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removed the old whatsnew docs

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now part of the gh-pages blog
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whatsnew-8.4.md
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libvips 8.4 should be out by the end of September 2016. This page introduces the main features.
## New operators
There are some fun new operators. `vips_perlin()` and `vips_worley()`
make Perlin and Worley noise. They are useful for generating
synthetic random textures. The implementations in vips can generate images of
any size very quickly.
Here's an example of a marble texture simulated with a Perlin noise generator
using the Ruby libvips binding.
```
#!/usr/bin/ruby
require 'vips'
size = 1024
# perlin's "turbulence" image
def turbulence(size)
layers = []
iterations = Math.log(size, 2) - 2
(0 ... iterations).each do |i|
layer = Vips::Image.perlin(size, size, :cell_size => size / 2 ** i)
layer = layer.abs * (1.0 / (i + 1))
layers << layer
end
layers.reduce(:+)
end
# make a 256 element colour map: a linear fade from start to stop, with
# start and stop as CIELAB colours, the output map as sRGB
def gradient(start, stop)
lut = Vips::Image.identity / 255
lut = lut * start + (lut * -1 + 1) * stop
lut.colourspace(:srgb, :source_space => :lab)
end
# an image where the pixel value is 0 .. 4 * 360 across
angles = Vips::Image.xyz(size, size)[0] * 360 * 4 / size
# make a turbulent stripe pattern using 0 .. 255
stripe = ((angles + turbulence(size) * 700).sin + 1) * 128
# make a colour map (a smooth gradient from white to dark brown) then map
# our turbulent image through it
dark_brown = [7.45, 4.3, 8]
white = [100, 0, 0]
stripe = stripe.maplut(gradient(dark_brown, white))
stripe.write_to_file ARGV[0]
```
## Rewritten convolution
The convolution functions were the old vips7 ones with a small
wrapper. They've now been rewritten for vips8, and the vector path has
been completely replaced. It can be up to about 2x faster.
The old vips7 vector path was based on int arithmetic, so this mask
(a simple 3x3 average), for example:
```
3 3 9 0
1 1 1
1 1 1
1 1 1
```
Would be computed as nine adds, followed by a divide by the constant 9,
with round-to-nearest. This was obviously accurate, but dividing
by a constant is slow.
The new path first computes a fixed-point float approximation of the
int mask. In this case it'll settle on this:
```
3 3 1 0
3 3 3
3 4 4
4 4 4
```
Where 3 is approximately 1/9 in 3.5 bit fixed-point, and the whole
mask sums to 1.0 (the sum of the int mask), or 32 in 3.5 bit.
It's not possible to match each element and the sum at the same time,
so vips uses an iterative algorithm to find the approximation that
matches the sum exactly, matches each element as well as it can, and
which spreads any error through the mask. In this case, the mix of 3 and 4
is there to make the sum work. There's an error test and a fallback:
if the maximum possible error is over 10%, it'll switch to a non-vector
path based on exact int arithmetic. You can use `--vips-info` to see
what path ends up being taken.
Now there's a fixed-point version of the mask, vips can compute the
convolution as 9 fused multiply-adds, followed by an add and a 5-bit shift
to get back to the nearest int. Getting rid of the divide-by-a-constant
gives a nice speed improvement. On my laptop with vips 8.3 and a 10k x 10k
pixel RGB image I see:
```
$ time vips conv wtc.v x7.v avg.mat --vips-info
real 0m1.311s
user 0m1.376s
sys 0m0.372s
```
With vips 8.4 it's now:
```
$ time vips convi wtc.v x8.v avg.mat --vips-info
info: convi: using vector path
real 0m0.774s
user 0m0.888s
sys 0m0.352s
```
The peak error is small:
```
$ vips subtract x7.v x8.v x.v
$ vips abs x.v x2.v
$ vips max x2.v
11.000000
```
## Image resize
`vips_resize()` has seen some good improvements.
* There's a new `centre` option which switches over to centre-convention for
subsampling. This makes it a much better match for ImageMagick.
`vipsthumbnail` uses this new option.
