Inconsistent width scaling

[kaspergrubbe]

Describe the bug

When scaling images to 100x33 I get random results, I know it was already discussed here: #150, libvips/libvips#709 and libvips/libvips#1639 but maybe we should discuss if we can make it more consistent? It also seems like the behavior/math is different based on image type (in jpeg2000 case)?

When I scale with 100x I (for the most part) get 100x33 images, but when I scale with 100x33 I get 99x33 images, I guess users expect to get a 100x33 image when scaling to 100x33, I am aware of the hack described in #150 when width is more important than height:

vips_image.thumbnail_image(resize_args[:width].to_i, height: Vips::MAX_COORD)

But maybe there's a better fix?

The .jp2 (sorry for keep bothering you with jpeg2000 examples) scales differently than the others:

Vipsthumbnail 100x33: 100x33
Libvipsrb 100x33: 99x33

To Reproduce

Images and code is attached here: example-images-and-code.zip

ENV['VIPS_CONCURRENCY'] = '1'
ENV['VIPS_NOVECTOR'] = '1'
ENV['VIPS_INFO'] = '1'

require 'bundler/inline'

gemfile do
  source 'https://rubygems.org'
  gem 'ruby-vips', '2.1.4'
end

require 'vips'

def vips_to_file(target_file)
  puts "# #{target_file}"
  filesplit = target_file.split('.')
  vipsthumbnail_100x33_filename = "#{filesplit[0]}-vipsthumbnail-100x33.#{filesplit[1]}"
  vipsthumbnail_100x_filename = "#{filesplit[0]}-vipsthumbnail-100x.#{filesplit[1]}"
  libvipsrb_100x33_filename = "#{filesplit[0]}-libvipsrb-100x33.#{filesplit[1]}"
  libvipsrb_100x_filename = "#{filesplit[0]}-libvipsrb-100x.#{filesplit[1]}"

  puts ''
  puts '## vipsthumbnail 100x33'
  puts ''
  puts '```'
  system "vipsthumbnail #{target_file} --vips-info --size 100x33 -o #{vipsthumbnail_100x33_filename}"
  puts '```'
  puts ''

  puts ''
  puts '## vipsthumbnail 100x'
  puts ''
  puts '```'
  system "vipsthumbnail #{target_file} --vips-info --size 100x -o #{vipsthumbnail_100x_filename}"
  puts '```'
  puts ''

  puts '## libvips ruby 100x33'
  puts ''
  puts '```'
  vips_image = Vips::Image.new_from_file(target_file)
  vips_image = vips_image.thumbnail_image(100, height: 33)
  vips_image.write_to_file(libvipsrb_100x33_filename)
  puts '```'
  puts ''

  puts '## libvips ruby 100x'
  puts ''
  puts '```'
  vips_image = Vips::Image.new_from_file(target_file)
  vips_image = vips_image.thumbnail_image(100)
  vips_image.write_to_file(libvipsrb_100x_filename)
  puts '```'
  puts ''

  puts '## Results'
  puts ''
  vips_image = Vips::Image.new_from_file(vipsthumbnail_100x33_filename)
  puts "Vipsthumbnail 100x33: #{vips_image.width}x#{vips_image.height}"
  puts ''
  vips_image = Vips::Image.new_from_file(libvipsrb_100x33_filename)
  puts "Libvipsrb 100x33: #{vips_image.width}x#{vips_image.height}"
  puts ''
  vips_image = Vips::Image.new_from_file(vipsthumbnail_100x_filename)
  puts "Vipsthumbnail 100x: #{vips_image.width}x#{vips_image.height}"
  puts ''
  vips_image = Vips::Image.new_from_file(libvipsrb_100x_filename)
  puts "Libvipsrb 100x: #{vips_image.width}x#{vips_image.height}"
  puts ''
end

vips_to_file('coverimage.jp2')
vips_to_file('coverimage.jpeg')
vips_to_file('coverimage.jxl')
vips_to_file('coverimage.png')
vips_to_file('coverimage.tiff')
vips_to_file('coverimage.webp')

Result

coverimage.jp2

vipsthumbnail 100x33

VIPS-INFO: 10:21:39.961: VIPSHOME = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:39.961: VIPS_PREFIX = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:39.961: VIPS_LIBDIR = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:39.961: prefix = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:39.961: libdir = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:39.962: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13"
VIPS-INFO: 10:21:39.962: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-jxl.so"
VIPS-INFO: 10:21:39.964: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-poppler.so"
VIPS-INFO: 10:21:39.970: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-heif.so"
VIPS-INFO: 10:21:39.981: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-openslide.so"
VIPS-INFO: 10:21:39.985: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-magick.so"
VIPS-INFO: 10:21:39.988: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-plugins-8.13"
VIPS-INFO: 10:21:39.995: thumbnailing coverimage.jp2
VIPS-INFO: 10:21:40.007: selected loader is VipsForeignLoadJp2kFile
VIPS-INFO: 10:21:40.007: input size is 1273 x 423
VIPS-INFO: 10:21:40.009: loading with factor 2 pre-shrink
VIPS-INFO: 10:21:40.011: pre-shrunk size is 319 x 106
VIPS-INFO: 10:21:40.011: converting to processing space srgb
VIPS-INFO: 10:21:40.011: premultiplying alpha
VIPS-INFO: 10:21:40.011: residual reducev by 0.311321
VIPS-INFO: 10:21:40.011: reducev: 21 point mask
VIPS-INFO: 10:21:40.011: reducev sequential line cache
VIPS-INFO: 10:21:40.011: residual reduceh by 0.311321
VIPS-INFO: 10:21:40.011: reduceh: 21 point mask
VIPS-INFO: 10:21:40.012: unpremultiplying alpha
VIPS-INFO: 10:21:40.012: converting to output space srgb
VIPS-INFO: 10:21:40.012: thumbnailing coverimage.jp2 as ./coverimage-vipsthumbnail-100x33.jp2

