Digital BW, The Print

Paul D. DeRocco wrote:


> 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 the raw file is clipped, the demosaiced image will clip; but you can 
still clip when demosaicing even when the sensor data is not. I don't 
use mosaiced images, so this is important. And I don't always want to 
apply a factor to the linear data to create my "headroom" for each of 
dozens of images, either.

Your point about using the native white balance of the sensor is fine in 
theory and works great for broad spectrum lighting, for those who have 
figured out what the spectral response of their sensors is (it isn't 
always what Canon and Nikon have specified it to be). But the technique 
can break down when using light sources with emission lines, due to a 
lack of full cutoff in the mosaic filters.


> 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.

You are at liberty to think and do whatever you want, of course; but I 
find it a great deal simpler to set the white balance in camera than to 
go clicking around in raw converters. I use three converters, depending 
on the application. In one of them, I have to open, and click on, the 
gray card photo once for *each* raw file I was converting. That simply 
isn't convenient. The other two converters use different methods to 
apply one click to all subsequent images being converted - methods 
different from the converter already described, and different from each 
other.

Meanwhile, my *cameras* (two manufacturers) use only *one* method of 
setting the white balance. It is much easier to learn how to do 
something one way than to learn three different ways of doing it and 
remember which way goes with which tool.

Of course, with Nikon I guess there is no real problem along these 
lines, because in the US you only get *one* choice of software for 
converting their raw files, unless you want to violate federal copyright 
law.... But my point is that gray-card shooting and ignoring white 
balance at exposure time is *not* consistent with many photographers' 
work requirements.

-- 
Jeff Medkeff
Eagle River, Alaska