* It now does round-to-nearest when calculating image bounds. This makes it
much simpler to calculate a shrink factor which will produce an image of a
specific size.
* A series of changes improve accuracy for the linear and cubic kernels, and
improve spatial accuracy.
* It used to simply use nearest for upsampling, in line with things like PDF,
but this is not a good choice for many applications. It now upsizes with
bicubic by default.
## Unicode on Windows
This is only a small thing, but the Windows build now supports Unicode
filenames.
## File format support
As usual, there are a lot of improvements to file format read and write.
* Thanks to work by Felix Bünemann, `webp` read and write supports many more
options.
* andris has improved `pdfload` so you can load many pages in a single
operation.
* Many people have worked on `dzsave` Google mode. It's now better at
skipping blank tiles and supports tile overlaps. Felix Bünemann added
support for compressed zip output.
* Henri Chain has added `radsave_buffer` to improve Radiance support.
* TIFF files with an orientation tag should now autorotate, `tiffsave`
has better jpeg compression support, and it knows about the `strip`
metadata option.
* The load-via-libMagick operator now supports IM7.
* The GIF loader is much smarter about guessing the number of colour channels.
* PNG save supports `strip`.
* The SVG loader supports `svgz` compressed files thanks to Felix Bünemann.
## Other
Improvements to the build system, reductions in memory use, many small
bug fixes, improvements to the C++ binding, improvements to the Python binding,
many small performance fixes. As usual, the ChanegLog has more detail if
you're interested.

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whatsnew-8.5.md
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libvips 8.5 should be out by the end of March 2017. This page introduces the
main features.
## New operators
Almost all of the logic from the `vipsthumbnail` program is now in a pair of
new operators, `vips_thumbnail()` and `vips_thumbnail_buffer()`. These are very
handy for the various scripting languages with vips bindings: you can now make
a high-quality, high-speed thumbnail in PHP (for example) with just:
```php
$filename = ...;
$image = Vips\Image::thumbnail($filename, 200, ["height" => 200]);
$image.writeToFile("my-thumbnail.jpg");
```
The new thumbnail operator has also picked up some useful features:
* **Smart crop** A new cropping mode called `attention` searches the image for
edges, skin tones and areas of saturated colour, and attempts to position the
crop box over the most significant feature. There's a `vips_smartcrop()`
operator as well.
* **Crop constraints** Thanks to tomasc, libvips has crop constraints. You
can set it to only thumbnail if the image is larger or smaller than the target
(the `<` and `>` modifiers in imagemagick), and to crop to a width or height.
* **Buffer sources** `vips_thumbnail_buffer()` will thumbnail an image held as
a formatted block of data in memory. This is useful for cloud services, where
the filesystem is often rather slow.
CLAHE, or Contrast-Limited Adaptive Histogram Equalisation, is a simple way to
make local histogram equalisation more useful.
Plain local equalization removes
all global brightness variation and can make images hard to understand.
The `hist_local` operator now has a `max-slope` parameter you can use to limit
how much equalisation can alter your image. A value of 3 generally works well.
## Toilet roll images
libvips used to let you pick single pages out of multi-page images, such
as PDFs, but had little support for processing entire documents.
libvips 8.5 now has good support for toilet roll images. You can load a
multipage image as a very tall, thin strip, process the whole thing, and write
back to another multi-page file. The extra feature is an `n` parameter which
gives the number of pages to load, or -1 to load all pages.
For example, (OME-
TIFF)[https://www.openmicroscopy.org/site/support/ome-model/ome-tiff]
is a standard for microscopy data that stores volumetric images as multi-page
TIFFs. They have some (sample
data)[https://www.openmicroscopy.org/site/support/ome-model/ome-tiff/data.html]
including a 4D image of an embryo.
Each TIFF contains 10 slices. Normally you just see page 0:
```
$ vipsheader tubhiswt_C0_TP13.ome.tif
tubhiswt_C0_TP13.ome.tif: 512x512 uchar, 1 band, b-w, tiffload
```
Use `n=-1` and you see all the pages as a very tall strip:
```
$ vipsheader tubhiswt_C0_TP13.ome.tif[n=-1]
tubhiswt_C0_TP13.ome.tif: 512x5120 uchar, 1 band, b-w, tiffload
```
You can work with PDF, TIFF, GIF and all imagemagick-supported formats in
this way.