vipsthumbnail 100x

VIPS-INFO: 10:21:40.088: VIPSHOME = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:40.088: VIPS_PREFIX = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:40.088: VIPS_LIBDIR = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:40.088: prefix = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:40.088: libdir = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:40.089: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13"
VIPS-INFO: 10:21:40.089: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-jxl.so"
VIPS-INFO: 10:21:40.091: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-poppler.so"
VIPS-INFO: 10:21:40.097: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-heif.so"
VIPS-INFO: 10:21:40.107: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-openslide.so"
VIPS-INFO: 10:21:40.111: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-magick.so"
VIPS-INFO: 10:21:40.114: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-plugins-8.13"
VIPS-INFO: 10:21:40.119: thumbnailing coverimage.jp2
VIPS-INFO: 10:21:40.124: selected loader is VipsForeignLoadJp2kFile
VIPS-INFO: 10:21:40.124: input size is 1273 x 423
VIPS-INFO: 10:21:40.126: loading with factor 2 pre-shrink
VIPS-INFO: 10:21:40.127: pre-shrunk size is 319 x 106
VIPS-INFO: 10:21:40.127: converting to processing space srgb
VIPS-INFO: 10:21:40.127: premultiplying alpha
VIPS-INFO: 10:21:40.127: residual reducev by 0.31348
VIPS-INFO: 10:21:40.127: reducev: 21 point mask
VIPS-INFO: 10:21:40.127: reducev sequential line cache
VIPS-INFO: 10:21:40.127: residual reduceh by 0.31348
VIPS-INFO: 10:21:40.128: reduceh: 21 point mask
VIPS-INFO: 10:21:40.128: unpremultiplying alpha
VIPS-INFO: 10:21:40.128: converting to output space srgb
VIPS-INFO: 10:21:40.128: thumbnailing coverimage.jp2 as ./coverimage-vipsthumbnail-100x.jp2

libvips ruby 100x33

VIPS-INFO: 10:21:40.162: selected loader is image source
VIPS-INFO: 10:21:40.162: input size is 1273 x 423
VIPS-INFO: 10:21:40.162: loading with factor 1 pre-shrink
VIPS-INFO: 10:21:40.162: pre-shrunk size is 1273 x 423
VIPS-INFO: 10:21:40.162: converting to processing space srgb
VIPS-INFO: 10:21:40.162: premultiplying alpha
VIPS-INFO: 10:21:40.162: residual reducev by 0.0780142
VIPS-INFO: 10:21:40.162: shrinkv by 6
VIPS-INFO: 10:21:40.162: reducev: 13 point mask
VIPS-INFO: 10:21:40.163: residual reduceh by 0.0780142
VIPS-INFO: 10:21:40.163: shrinkh by 6
VIPS-INFO: 10:21:40.163: reduceh: 13 point mask
VIPS-INFO: 10:21:40.163: unpremultiplying alpha
VIPS-INFO: 10:21:40.163: converting to output space srgb

libvips ruby 100x

VIPS-INFO: 10:21:40.343: selected loader is image source
VIPS-INFO: 10:21:40.343: input size is 1273 x 423
VIPS-INFO: 10:21:40.343: loading with factor 1 pre-shrink
VIPS-INFO: 10:21:40.343: pre-shrunk size is 1273 x 423
VIPS-INFO: 10:21:40.343: converting to processing space srgb
VIPS-INFO: 10:21:40.343: premultiplying alpha
VIPS-INFO: 10:21:40.343: residual reducev by 0.0785546
VIPS-INFO: 10:21:40.343: shrinkv by 6
VIPS-INFO: 10:21:40.343: reducev: 13 point mask
VIPS-INFO: 10:21:40.343: residual reduceh by 0.0785546
VIPS-INFO: 10:21:40.343: shrinkh by 6
VIPS-INFO: 10:21:40.343: reduceh: 13 point mask
VIPS-INFO: 10:21:40.343: unpremultiplying alpha
VIPS-INFO: 10:21:40.344: converting to output space srgb

