# hdrgen rsp coefficients

Hi Greg, hi everyone else,

This is an example of an rsp file (Optio 430):
3 1.44593 -0.999398 0.575389 -0.0219197
3 1.23165 -0.639997 0.413386 -0.00504164
3 1.07103 -0.436035 0.351256 0.0137438

Is it correct to assume that the 1st coefficient is the highest one (3rd
order in this case), so would the formula be (for Red channel):

'PENTAX Optio 430 '
1.44593*x**3 + -0.999398*x**2 + 0.575389*x + -0.0219197

If so, then this is a plot for some cams I've created with gnuplot (again
Red only):
http://luminance.londonmet.ac.uk/pickup/rsp_gnuplot.png

If plotted for x [0:255], that would give a dynamic range of 7 log units
for one photograph. Seem a bit excessive. Am I missing some important
detail here?

Cheers

Axel

Hi Axel,

Your interpretation of the coefficients is correct, but the [0-255] values are converted to a [0-1] range being put into the polynomials. This would account for your odd results.

-Greg

···

From: "Axel Jacobs" <a.jacobs@londonmet.ac.uk>
Date: April 26, 2006 8:00:54 AM PDT

Hi Greg, hi everyone else,

This is an example of an rsp file (Optio 430):
3 1.44593 -0.999398 0.575389 -0.0219197
3 1.23165 -0.639997 0.413386 -0.00504164
3 1.07103 -0.436035 0.351256 0.0137438

Is it correct to assume that the 1st coefficient is the highest one (3rd
order in this case), so would the formula be (for Red channel):

'PENTAX Optio 430 '
1.44593*x**3 + -0.999398*x**2 + 0.575389*x + -0.0219197

If so, then this is a plot for some cams I've created with gnuplot (again
Red only):
http://luminance.londonmet.ac.uk/pickup/rsp_gnuplot.png

If plotted for x [0:255], that would give a dynamic range of 7 log units
for one photograph. Seem a bit excessive. Am I missing some important
detail here?

Cheers

Axel