Response curve in the photosphere

Response curve in the photosphere
Hello everybody!
I’m starting studies on HDR images. I still have many doubts. I made a set of LDR images with different exposures. I’m using Photosphere to generate the HDR image. Right now I’m trying to get the camera response curve (Nikon D90 and SIGMA 4.5 lens). However, I cannot find the txt file that contains the data for the camera response curve. Is this file not being generated for some reason? Or, I just can’t find it?

Thank you in advance for your attention.

Eliana

The camera response functions are saved in the “Library/Preferences/Photosphere” preferences file relative to your home directory on the Mac. I don’t remember where it gets put under Windows. The data is towards the end of the file, and looks like this:

CameraResponses = {
Make|Model|Version|Red|Green|Blue
"OLYMPUS OPTICAL CO.,LTD"|"E-10"|"42-0120"|{6.779350e-03,5.516785e-02,1.459309e+00,-2.929798e+00,2.408542e+00}|{6.390592e-03,8.606410e-02,1.246319e+00,-2.558258e+00,2.219484e+00}|{9.248151e-03,-9.216650e-03,1.786828e+00,-3.596076e+00,2.809217e+00}
"OLYMPUS OPTICAL CO.,LTD"|"C3030Z"|"v351u-76"|{3.396002e-03,3.315698e-01,-6.014519e-01,1.266486e+00}|{-4.601155e-03,3.578716e-01,-6.034859e-01,1.250215e+00}|{-7.762327e-03,4.018562e-01,-7.067782e-01,1.312684e+00}
} // CameraResponses

Not all that easy to read, but the polynomial coefficients are listed for red, green, and blue channels, respectively for the named cameras. Coefficients go from constant to higher orders, so “{-7.762327e-03,4.018562e-01,-7.067782e-01,1.312684e+00}” above corresponds to:

resp(x) = -7.762327e-03 + 4.018562e-01x + -7.067782e-01xx + 1.312684e+00xxx

Note that this order is reversed from that in hdrgen’s response curve file, and the order of the fit is implied by the number of coefficients (e.g., 4 coefficients == 3rd order polynomial).

Hope this helps!
-Greg

Dear Greg_Ward,
Thank you for the quick answer.
I believe I had some problem when installing Photosphere, this text file does not exist. Is it a .txt file? Is this file named in any specific way?

Thank you in advance.

Eliana

I have another question…
I have images in NEF format. Can I use them in Photosphere?

On Windows, the file is located in c:\Users\YourUserName\AppData\Roaming\photosphere\Library\Preferences\ and is named Photosphere (without extension), but it is just a plain text file.

Sorry for the lack of knowledge, but can I use the Photosphere software on windows system?

First, the file is relative to your HOME directory, not the system root. Also, the Library folder is invisible in the Finder by default, which makes it hard to find by normal means. From the Terminal, you can issue:

cd
more Library/Preferences/Photosphere

Regarding NEF format, this is not standardized and can be any of a number of subformats, which is why Photosphere doesn’t handle them directly. However, there is a program called dcraw that can handle many (though not all and not the most recent) camera RAW formats. This tool is used together with exiftool and hdrgen (derived from Photosphere) by the raw2hdr Perl script to create HDR images on the command line from RAW files, and is a very reliable way to perform this operation. This is advertised as the “command-line HDR builder” on anyhere.com, and is available for macOS and Linux.

As far as the Windows version goes, it is available but it is not free. A site license costs $250 US.

Best,
-Greg