Results

Vipsthumbnail 100x33: 99x33

Libvipsrb 100x33: 99x33

Vipsthumbnail 100x: 100x33

Libvipsrb 100x: 100x33

coverimage.jpeg

vipsthumbnail 100x33

VIPS-INFO: 10:21:40.552: VIPSHOME = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:40.552: VIPS_PREFIX = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:40.552: VIPS_LIBDIR = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:40.552: prefix = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:40.552: libdir = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:40.553: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13"
VIPS-INFO: 10:21:40.553: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-jxl.so"
VIPS-INFO: 10:21:40.555: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-poppler.so"
VIPS-INFO: 10:21:40.561: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-heif.so"
VIPS-INFO: 10:21:40.571: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-openslide.so"
VIPS-INFO: 10:21:40.576: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-magick.so"
VIPS-INFO: 10:21:40.579: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-plugins-8.13"
VIPS-INFO: 10:21:40.585: thumbnailing coverimage.jpeg
VIPS-INFO: 10:21:40.592: selected loader is VipsForeignLoadJpegFile
VIPS-INFO: 10:21:40.592: input size is 1273 x 423
VIPS-INFO: 10:21:40.592: loading with factor 4 pre-shrink
VIPS-INFO: 10:21:40.593: pre-shrunk size is 318 x 105
VIPS-INFO: 10:21:40.593: converting to processing space srgb
VIPS-INFO: 10:21:40.593: residual reducev by 0.314286
VIPS-INFO: 10:21:40.593: reducev: 21 point mask
VIPS-INFO: 10:21:40.593: reducev sequential line cache
VIPS-INFO: 10:21:40.593: residual reduceh by 0.314286
VIPS-INFO: 10:21:40.594: reduceh: 21 point mask
VIPS-INFO: 10:21:40.594: converting to output space srgb
VIPS-INFO: 10:21:40.594: thumbnailing coverimage.jpeg as ./coverimage-vipsthumbnail-100x33.jpeg

vipsthumbnail 100x

VIPS-INFO: 10:21:40.654: VIPSHOME = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:40.655: VIPS_PREFIX = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:40.655: VIPS_LIBDIR = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:40.655: prefix = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:40.655: libdir = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:40.655: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13"
VIPS-INFO: 10:21:40.656: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-jxl.so"
VIPS-INFO: 10:21:40.657: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-poppler.so"
VIPS-INFO: 10:21:40.663: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-heif.so"
VIPS-INFO: 10:21:40.674: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-openslide.so"
VIPS-INFO: 10:21:40.678: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-magick.so"
VIPS-INFO: 10:21:40.681: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-plugins-8.13"
VIPS-INFO: 10:21:40.686: thumbnailing coverimage.jpeg
VIPS-INFO: 10:21:40.690: selected loader is VipsForeignLoadJpegFile
VIPS-INFO: 10:21:40.690: input size is 1273 x 423
VIPS-INFO: 10:21:40.690: loading with factor 4 pre-shrink
VIPS-INFO: 10:21:40.691: pre-shrunk size is 318 x 105
VIPS-INFO: 10:21:40.691: converting to processing space srgb
VIPS-INFO: 10:21:40.691: residual reducev by 0.314465
VIPS-INFO: 10:21:40.691: reducev: 21 point mask
VIPS-INFO: 10:21:40.691: reducev sequential line cache
VIPS-INFO: 10:21:40.691: residual reduceh by 0.314465
VIPS-INFO: 10:21:40.691: reduceh: 21 point mask
VIPS-INFO: 10:21:40.692: converting to output space srgb
VIPS-INFO: 10:21:40.692: thumbnailing coverimage.jpeg as ./coverimage-vipsthumbnail-100x.jpeg

libvips ruby 100x33

VIPS-INFO: 10:21:40.701: selected loader is image source
VIPS-INFO: 10:21:40.701: input size is 1273 x 423
VIPS-INFO: 10:21:40.701: loading with factor 1 pre-shrink
VIPS-INFO: 10:21:40.701: pre-shrunk size is 1273 x 423
VIPS-INFO: 10:21:40.702: converting to processing space srgb
VIPS-INFO: 10:21:40.702: residual reducev by 0.0780142
VIPS-INFO: 10:21:40.702: shrinkv by 6
VIPS-INFO: 10:21:40.702: shrinkv sequential line cache
VIPS-INFO: 10:21:40.702: reducev: 13 point mask
VIPS-INFO: 10:21:40.702: reducev sequential line cache
VIPS-INFO: 10:21:40.702: residual reduceh by 0.0780142
VIPS-INFO: 10:21:40.702: shrinkh by 6
VIPS-INFO: 10:21:40.702: reduceh: 13 point mask
VIPS-INFO: 10:21:40.703: converting to output space srgb

libvips ruby 100x

VIPS-INFO: 10:21:40.727: selected loader is image source
VIPS-INFO: 10:21:40.727: input size is 1273 x 423
VIPS-INFO: 10:21:40.727: loading with factor 1 pre-shrink
VIPS-INFO: 10:21:40.727: pre-shrunk size is 1273 x 423
VIPS-INFO: 10:21:40.727: converting to processing space srgb
VIPS-INFO: 10:21:40.727: residual reducev by 0.0785546
VIPS-INFO: 10:21:40.727: shrinkv by 6
VIPS-INFO: 10:21:40.727: shrinkv sequential line cache
VIPS-INFO: 10:21:40.727: reducev: 13 point mask
VIPS-INFO: 10:21:40.727: reducev sequential line cache
VIPS-INFO: 10:21:40.727: residual reduceh by 0.0785546
VIPS-INFO: 10:21:40.727: shrinkh by 6
VIPS-INFO: 10:21:40.727: reduceh: 13 point mask
VIPS-INFO: 10:21:40.728: converting to output space srgb

