Merge multiple EXR files into one single EXR file

Discussions on NConvert - the command line tool for image conversion and manipulation

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Merge multiple EXR files into one single EXR file

Post by fredrik »

I have found NConvert to be a really useful application and just purchased a business license. I have one certain need however, which NConvert currently can't do -- and that is to be able to merge multiple EXR image files into one singe EXR image file (using e.g. a regular "over", A+B operation for all channels). And I have yet to find a simple commandline solution which I can run on both Windows and Linux machines.

I work in 3D visualization and render out images in the OpenEXR format. In order to speed up the rendering of a large still image, we split the image up in e.g. 64 tiles and render each tile on our render farm which consists of a mix of Windows and Linux machines. When all 64 tiles are done, we need to put them together into one single EXR file. For this last step, I would have loved to be able to use NConvert by giving it 64 exr files as input and output one single exr file.

Today, we use a Windows-only OpenImageIO Python binding and there are also numerous other ways of solving this - but they all involve some amount of complexity or manual labour. Are there any plans on making it possible to merge such EXR files together using NConvert -- or would you consider developing such a feature or new commandline-based application?

Functionality details explained:
  • We would need the merged EXR file to be using "Zip (1 scanline)" compression and with datatype "16-bit half", and so it could be useful to provide options to use the common compression types () and datatypes (16-bit half or 32-bit float).
  • The OpenEXR format dictates the full image size canvas, so there is no need to provide tile coordinates. You just need to read the 64 image buffers and combine them, in layman terms.
I could provide you with EXR images which we have "tile rendered" and would like to merge into one single EXR file if you would be interested in implenting such a feature.

I'm on the border of hiring a C++ programmer to solve this for us, but I would much rather see this be supported by NConvert.

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Re: Merge multiple EXR files into one single EXR file

Post by xnview »

Sorry currently not in the TODO list... I can check if it's easy, but currently i have not the time... :(