On Feb 25, 2006, at 1:56 PM, Mark Roberts wrote:
What you're asking is not possible. Once a file has been saved in
another form, like TIFF, JPEG, PSD, it cannot be reconverted back
to RAW.
Just for my own curiosity, is it because of nature of the file itself
(as in, is it theoretically impossible) or is it just a software
limitation?
Well, sort of both...
In a RAW file, each pixel is either red OR green OR blue, in 12-bit
values. Once the file is demosaiced into a 24-bit or 48-bit bitmapped
image in which each pixel contains red, green and blue data, it's a
big
job to convert it back. Probably could be done but I don't know if
anyone's done it yet.
As I mentioned before, DXO Labs software *can* manipulate "lighting",
which I take to mean brightness/contrast/highlight/shadows, and
save in
RAW format.
If so, that's the first I've heard of it. It would be a neat trick,
but how useful I don't know.
To do it would require holding on to both the original RAW sensor
data and the output RGB channel data, evaluating the differences on a
pixel by pixel basis, doing whatever adjustment is required, and then
interpolating back the appropriate sensor data value in the original
matrix. You can't invert the functions to get an analytically correct
number, but you can get arbitrarily close in approximation.
Godfrey