Results

Vipsthumbnail 100x33: 100x33

Libvipsrb 100x33: 99x33

Vipsthumbnail 100x: 100x33

Libvipsrb 100x: 100x33

coverimage.jxl

vipsthumbnail 100x33

VIPS-INFO: 10:21:40.805: VIPSHOME = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:40.805: VIPS_PREFIX = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:40.805: VIPS_LIBDIR = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:40.805: prefix = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:40.805: libdir = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:40.806: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13"
VIPS-INFO: 10:21:40.806: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-jxl.so"
VIPS-INFO: 10:21:40.808: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-poppler.so"
VIPS-INFO: 10:21:40.814: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-heif.so"
VIPS-INFO: 10:21:40.825: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-openslide.so"
VIPS-INFO: 10:21:40.828: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-magick.so"
VIPS-INFO: 10:21:40.831: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-plugins-8.13"
VIPS-INFO: 10:21:40.837: thumbnailing coverimage.jxl
VIPS-INFO: 10:21:40.867: selected loader is VipsForeignLoadJxlFile
VIPS-INFO: 10:21:40.868: input size is 1273 x 423
VIPS-INFO: 10:21:40.868: loading with factor 1 pre-shrink
VIPS-INFO: 10:21:40.869: pre-shrunk size is 1273 x 423
VIPS-INFO: 10:21:40.869: converting to processing space srgb
VIPS-INFO: 10:21:40.869: premultiplying alpha
VIPS-INFO: 10:21:40.869: residual reducev by 0.0780142
VIPS-INFO: 10:21:40.869: shrinkv by 6
VIPS-INFO: 10:21:40.869: shrinkv sequential line cache
VIPS-INFO: 10:21:40.869: reducev: 13 point mask
VIPS-INFO: 10:21:40.869: reducev sequential line cache
VIPS-INFO: 10:21:40.869: residual reduceh by 0.0780142
VIPS-INFO: 10:21:40.869: shrinkh by 6
VIPS-INFO: 10:21:40.869: reduceh: 13 point mask
VIPS-INFO: 10:21:40.870: unpremultiplying alpha
VIPS-INFO: 10:21:40.870: converting to output space srgb
VIPS-INFO: 10:21:40.870: thumbnailing coverimage.jxl as ./coverimage-vipsthumbnail-100x33.jxl

vipsthumbnail 100x

VIPS-INFO: 10:21:40.989: VIPSHOME = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:40.989: VIPS_PREFIX = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:40.989: VIPS_LIBDIR = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:40.989: prefix = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:40.989: libdir = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:40.990: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13"
VIPS-INFO: 10:21:40.990: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-jxl.so"
VIPS-INFO: 10:21:40.993: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-poppler.so"
VIPS-INFO: 10:21:41.001: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-heif.so"
VIPS-INFO: 10:21:41.014: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-openslide.so"
VIPS-INFO: 10:21:41.022: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-magick.so"
VIPS-INFO: 10:21:41.026: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-plugins-8.13"
VIPS-INFO: 10:21:41.031: thumbnailing coverimage.jxl
VIPS-INFO: 10:21:41.052: selected loader is VipsForeignLoadJxlFile
VIPS-INFO: 10:21:41.052: input size is 1273 x 423
VIPS-INFO: 10:21:41.052: loading with factor 1 pre-shrink
VIPS-INFO: 10:21:41.053: pre-shrunk size is 1273 x 423
VIPS-INFO: 10:21:41.053: converting to processing space srgb
VIPS-INFO: 10:21:41.053: premultiplying alpha
VIPS-INFO: 10:21:41.053: residual reducev by 0.0785546
VIPS-INFO: 10:21:41.053: shrinkv by 6
VIPS-INFO: 10:21:41.053: shrinkv sequential line cache
VIPS-INFO: 10:21:41.053: reducev: 13 point mask
VIPS-INFO: 10:21:41.053: reducev sequential line cache
VIPS-INFO: 10:21:41.054: residual reduceh by 0.0785546
VIPS-INFO: 10:21:41.054: shrinkh by 6
VIPS-INFO: 10:21:41.054: reduceh: 13 point mask
VIPS-INFO: 10:21:41.054: unpremultiplying alpha
VIPS-INFO: 10:21:41.054: converting to output space srgb
VIPS-INFO: 10:21:41.054: thumbnailing coverimage.jxl as ./coverimage-vipsthumbnail-100x.jxl

libvips ruby 100x33

VIPS-INFO: 10:21:41.136: selected loader is image source
VIPS-INFO: 10:21:41.136: input size is 1273 x 423
VIPS-INFO: 10:21:41.136: loading with factor 1 pre-shrink
VIPS-INFO: 10:21:41.136: pre-shrunk size is 1273 x 423
VIPS-INFO: 10:21:41.136: converting to processing space srgb
VIPS-INFO: 10:21:41.136: premultiplying alpha
VIPS-INFO: 10:21:41.137: residual reducev by 0.0780142
VIPS-INFO: 10:21:41.137: shrinkv by 6
VIPS-INFO: 10:21:41.137: reducev: 13 point mask
VIPS-INFO: 10:21:41.137: residual reduceh by 0.0780142
VIPS-INFO: 10:21:41.137: shrinkh by 6
VIPS-INFO: 10:21:41.137: reduceh: 13 point mask
VIPS-INFO: 10:21:41.137: unpremultiplying alpha
VIPS-INFO: 10:21:41.138: converting to output space srgb

