proper use of pcond and ximage

I am trying to map a scene (not rendered with Radiance, but saved as RGBE pic)using the histogram method with pcond.
Who can I map luminance values not from black to white but from dark
to white. Clearly shadows areas are not black, the output of pextrem is like that:
469 73 5.702972e-04 5.702972e-04 5.702972e-04
311 652 7.402344e-01 7.402344e-01 7.402344e-01

I can do it with linear mapping, but my purpose is really to use
the histogram method!!

This problem seems to be relevant to almost any scene.

Thanks for any advice.

Frederic Drago

···

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Hi Frederic,

I'm not sure what you are asking, exactly, but pcond should work
fine as long as you give it a valid Radiance picture. The
command syntax is simple:

% pcond input.pic > output.pic

There are a bunch of options for simulating human visibility, etc.,
but you probably should avoid them if your input image isn't
calibrated (i.e., if it doesn't have a valid EXPOSURE= line
in the header, which you can read with the getinfo command).

Another program that performs a simpler, faster histogram adjustment
is normtiff, which takes a Radiance or LogLuv TIFF input and produces
a 24-bit RGB TIFF output. It's syntax is:

% normtiff input output.tif

The minimum value in the image will be mapped to the minimum value
of the display, which is determined by the dynamic range given in
the -d option (default is 32). This comes out as 0 in the 0-255
range. If you don't want black output values, then you will have
to use a different algorithm or modify the source code of this one.
But why wouldn't you want to use the full display range available?
Do you have a specific application need you aren't telling us about?

-Greg

···

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Frederic Drago writes:

I am trying to map a scene (not rendered with Radiance, but saved as RGBE
pic)using the histogram method with pcond.
Who can I map luminance values not from black to white but from dark
to white. Clearly shadows areas are not black, the output of pextrem is like
that:
469 73 5.702972e-04 5.702972e-04 5.702972e-04
311 652 7.402344e-01 7.402344e-01 7.402344e-01

I can do it with linear mapping, but my purpose is really to use
the histogram method!!

This problem seems to be relevant to almost any scene.

Thanks for any advice.

Frederic Drago