CS 348B - Computer Graphics: Image Synthesis Techniques

exrtotiff -- Bug and workaround (4/29/2004)

If you are working on Linux or OSX, then the exrtotiff executable may be causing you problems on HW3. 

Workaround synopsis

Please use /usr/class/cs348b/files/exrtotiff with parameter -bg 0.001.  For example, to convert file.exr to file.tiff, use '/usr/class/cs348b/files/exrtotiff -bg 0.001 file.exr file.tiff'.  Note that this is only for Linux.  The OSX binary is at /usr/class/cs348b/files/exrtotiff.osx.gz..

Symptoms of the bug

There appears to be a bug that has to do with the way exrtotiff handles premultiplied alpha, which can generate large errors in output tiff pixel values. The output EXR file seems to be fine -- just the conversion to tiff produces problems.  The following images illustrate the symptoms of the problem, to help you figure out whether this bug has been affecting you:


The left image was created with the version of exrtotiff in the pbrtsrc that you have been using since Homework 1.  The right image was produced with the newer /usr/class/cs348b/files/exrtotiff with parameter -bg 0.001. 

The original exr for both of these is exrtotiff.exr, and the corresponding tiff files are exrtotiff.tiff and exrtotiff.new.tiff.