libvips ruby 100x

VIPS-INFO: 10:21:41.238: selected loader is image source
VIPS-INFO: 10:21:41.238: input size is 1273 x 423
VIPS-INFO: 10:21:41.238: loading with factor 1 pre-shrink
VIPS-INFO: 10:21:41.238: pre-shrunk size is 1273 x 423
VIPS-INFO: 10:21:41.238: converting to processing space srgb
VIPS-INFO: 10:21:41.238: premultiplying alpha
VIPS-INFO: 10:21:41.238: residual reducev by 0.0785546
VIPS-INFO: 10:21:41.238: shrinkv by 6
VIPS-INFO: 10:21:41.238: reducev: 13 point mask
VIPS-INFO: 10:21:41.238: residual reduceh by 0.0785546
VIPS-INFO: 10:21:41.238: shrinkh by 6
VIPS-INFO: 10:21:41.238: reduceh: 13 point mask
VIPS-INFO: 10:21:41.239: unpremultiplying alpha
VIPS-INFO: 10:21:41.239: converting to output space srgb

Results

Vipsthumbnail 100x33: 99x33

Libvipsrb 100x33: 99x33

Vipsthumbnail 100x: 100x33

Libvipsrb 100x: 100x33

coverimage.png

vipsthumbnail 100x33

VIPS-INFO: 10:21:41.351: VIPSHOME = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:41.351: VIPS_PREFIX = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:41.351: VIPS_LIBDIR = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:41.351: prefix = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:41.351: libdir = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:41.352: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13"
VIPS-INFO: 10:21:41.352: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-jxl.so"
VIPS-INFO: 10:21:41.354: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-poppler.so"
VIPS-INFO: 10:21:41.360: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-heif.so"
VIPS-INFO: 10:21:41.373: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-openslide.so"
VIPS-INFO: 10:21:41.377: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-magick.so"
VIPS-INFO: 10:21:41.380: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-plugins-8.13"
VIPS-INFO: 10:21:41.386: thumbnailing coverimage.png
VIPS-INFO: 10:21:41.388: selected loader is VipsForeignLoadPngFile
VIPS-INFO: 10:21:41.388: input size is 1273 x 423
VIPS-INFO: 10:21:41.388: loading with factor 1 pre-shrink
VIPS-INFO: 10:21:41.388: pre-shrunk size is 1273 x 423
VIPS-INFO: 10:21:41.388: converting to processing space srgb
VIPS-INFO: 10:21:41.388: premultiplying alpha
VIPS-INFO: 10:21:41.389: residual reducev by 0.0780142
VIPS-INFO: 10:21:41.389: shrinkv by 6
VIPS-INFO: 10:21:41.389: shrinkv sequential line cache
VIPS-INFO: 10:21:41.389: reducev: 13 point mask
VIPS-INFO: 10:21:41.389: reducev sequential line cache
VIPS-INFO: 10:21:41.389: residual reduceh by 0.0780142
VIPS-INFO: 10:21:41.389: shrinkh by 6
VIPS-INFO: 10:21:41.389: reduceh: 13 point mask
VIPS-INFO: 10:21:41.390: unpremultiplying alpha
VIPS-INFO: 10:21:41.390: converting to output space srgb
VIPS-INFO: 10:21:41.390: thumbnailing coverimage.png as ./coverimage-vipsthumbnail-100x33.png

vipsthumbnail 100x

VIPS-INFO: 10:21:41.468: VIPSHOME = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:41.469: VIPS_PREFIX = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:41.469: VIPS_LIBDIR = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:41.469: prefix = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:41.469: libdir = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:41.470: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13"
VIPS-INFO: 10:21:41.470: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-jxl.so"
VIPS-INFO: 10:21:41.472: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-poppler.so"
VIPS-INFO: 10:21:41.478: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-heif.so"
VIPS-INFO: 10:21:41.489: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-openslide.so"
VIPS-INFO: 10:21:41.493: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-magick.so"
VIPS-INFO: 10:21:41.496: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-plugins-8.13"
VIPS-INFO: 10:21:41.501: thumbnailing coverimage.png
VIPS-INFO: 10:21:41.502: selected loader is VipsForeignLoadPngFile
VIPS-INFO: 10:21:41.502: input size is 1273 x 423
VIPS-INFO: 10:21:41.502: loading with factor 1 pre-shrink
VIPS-INFO: 10:21:41.502: pre-shrunk size is 1273 x 423
VIPS-INFO: 10:21:41.502: converting to processing space srgb
VIPS-INFO: 10:21:41.502: premultiplying alpha
VIPS-INFO: 10:21:41.502: residual reducev by 0.0785546
VIPS-INFO: 10:21:41.502: shrinkv by 6
VIPS-INFO: 10:21:41.502: shrinkv sequential line cache
VIPS-INFO: 10:21:41.502: reducev: 13 point mask
VIPS-INFO: 10:21:41.502: reducev sequential line cache
VIPS-INFO: 10:21:41.503: residual reduceh by 0.0785546
VIPS-INFO: 10:21:41.503: shrinkh by 6
VIPS-INFO: 10:21:41.503: reduceh: 13 point mask
VIPS-INFO: 10:21:41.503: unpremultiplying alpha
VIPS-INFO: 10:21:41.503: converting to output space srgb
VIPS-INFO: 10:21:41.503: thumbnailing coverimage.png as ./coverimage-vipsthumbnail-100x.png

