[Openexr-devel] Huge Files & Tiles

[Gordon Wetzstein]

Dear OpenEXR developers,

I am using OpenEXR for reading and writing simple floating point images for
quite a while now and I am totally happy with it. Recently, I started
working with huge amounts of data, let's say an image has a resolution of
640x480 by 1024x768. Until now I stored every column of these images in
separate files, resulting a many files that are very slow to read and
cumbersome to handle anyway. I have to process the data, so the problem is
to hold all of it in the main memory. Actually this is possible but not very
convenient. My idea was to swap all the data onto the harddisk in one file
using a tiled EXR image and only use the data that I currently need. This
didn't work out as I wanted it to, thus I have a couple of questions (I use
the C-Interface because I could not link EXR to our software)

1. Is it possible to allocate an array of ImfRgba that is as big as one tile
and read and write only a particular tile from/to the
ImfTiledInputFile/ImfTiledOutputFile into it. I cannot set the data window
of the input file, which makes sense, but it seems that I have to allocate
an array of the complete size of the image and can read in tiles into the
framebuffer. This is not nice, because I waste a lot of memory, if I only
want to process one tile at a time.

2. It thought to store each column as a tile, which would allow to read the
individual columns. However, it would be fantastic to be able to read
individual rows as well, even after I stored the tiles as columns. The same
for writing the data. What I need is one big file, that allows reading
arbitrary rectangles and storing them back in the file without reading the
whole data and allocating a complete framebuffer.

So my question: is the tiled EXR image format the right thing for me or does
anyone have alternative suggestions? I would appreciate any hint.

Kind Regards,

Gordon Wetzstein
Media System Science
Faculty of Media
Bauhaus-University Weimar

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