _after_ applying a
particular white balance correction. It doesn't necessarily tell you if your
raw file has any clipping, or excessive headroom, in any channel. If that's
what the histogram shows, then ideally you'd want to select a white balance
that reflects the native white balance of the sensor itself, so that the
histogram would most closely approximate what's coming off the sensor. The
optimum white balance for that purpose would have nothing to do with the
color of the ambient light.

> There is also a reason involving convenience. As already mentioned, it
> is de rigeur to color-meter the light and set this in a digital camera
> directly. Alternately, you can shoot your gray card and set a white
> custom balance by selecting that image in-camera with the appropriate
> menu choices, the camera deriving the color temperature and tint terms
> necessary to balance images in that light. It is a great convenience, if
> you are doing either, to have your conversion software automatically
> respect this setting, rather than having to try to figure out what the
> setting was, or read it off redundant paper notes you took at the site
> and type it into your raw converter manually. Clicking on photos of gray
> cards in the converter works fine, but it is more labor intensive (in
> some converters, significantly more) than just having the converter read
> the raw metadata.

I think it's probably easier just to snap a raw picture of your gray card,
under the same light as your subject, and then use the white balance
eyedropper (or equivalent tool) in your raw converter. That eliminates the
need to do anything WB-related in the camera.

--

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@...