libvips ruby 100x33

VIPS-INFO: 10:21:41.536: selected loader is image source
VIPS-INFO: 10:21:41.536: input size is 1273 x 423
VIPS-INFO: 10:21:41.536: loading with factor 1 pre-shrink
VIPS-INFO: 10:21:41.536: pre-shrunk size is 1273 x 423
VIPS-INFO: 10:21:41.536: converting to processing space srgb
VIPS-INFO: 10:21:41.536: premultiplying alpha
VIPS-INFO: 10:21:41.536: residual reducev by 0.0780142
VIPS-INFO: 10:21:41.536: shrinkv by 6
VIPS-INFO: 10:21:41.536: shrinkv sequential line cache
VIPS-INFO: 10:21:41.536: reducev: 13 point mask
VIPS-INFO: 10:21:41.537: reducev sequential line cache
VIPS-INFO: 10:21:41.537: residual reduceh by 0.0780142
VIPS-INFO: 10:21:41.537: shrinkh by 6
VIPS-INFO: 10:21:41.537: reduceh: 13 point mask
VIPS-INFO: 10:21:41.538: unpremultiplying alpha
VIPS-INFO: 10:21:41.539: converting to output space srgb

libvips ruby 100x

VIPS-INFO: 10:21:41.580: selected loader is image source
VIPS-INFO: 10:21:41.580: input size is 1273 x 423
VIPS-INFO: 10:21:41.580: loading with factor 1 pre-shrink
VIPS-INFO: 10:21:41.580: pre-shrunk size is 1273 x 423
VIPS-INFO: 10:21:41.580: converting to processing space srgb
VIPS-INFO: 10:21:41.580: premultiplying alpha
VIPS-INFO: 10:21:41.580: residual reducev by 0.0785546
VIPS-INFO: 10:21:41.580: shrinkv by 6
VIPS-INFO: 10:21:41.580: shrinkv sequential line cache
VIPS-INFO: 10:21:41.580: reducev: 13 point mask
VIPS-INFO: 10:21:41.580: reducev sequential line cache
VIPS-INFO: 10:21:41.581: residual reduceh by 0.0785546
VIPS-INFO: 10:21:41.581: shrinkh by 6
VIPS-INFO: 10:21:41.581: reduceh: 13 point mask
VIPS-INFO: 10:21:41.582: unpremultiplying alpha
VIPS-INFO: 10:21:41.582: converting to output space srgb

Results

Vipsthumbnail 100x33: 99x33

Libvipsrb 100x33: 99x33

Vipsthumbnail 100x: 100x33

Libvipsrb 100x: 100x33

coverimage.tiff

vipsthumbnail 100x33

VIPS-INFO: 10:21:41.672: VIPSHOME = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:41.673: VIPS_PREFIX = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:41.673: VIPS_LIBDIR = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:41.673: prefix = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:41.673: libdir = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:41.674: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13"
VIPS-INFO: 10:21:41.674: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-jxl.so"
VIPS-INFO: 10:21:41.676: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-poppler.so"
VIPS-INFO: 10:21:41.681: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-heif.so"
VIPS-INFO: 10:21:41.692: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-openslide.so"
VIPS-INFO: 10:21:41.696: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-magick.so"
VIPS-INFO: 10:21:41.699: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-plugins-8.13"
VIPS-INFO: 10:21:41.704: thumbnailing coverimage.tiff
VIPS-INFO: 10:21:41.712: selected loader is VipsForeignLoadTiffFile
VIPS-INFO: 10:21:41.712: input size is 1273 x 423
VIPS-INFO: 10:21:41.712: loading with factor 1 pre-shrink
VIPS-INFO: 10:21:41.713: pre-shrunk size is 1273 x 423
VIPS-INFO: 10:21:41.713: converting to processing space srgb
VIPS-INFO: 10:21:41.713: premultiplying alpha
VIPS-INFO: 10:21:41.713: residual reducev by 0.0780142
VIPS-INFO: 10:21:41.713: shrinkv by 6
VIPS-INFO: 10:21:41.714: shrinkv sequential line cache
VIPS-INFO: 10:21:41.714: reducev: 13 point mask
VIPS-INFO: 10:21:41.714: reducev sequential line cache
VIPS-INFO: 10:21:41.714: residual reduceh by 0.0780142
VIPS-INFO: 10:21:41.714: shrinkh by 6
VIPS-INFO: 10:21:41.714: reduceh: 13 point mask
VIPS-INFO: 10:21:41.714: unpremultiplying alpha
VIPS-INFO: 10:21:41.714: converting to output space srgb
VIPS-INFO: 10:21:41.714: thumbnailing coverimage.tiff as ./coverimage-vipsthumbnail-100x33.tiff

