add 'reverse_axes' options to Buffer conversions #7127
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(LMK if this would be easier to review if I went ahead and combined it with #7125) |
abadams
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Oct 27, 2022
steven-johnson
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* Fix Python buffer handling In the category of "how did this ever work"... TL;DR: in general, Halide Buffers have the opposite axis ordering from Python/NumPy buffers; in Halide, the most-frequently-varying dimension comes first, while in Python, it comes last. This isn't surprising, though, since Halide's indexing scheme is effectively column-major while NumPy's is row-major. Anyway: what we *should* have done was to reverse the order of dimensions when converting to/from Halide Buffers vs Python buffers; instead, we kept the same order, then jumped thru hoops to rearrange buffers to fit this setup. This PR does the appropriate axis reordering, fixing the apps and tests as needed. It also adds some helper code for image reading and writing; by default, we use `imageio` for this, but imageio ~always wants RGB/RGBA images to be interleaved (vs the planar that Halide prefers). So, I added the `halide.imageio` package, that has wrapper functions to quietly convert to/from planar as needed. Needless to say, this change is likely to break existing code that is using 3d buffers in Halide, but I think it's the right long-term thing to do. Opinions greatly welcomed here. * Update PyBuffer.cpp * -"for better vectorization" * public halide.imageio utilities should copy() buffers * PEP8 * Update imageio.py * Update imageio.py * add 'reverse_axes' options to Buffer conversions (#7127) * add 'reverse_axes' options to Buffer conversions
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* Fix Python buffer handling In the category of "how did this ever work"... TL;DR: in general, Halide Buffers have the opposite axis ordering from Python/NumPy buffers; in Halide, the most-frequently-varying dimension comes first, while in Python, it comes last. This isn't surprising, though, since Halide's indexing scheme is effectively column-major while NumPy's is row-major. Anyway: what we *should* have done was to reverse the order of dimensions when converting to/from Halide Buffers vs Python buffers; instead, we kept the same order, then jumped thru hoops to rearrange buffers to fit this setup. This PR does the appropriate axis reordering, fixing the apps and tests as needed. It also adds some helper code for image reading and writing; by default, we use `imageio` for this, but imageio ~always wants RGB/RGBA images to be interleaved (vs the planar that Halide prefers). So, I added the `halide.imageio` package, that has wrapper functions to quietly convert to/from planar as needed. Needless to say, this change is likely to break existing code that is using 3d buffers in Halide, but I think it's the right long-term thing to do. Opinions greatly welcomed here. * Update PyBuffer.cpp * -"for better vectorization" * public halide.imageio utilities should copy() buffers * PEP8 * Update imageio.py * Update imageio.py * add 'reverse_axes' options to Buffer conversions (#7127) * add 'reverse_axes' options to Buffer conversions
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ardier
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* Fix Python buffer handling In the category of "how did this ever work"... TL;DR: in general, Halide Buffers have the opposite axis ordering from Python/NumPy buffers; in Halide, the most-frequently-varying dimension comes first, while in Python, it comes last. This isn't surprising, though, since Halide's indexing scheme is effectively column-major while NumPy's is row-major. Anyway: what we *should* have done was to reverse the order of dimensions when converting to/from Halide Buffers vs Python buffers; instead, we kept the same order, then jumped thru hoops to rearrange buffers to fit this setup. This PR does the appropriate axis reordering, fixing the apps and tests as needed. It also adds some helper code for image reading and writing; by default, we use `imageio` for this, but imageio ~always wants RGB/RGBA images to be interleaved (vs the planar that Halide prefers). So, I added the `halide.imageio` package, that has wrapper functions to quietly convert to/from planar as needed. Needless to say, this change is likely to break existing code that is using 3d buffers in Halide, but I think it's the right long-term thing to do. Opinions greatly welcomed here. * Update PyBuffer.cpp * -"for better vectorization" * public halide.imageio utilities should copy() buffers * PEP8 * Update imageio.py * Update imageio.py * add 'reverse_axes' options to Buffer conversions (halide#7127) * add 'reverse_axes' options to Buffer conversions
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This adds some options to the changes in #7127 to allow for easier backwards compatibility with previous versions of the Python bindings:
hl.Bufferfrom a Python buffer is to reverse the axes. There is now an optional named arg to that ctor that you can specifyreverse_axes = Falseif you want the behavior of pre-Halide-15 (ie, don't reverse).np.array,np.ndarrayetc from anhl.Bufferis to reverse the axes. There is now a new method onhl.Buffer,reverse_axes(), which simply returns another Buffer that is a view onto the same memory, but with the order of the axes reverse. This allows you to keep the behavior of pre-Halide-15 (ie, don't reverse) by doing something likenp.array(halidebug.reverse_axes(), ...).