Package: pelican-image-process
Image Process: A Plugin for PelicanImage Processis a plugin forPelican,
a static site generator written in Python.Image Processlet you automate the processing of images based on their
class attribute. Use this plugin to minimize the overall page weight
and to save you a trip to Gimp or Photoshop each time you include an
image in your post.Image Processalso makes it easy to create responsive images using
the HTML5srcsetattribute and<picture>tag. It does this
by generating multiple derivative images from one or more sources.Image Processwill not overwrite your original images.InstallationThe easiest way to installImage Processis via Pip. This
will also install the required dependencies automatically.python-mpipinstallpelican-image-processYou will then need to configure your desired transformations (seeUsagebelow) and add the appropriate class to images you want processed.UsageImage Processscans your content for<img>tags with special
classes. It then maps the classes to a set of image processing
instructions, computes new images, and modifies HTML code according to
the instructions.Define TransformationsThe first step in using this module is to define some image
transformations in your Pelican configuration file. Transformations
are defined in theIMAGE_PROCESSdictionary, mapping a
transformation name to a list of operations. There are three kinds of
transformations: image replacement, responsive image, and picture set.Image ReplacementThe simplest image processing will replace the original image by a
new, transformed image computed from the original. You may use this,
for example, to ensure that all images are of the same size, or to
compute a thumbnail from a larger image:IMAGE_PROCESS={"article-image":["scale_in 300 300 True"],"thumb":["crop 0 0 50% 50%","scale_out 150 150 True","crop 0 0 150 150"],}These transformations tellImage Processto transform the image
referred to by thesrcattribute of an<img>according to the
list of operations specified, and replace thesrcattribute with the
URL of the transformed image.For consistency with other types of transformations described
below, there is an alternative syntax for the processing instructions:IMAGE_PROCESS={"thumb":{"type":"image","ops":["crop 0 0 50% 50%","scale_out 150 150 True","crop 0 0 150 150"],},"article-image":{"type":"image","ops":["scale_in 300 300 True"],},}To apply image replacement to the images in your articles, you must add to them
the special classimage-process-<transform>, in which<transform>is the ID
of the transformation you wish to apply.Let's say you have defined the transformation described above. To get your
image processed, it needs to have the right CSS class:<imgclass="image-process-article-image"src="/images/pelican.jpg"/>This can be produced in Markdown with:![](/images/pelican.png){: .image-process-article-image}In reStructuredText, use the:class:attribute of theimageor
thefiguredirective:..image::/images/pelican.png:class:image-process-article-image..figure::/images/pelican.png:class:image-process-article-image⚠️Warning:The reStructuredText reader will convert underscores (_) to
dashes (-) in class names. To make sure everything runs
smoothly, do not use underscores in your transformation names.Responsive ImagesYou can useImage Processto automatically generate a set of
images that will be selected for display by browsers according to the
viewport width or according to the device resolution. To accomplish
this,Image Processwill add asrcsetattribute(and maybe amediaand asizesattribute) to the<img>tag.HTML5 supports two types of responsive image sets. The first one is
device-pixel-ratio-based, selecting higher resolution images for higher
resolution devices; the second one is viewport-based, selecting
images according to the viewport size. You can read more aboutHTML5 responsive imagesfor a gentle introduction to thesrcsetand<picture>syntaxes.To tellImage Processto generate a responsive image, add aresponsive-imagetransformation to your yourIMAGE_PROCESSdictionary, with the following syntax:IMAGE_PROCESS={"crisp":{"type":"responsive-image","srcset":[("1x",["scale_in 800 600 True"]),("2x",["scale_in 1600 1200 True"]),("4x",["scale_in 3200 2400 True"]),],"default":"1x",},"large-photo":{"type":"responsive-image","sizes":("(min-width: 1200px) 800px, ""(min-width: 992px) 650px, ""(min-width: 768px) 718px, ""100vw"),"srcset":[("600w",["scale_in 600 450 True"]),("800w",["scale_in 800 600 True"]),("1600w",["scale_in 1600 1200 True"]),],"default":"800w",},}Thecrisptransformation is an example of a transformation
enabling device-pixel-ratio-based selection. Thesrcsetis a list
of tuples, each tuple containing the image description ("1x","2x", etc.) and the list of operations to generate the derivative
image from the original image (the original image is the value of thesrcattribute of the<img>). Image descriptions are hints
about the resolution of the associated image and must have the suffixx. Thedefaultsetting specifies the image to use to replace thesrcattribute of the image.  This is the image that will be displayed by
browsers that do not support thesrcsetsyntax.Thelarge-phototransformation is an example of a transformation
enabling viewport-based selection. Thesizescontains a rule to
compute the width of the displayed image from the width of the
viewport. Once the browser knows the image width, it will select an
image source from thesrcset. Thesrcsetis a list of tuple,
each tuple containing the image description ("600w","800w",
etc.) and the list of operations to generate the derivative image from
the original image (the original image is the value of thesrcattribute of the<img>). Image descriptions are hints about the
width in pixels of the associated image and must have the suffixw. Thedefaultsetting specifies the image to use to replace thesrcattribute of the image.  This is the image that will be displayed by
browsers that do not support thesrcsetsyntax.In the two examples above, thedefaultsetting is a string referring to
one of the images in thesrcset. However, thedefaultvalue
could also be a list of operations to generate a different derivative
image.To make the images in your article responsive, you must add to them the
special classimage-process-<transform>, in which<transform>is the ID of the
transformation you wish to apply, exactly like you would do for the
image replacement case, described above.So, in HTML it should look like this:<imgclass="image-process-large-photo"src="/images/pelican.jpg"/>Which can be produced in Markdown with:![](/images/pelican.jpg){: .image-process-large-photo}In reStructuredText, use the:class:attribute of theimageor
thefiguredirective:..image::/images/pelican.jpg:class:image-process-large-photo..figure::/images/pelican.jpg:class:image-process-large-photoPicture SetImage Processcan be used to generate the images used by a<picture>tag. The<picture>syntax allows for more
flexibility in providing a choice of image to the browser.