vipsthumbnail 100x

VIPS-INFO: 10:21:41.802: VIPSHOME = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:41.803: VIPS_PREFIX = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:41.803: VIPS_LIBDIR = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:41.803: prefix = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:41.803: libdir = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:41.804: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13"
VIPS-INFO: 10:21:41.804: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-jxl.so"
VIPS-INFO: 10:21:41.806: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-poppler.so"
VIPS-INFO: 10:21:41.813: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-heif.so"
VIPS-INFO: 10:21:41.827: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-openslide.so"
VIPS-INFO: 10:21:41.831: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-magick.so"
VIPS-INFO: 10:21:41.834: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-plugins-8.13"
VIPS-INFO: 10:21:41.841: thumbnailing coverimage.tiff
VIPS-INFO: 10:21:41.845: selected loader is VipsForeignLoadTiffFile
VIPS-INFO: 10:21:41.845: input size is 1273 x 423
VIPS-INFO: 10:21:41.845: loading with factor 1 pre-shrink
VIPS-INFO: 10:21:41.846: pre-shrunk size is 1273 x 423
VIPS-INFO: 10:21:41.846: converting to processing space srgb
VIPS-INFO: 10:21:41.846: premultiplying alpha
VIPS-INFO: 10:21:41.846: residual reducev by 0.0785546
VIPS-INFO: 10:21:41.846: shrinkv by 6
VIPS-INFO: 10:21:41.847: shrinkv sequential line cache
VIPS-INFO: 10:21:41.847: reducev: 13 point mask
VIPS-INFO: 10:21:41.847: reducev sequential line cache
VIPS-INFO: 10:21:41.847: residual reduceh by 0.0785546
VIPS-INFO: 10:21:41.847: shrinkh by 6
VIPS-INFO: 10:21:41.847: reduceh: 13 point mask
VIPS-INFO: 10:21:41.847: unpremultiplying alpha
VIPS-INFO: 10:21:41.847: converting to output space srgb
VIPS-INFO: 10:21:41.847: thumbnailing coverimage.tiff as ./coverimage-vipsthumbnail-100x.tiff

libvips ruby 100x33

VIPS-INFO: 10:21:41.891: selected loader is image source
VIPS-INFO: 10:21:41.891: input size is 1273 x 423
VIPS-INFO: 10:21:41.891: loading with factor 1 pre-shrink
VIPS-INFO: 10:21:41.891: pre-shrunk size is 1273 x 423
VIPS-INFO: 10:21:41.891: converting to processing space srgb
VIPS-INFO: 10:21:41.891: premultiplying alpha
VIPS-INFO: 10:21:41.891: residual reducev by 0.0780142
VIPS-INFO: 10:21:41.891: shrinkv by 6
VIPS-INFO: 10:21:41.892: shrinkv sequential line cache
VIPS-INFO: 10:21:41.892: reducev: 13 point mask
VIPS-INFO: 10:21:41.892: reducev sequential line cache
VIPS-INFO: 10:21:41.893: residual reduceh by 0.0780142
VIPS-INFO: 10:21:41.893: shrinkh by 6
VIPS-INFO: 10:21:41.893: reduceh: 13 point mask
VIPS-INFO: 10:21:41.894: unpremultiplying alpha
VIPS-INFO: 10:21:41.894: converting to output space srgb

libvips ruby 100x

VIPS-INFO: 10:21:41.936: selected loader is image source
VIPS-INFO: 10:21:41.936: input size is 1273 x 423
VIPS-INFO: 10:21:41.936: loading with factor 1 pre-shrink
VIPS-INFO: 10:21:41.936: pre-shrunk size is 1273 x 423
VIPS-INFO: 10:21:41.936: converting to processing space srgb
VIPS-INFO: 10:21:41.936: premultiplying alpha
VIPS-INFO: 10:21:41.936: residual reducev by 0.0785546
VIPS-INFO: 10:21:41.936: shrinkv by 6
VIPS-INFO: 10:21:41.936: shrinkv sequential line cache
VIPS-INFO: 10:21:41.937: reducev: 13 point mask
VIPS-INFO: 10:21:41.937: reducev sequential line cache
VIPS-INFO: 10:21:41.937: residual reduceh by 0.0785546
VIPS-INFO: 10:21:41.937: shrinkh by 6
VIPS-INFO: 10:21:41.938: reduceh: 13 point mask
VIPS-INFO: 10:21:41.938: unpremultiplying alpha
VIPS-INFO: 10:21:41.938: converting to output space srgb

Results

Vipsthumbnail 100x33: 99x33

Libvipsrb 100x33: 99x33

Vipsthumbnail 100x: 100x33

Libvipsrb 100x: 100x33

coverimage.webp

vipsthumbnail 100x33

VIPS-INFO: 10:21:42.035: VIPSHOME = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:42.036: VIPS_PREFIX = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:42.036: VIPS_LIBDIR = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:42.036: prefix = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:42.036: libdir = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:42.037: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13"
VIPS-INFO: 10:21:42.037: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-jxl.so"
VIPS-INFO: 10:21:42.039: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-poppler.so"
VIPS-INFO: 10:21:42.047: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-heif.so"
VIPS-INFO: 10:21:42.063: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-openslide.so"
VIPS-INFO: 10:21:42.067: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-magick.so"
VIPS-INFO: 10:21:42.070: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-plugins-8.13"
VIPS-INFO: 10:21:42.075: thumbnailing coverimage.webp
VIPS-INFO: 10:21:42.077: selected loader is VipsForeignLoadWebpFile
VIPS-INFO: 10:21:42.077: input size is 1273 x 423
VIPS-INFO: 10:21:42.077: loading with factor 12.8182 pre-shrink
VIPS-INFO: 10:21:42.077: pre-shrunk size is 99 x 33
VIPS-INFO: 10:21:42.077: converting to processing space srgb
VIPS-INFO: 10:21:42.078: converting to output space srgb
VIPS-INFO: 10:21:42.078: thumbnailing coverimage.webp as ./coverimage-vipsthumbnail-100x33.webp

