132 lines
4.2 KiB
Markdown
132 lines
4.2 KiB
Markdown
libvips 8.4 should be out by the end of September 2016. This page introduces the main features.
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## New operators
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There are some fun new operators. `vips_perlin()` and `vips_worley()`
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make Perlin and Worley noise. They are useful for generating
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synthetic random textures. The implementations in vips can generate images of
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any size very quickly.
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## Rewritten convolution
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The convolution functions were the old vips7 ones with a small
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wrapper. They've now been rewritten for vips8, and the vector path has
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been completely replaced. It can be up to about 2x faster.
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The old vips7 vector path was based on int arithmetic, so this mask
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(a simple 3x3 average), for example:
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```
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3 3 9 0
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1 1 1
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1 1 1
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1 1 1
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```
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Would be computed as nine adds, followed by a divide by the constant 9,
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with round-to-nearest. This was obviously accurate, but dividing
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by a constant is slow.
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The new path first computes a fixed-point float approximation of the
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int mask. In this case it'll settle on this:
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```
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3 3 1 0
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3 3 3
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3 4 4
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4 4 4
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```
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Where 3 is approximately 1/9 in 3.5 bit fixed-point, and the whole
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mask sums to 1.0 (the sum of the int mask), or 32 in 3.5 bit.
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It's not possible to match each element and the sum at the same time,
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so vips uses an iterative algorithm to find the approximation that
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matches the sum exactly, matches each element as well as it can, and
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which spreads any error through the mask. In this case, the mix of 3 and 4
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is there to make the sum work. There's an error test and a fallback:
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if the maximum possible error is over 10%, it'll switch to a non-vector
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path based on exact int arithmetic. You can use `--vips-info` to see
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what path ends up being taken.
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Now there's a fixed-point version of the mask, vips can compute the
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convolution as 9 fused multiply-adds, followed by an add and a 5-bit shift
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to get back to the nearest int. Getting rid of the divide-by-a-constant
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gives a nice speed improvement. On my laptop with vips 8.3 and a 10k x 10k
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pixel RGB image I see:
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```
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$ time vips conv wtc.v x7.v avg.mat --vips-info
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real 0m1.311s
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user 0m1.376s
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sys 0m0.372s
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```
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With vips 8.4 it's now:
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```
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$ time vips convi wtc.v x8.v avg.mat --vips-info
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info: convi: using vector path
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real 0m0.774s
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user 0m0.888s
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sys 0m0.352s
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```
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The peak error is small:
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```
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$ vips subtract x7.v x8.v x.v
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$ vips abs x.v x2.v
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$ vips max x2.v
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11.000000
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```
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## Image resize
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`vips_resize()` has seen some good improvements.
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* There's a new `centre` option which switches over to centre-convention for
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subsampling. This makes it a much better match for ImageMagick.
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`vipsthumbnail` uses this new option.
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* It now does round-to-nearest when calculating image bounds. This makes it
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much simpler to calculate a shrink factor which will produce an image of a
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specific size.
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* A series of changes improve accuracy for the linear and cubic kernels, and
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improve spatial accuracy.
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* It used to simply use nearest for upsampling, in line with things like PDF,
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but this is not a good choice for many applications. It now upsizes with
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bicubic by default.
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## Unicode on Windows
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This is only a small thing, but the Windows build now supports Unicode
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filenames.
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## File format support
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As usual, there are a lot of improvements to file format read and write.
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* Thanks to work by Felix Bünemann, `webp` read and write supports many more
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options.
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* andris has improved `pdfload` so you can load many pages in a single
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operation.
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* Many people have worked on `dzsave` Google mode. It's now better at
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skipping blank tiles and supports tile overlaps. Felix Bünemann added
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support for compressed zip output.
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* Henri Chain has added `radsave_buffer` to improve Radiance support.
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* TIFF files with an orientation tag should now autorotate, `tiffsave`
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has better jpeg compression support, and it knows about the `strip`
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metadata option.
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* The load-via-libMagick operator now supports IM7.
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* The GIF loader is much smarter about guessing the number of colour channels.
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* PNG save supports `strip`.
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* The SVG loader supports `svgz` compressed files thanks to Felix Bünemann.
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## Other
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Improvements to the build system, reductions in memory use, many small
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bug fixes, improvements to the C++ binding, improvements to the Python binding,
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many small performance fixes. As usual, the ChanegLog has more detail if
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you're interested.
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