You can write this tall strip to another file, and it will be broken up into
pages:
```
$ vips copy tubhiswt_C0_TP13.ome.tif[n=-1] x.tif
$ vipsheader x.tif
x.tif: 512x512 uchar, 1 band, b-w, tiffload
$ vipsheader x.tif[n=-1]
x.tif: 512x5120 uchar, 1 band, b-w, tiffload
```
The extra magic is a `page-height` property that images carry around that says
how long each sheet of toilet paper is.
There are clearly some restrictions with this style of multi-page document
handling: all pages must have identical width, height and colour depth; and image
processing operators have no idea they are dealing with a multi-page document,
so if you do something like `resize`, you'll need to update `page-height`.
You'll also need to be careful about edge effects if you're using spatial
filters.
## Computation reordering
Thanks to the developer of
(PhotoFlow)[https://github.com/aferrero2707/PhotoFlow], a non-destructive image
editor with a libvips backend, libvips can now reorder computations to reduce
recalculation. This can (sometimes) produce a dramatic speedup.
This has been (discussed on the libvips
blog)[http://libvips.blogspot.co.uk/2017/01/automatic-computation-reordering.html],
but briefly, the order in which operator arguments are evaluated can have a
big effect on runtime due to the way libvips tries to cache and reuse results
behind the scenes.
The blog post has some examples and some graphs.
## New sequential mode
libvips sequential mode has been around for a while. This is the thing libvips
uses to stream pixels through your computer, from input file to output file,
without having to have the whole image in memory all at the same time. When it
works, it give a nice performance boost and a large drop in memory use.
There are some more complex cases where it didn't work. Consider this Python
program:
```python
#!/usr/bin/python
import sys
import random
import gi
gi.require_version('Vips', '8.0')
from gi.repository import Vips
composite = Vips.Image.black(10000, 10000)
for filename in sys.argv[2:]:
tile = Vips.Image.new_from_file(filename, access = Vips.Access.SEQUENTIAL)
x = random.randint(0, composite.width - tile.width)
y = random.randint(0, composite.height - tile.height)
composite = composite.insert(tile, x, y)
composite.write_to_file(sys.argv[1])
```
It makes a large 10,000 x 10,000 pixel image, then inserts all of the images
you list at random positions, then writes the result.
You'd think this could work with sequential mode, but sadly with earlier
libvipses it will sometimes fail. The problem is that images can cover each
other, so while writing, libvips can discover that it only needs the bottom few
pixels of one of the input images. The image loaders used to track the current
read position, and if a request came in for some pixels way down the image,
they'd assume one of the evaluation threads had run ahead of the rest and
needed to be stalled. Once stalled, it was only restarted on a long timeout,
causing performance to drop through the floor.
libvips 8.5 has a new implementation of sequential mode that changes the way
threads are kept together as images are processed. Rather than trying to add
constraints to load operations, instead it puts the constraints into operations
that can cause threads to become spread out, such as vertical shrink.
As a result of this change, many more things can run in sequential mode, and
out of order reads should be impossible.
## `libxml2` swapped out for `expat`
libvips has used libxml2 as its XML parser since dinosaurs roamed the Earth.
Now libvips is based on gobject, the XML parser selected by glib, expat, makes
more sense, since it will already be linked.
It's nice to be able to remove a required dependency for a change.
## File format support
As usual, there are a range of improvements to file format read and write.
* Thanks to a push from Felix Bünemann, TIFF now supports load and save to and
from memory buffers.
* `dzsave` can write to memory (as a zip file) as well.
* Again, thanks to pushing from Felix, libvips now supports ICC, XMP and IPCT
metadata for WebP images.
* FITS images support `bzero` and `bscale`.
* `tiffload` memory use is now much lower for images with large strips.
## Other
Many small bug fixes, improvements to the C++ binding. As usual, the
ChangeLog has more detail, if you're interested.