vipsthumbnail 100x

VIPS-INFO: 10:21:42.138: VIPSHOME = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:42.138: VIPS_PREFIX = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:42.138: VIPS_LIBDIR = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:42.138: prefix = /usr/local/Cellar/vips/8.13.0
VIPS-INFO: 10:21:42.138: libdir = /usr/local/Cellar/vips/8.13.0/lib
VIPS-INFO: 10:21:42.140: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13"
VIPS-INFO: 10:21:42.140: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-jxl.so"
VIPS-INFO: 10:21:42.142: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-poppler.so"
VIPS-INFO: 10:21:42.147: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-heif.so"
VIPS-INFO: 10:21:42.158: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-openslide.so"
VIPS-INFO: 10:21:42.162: loading "/usr/local/Cellar/vips/8.13.0/lib/vips-modules-8.13/vips-magick.so"
VIPS-INFO: 10:21:42.165: searching "/usr/local/Cellar/vips/8.13.0/lib/vips-plugins-8.13"
VIPS-INFO: 10:21:42.170: thumbnailing coverimage.webp
VIPS-INFO: 10:21:42.170: selected loader is VipsForeignLoadWebpFile
VIPS-INFO: 10:21:42.170: input size is 1273 x 423
VIPS-INFO: 10:21:42.170: loading with factor 12.73 pre-shrink
VIPS-INFO: 10:21:42.171: pre-shrunk size is 100 x 33
VIPS-INFO: 10:21:42.171: converting to processing space srgb
VIPS-INFO: 10:21:42.171: converting to output space srgb
VIPS-INFO: 10:21:42.171: thumbnailing coverimage.webp as ./coverimage-vipsthumbnail-100x.webp

libvips ruby 100x33

VIPS-INFO: 10:21:42.187: selected loader is image source
VIPS-INFO: 10:21:42.187: input size is 1273 x 423
VIPS-INFO: 10:21:42.187: loading with factor 1 pre-shrink
VIPS-INFO: 10:21:42.187: pre-shrunk size is 1273 x 423
VIPS-INFO: 10:21:42.187: converting to processing space srgb
VIPS-INFO: 10:21:42.188: residual reducev by 0.0780142
VIPS-INFO: 10:21:42.188: shrinkv by 6
VIPS-INFO: 10:21:42.188: reducev: 13 point mask
VIPS-INFO: 10:21:42.188: residual reduceh by 0.0780142
VIPS-INFO: 10:21:42.188: shrinkh by 6
VIPS-INFO: 10:21:42.188: reduceh: 13 point mask
VIPS-INFO: 10:21:42.188: converting to output space srgb

libvips ruby 100x

VIPS-INFO: 10:21:42.233: selected loader is image source
VIPS-INFO: 10:21:42.233: input size is 1273 x 423
VIPS-INFO: 10:21:42.233: loading with factor 1 pre-shrink
VIPS-INFO: 10:21:42.233: pre-shrunk size is 1273 x 423
VIPS-INFO: 10:21:42.234: converting to processing space srgb
VIPS-INFO: 10:21:42.234: residual reducev by 0.0785546
VIPS-INFO: 10:21:42.234: shrinkv by 6
VIPS-INFO: 10:21:42.234: reducev: 13 point mask
VIPS-INFO: 10:21:42.234: residual reduceh by 0.0785546
VIPS-INFO: 10:21:42.234: shrinkh by 6
VIPS-INFO: 10:21:42.234: reduceh: 13 point mask
VIPS-INFO: 10:21:42.235: converting to output space srgb

Results

Vipsthumbnail 100x33: 99x33

Libvipsrb 100x33: 99x33

Vipsthumbnail 100x: 100x33

Libvipsrb 100x: 100x33

[jcupitt]

Hi, I'll have a look.

I expect you saw you can use --force to make it break aspect ratio. It might fix your immediate problem.

[jcupitt]

I think this is down to differences in shrink on load behaviour between the file format libraries.

Your ruby code is using thumbnail_image, which does not use any shrink on load tricks (and can be very slow as a result). libjpeg shrink-on-load always rounds down, but libwebp shrink on load does round to nearest.

I'm not sure what we could do to make it more consistent. We use libwebp shrink-on-load for the whole shrink at the moment. Perhaps we should leave the final 200% to libvips? I expect you could still find corner cases where dimensions were different though.

I suppose thumbnail could also do a non-rectangular final stage to ensure we always hit consistent dimensions, but that would mean slightly non-rectangular pixels, which I would hate.