Re: Which free software could acquire 48 bits color depth pictures from a scanner ?


On Tue, 18 Nov 2008 06:52:10 -0500, "J. Clarke"
<jclarke.usenet@xxxxxxx> wrote:

Ray Fischer wrote:
Steve <steve@xxxxxxxxxxx> wrote:
To someone who's worried about doing math on
those bits, you MUST know what those bit represent. So just saying
that if "there's a 32 bit channel then the math is 32 bits" is
meaningless without defining what those 32 bits represent.

LOL! You're stuck on the data representation and completely
ignoring
the algorithm.

Uh, this is a photography newsgroup. 32 bits that represent 8 bits of
red, 8 bits of blue, 8 bits of green, and 8 bits of black is a bit
different than 32 bits that represent 32 bits of luminance. You
really do need to know what each of those 32 bits represents before
you start doing calculations on them, at least if the purpose of the
calculations is to support image editing you do. If you're talking
about an encryption algorithm or lossless compression then the data
representation doesn't much matter except to the extent that you might
be able to exploit the structure.

Not exactly. Before you can code an algoritm, you have to know what
the format of the data is. Just saying it's "32 bits" isn't enough.
Because you have to write different code depending whether that 32 bit
data is signed integer, unsigned integer, floating point, etc. The
only people who can say it's just 32 bit data and not worry about what
the data represents are people who are only concerned with the size
and not with doing any math operations on it. Our software hack
friend Mr Fischer apparently doesn't realize that because to him "If
there's a 32-bit channel then the math is 32 bits." and "32 bits is
still 32 bits whether it's foating point or fixed point or integer."

Apparently he doesn't realize that telling a software engineer "it's
32 bits so the math is 32 bits" is meaningless if you actually have to
do something with that data other than store or ship it.

It could
be integer, scaled integer, floating point, etc., all of which are
completely different to a real software engineer.

And how would you know?

By the way: "Scaled integer"? No such thing. Unless you meant
fixed
point?

"Scaled integer" seems to be the new geekspeak for scientific
notation.

Sort of but not really because scientific notation allows for a
floating point significand, or mantissa. If you constrained the
mantissa to integers of a certain size and the exponent is a power of
2, not 10, then that would be scaled integer.

It's fixed point math except the binary point is allowed to float and
the programmer has to keep track of where it is after every operation
by keeping a scale factor with the data and properly setting the scale
factor of the result based on the input scale factors. You have to
have code to look for overflows and underflows and adjust the scale
factors accordingly so that you're using all the available bits most
effectively.

Or, if you know apriori what the range of values you'll be getting,
you can just assign a fixed scale to each stage of the calculations
and not worry about checking for over/under flow and adjusting the
scale factor. But you still have to keep track of where the binary
point is so that at the end of the chain of calculations, you know
what your resulting data represents.

Steve
.

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