Hi Yulia,
Not all of the options of hdrgen are relevant for raw2hdr. See inline....
> From: "Tyukhova, Yulia" <[email protected]>
> Date: February 21, 2012 1:21:05 PM PST
>
> Greg,
>
> Following up your suggestions...
>
> I was able to run your scripts, but now I have more questions on what's
> behind them.
>
> 1. I assume after combining raw images into one, I can analyze obtained hdr
> image in Photosphere.
Yes, of course.
> >> –r cam.rsp
> Use the given file for the camera’s response curves. If this file exists, it
> must contain the coefficients of three polynomials, one for each color
> primary. If the file does not exist, hdrgen will use its principal algorithm
> to derive these coefficients and write them out to this file for later use.
>
> 2. So, if I will combine my images for the calibration scene, hdrgen will
> derive the coefficients to the file. Is there a way to see those coefficients
> and to know what the response curve looks like?
The raw2hdr script doesn't need to derive a response curve, since the sensor
data is linear. Instead, it creates an output from dcraw that follows a 2.0
gamma and creates an artificial response curve of x^2 to decode it. This
reduces quantization errors from the 8-bit intermediate images.
> >>The -C option is to provide a linear factor to correct the overall exposure
> >>based on previous calibrations.
>
> 3. How do I make the absolute calibration? Usually it is a luminance value of
> a reflectance standard measured with luminance meter applied in Photosphere.
> But how do I do it with the given script?
Look at your raw2hdr result in Photosphere and select the measured area.
Divide your measurement by the value Photosphere gives you. This is the
calibration factor to use with the -C option for conversions for this camera
and lens.
> >>The -c option is to specify an output color space. The default is "sRGB"
> >>which is actually linear CCIR-709 primaries. The only other output color
> >>space I would recommend is AdobeRGB. There is a CIE XYZ space supported by
> >>dcraw, but I have found it to be somewhat unreliable, and I don't know
> >>where the fault lies in this.
>
> 4. In order to have luminance values Photosphere has an algorithm that does
> color calculations from sRGB to CIE XYZ (standard illuminant D65), where Y is
> the luminance value. Here I can specify an output color space, let's say
> sRGB, but how would I get luminance values?
As I mentioned, the sRGB and AdobeRGB spaces will both work, and Photosphere
will adjust its Y value calculations accordingly. The color space is recorded
in the HDR output.
> >>–s stonits
>
> 5.What is this option about?
You do not need it -- this option is for when the camera doesn't record the
necessary aperture, asa and shutter speed settings in the image file.
Best,
-Greg
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