Again, you can read more aboutHTML5 responsive imagesfor a
gentle introduction to thesrcsetand<picture>syntaxes.To tellImage Processto generate the images for a<picture>,
add apictureentry to yourIMAGE_PROCESSdictionary with the
following syntax:IMAGE_PROCESS={"example-pict":{"type":"picture","sources":[{"name":"default","media":"(min-width: 640px)","srcset":[("640w",["scale_in 640 480 True"]),("1024w",["scale_in 1024 683 True"]),("1600w",["scale_in 1600 1200 True"]),],"sizes":"100vw",},{"name":"source-1","srcset":[("1x",["crop 100 100 200 200"]),("2x",["crop 100 100 300 300"]),]},],"default":("default","640w"),},}Each of thesourcesentries is very similar to theresponsive imagedescribe above. Here, each source must have aname, which
will be used to find the URL of the original image for this source in
your article. The source may also have amedia, which contains a
rule used by the browser to select the active source. Thedefaultsetting specifies the image to use to replace thesrcattribute of
the<img>inside the<picture>.  This is the image that will be
displayed by browsers that do not support the<picture>syntax. In
this example, it will use the image640wfrom the sourcedefault.
A list of operations could have been specified instead of640w.To generate a responsive<picture>for the images in your
articles, you must add to your article a pseudo<picture>tag that
looks like this:<picture><sourceclass="source-1"src="/images/pelican-closeup.jpg"></source><imgclass="image-process-example-pict"src="/images/pelican.jpg"/></picture>Each<source>tag maps a source name (theclassattribute) to
a file (thesrcattribute). The<img>must have the special
classimage-process-followed by the name of the transformation
you wish to apply. The file referenced by thesrcattribute of the<img>will be used as the specialdefaultsource in your
transformation definition.You can't produce this with pure Markdown and must instead resort to raw HTML.In reStructuredText, however, you can also use thefiguredirective
to generate a<picture>. The figure image file will be used as the
specialdefaultsource; other sources must be added in the legend
section of thefigureasimagedirectives. The figure class must
beimage-process-followed by the name of the transformation you
wish to apply, while the other images must have two classes:image-processand the name of the source they provide an image for:..figure::/images/pelican.jpg:class:image-process-example-pict

    Test picture..image::/images/pelican-closeup.jpg:class:image-process source-1The images in the legend section that are used as source for the<picture>will be removed from the image legend, so that they do
not appear in your final article.TransformationsAvailable operations for transformations are:crop <top> <left> <right> <bottom>:Crop the image to the box (<left>,<top>)-(<right>,<bottom>). Values
can be absolute (a number) or relative to the size of the image (a
number followed by a percent sign%).flip_horizontal:Flip the image horizontally.flip_vertical:Flip the image vertically.grayscale:Convert the image to grayscale.resize <width> <height>:Resize the image. This operation doesnotpreserve the image aspect
ratio. Values can be absolute (a number) or relative to the
size of the image (a number followed by a percent sign%).rotate <degrees>:Rotate the image.scale_in <width> <height> <upscale>:Resize the image. This operation preserves the image aspect ratio
and the resulting image will be no larger than<width>x<height>. Values can be absolute (a number) or relative to the
size of the image (a number followed by a percent sign%).
If<upscale>isFalse, smaller images will not be enlarged.scale_out <width> <height> <upscale>:Resize the image. This operation preserves the image aspect ratio
and the resulting image will be no smaller than<width>x<height>. Values can be absolute (a number) or relative to the
size of the image (a number followed by a percent sign%).
If<upscale>isFalse, smaller images will not be enlarged.blur:Apply thepillow.ImageFilter.BLURfilter to the image.contour:Apply thepillow.ImageFilter.CONTOURfilter to the image.detail:Apply thepillow.ImageFilter.DETAILfilter to the image.edge_enhance:Apply thepillow.ImageFilter.EDGE_ENHANCEfilter to the image.edge_enhance_more:Apply thepillow.ImageFilter.EDGE_ENHANCE_MOREfilter to the image.emboss:Apply thepillow.ImageFilter.EMBOSSfilter to the image.find_edges:Apply thepillow.ImageFilter.FIND_EDGESfilter to the image.smooth:Apply thepillow.ImageFilter.SMOOTH filterto the image.smooth_more:Apply thepillow.ImageFilter.SMOOTH_MOREfilter to the image.sharpen:Apply thepillow.ImageFilter.SHARPENfilter to the image.You can also define your own operations; the only requirement is that
your operation should be a callable object expecting apillow.Imageas
its first parameter and it should return the transformed image:defcrop_face(image):"""Detect face in image and crop around it."""# Fancy algorithm.returnimageIMAGE_PROCESS={"face-thumbnail":[crop_face,"scale_out 150 150 True"]}Additional SettingsDestination DirectoryBy default, the new images will be stored in a directory namedderivative/<TRANSFORMATION_NAME>in the output folder at
the same location as the original image.
For example, if the original image is located in
thecontent/imagesfolder, the computed images will be stored
inoutput/images/derivative/<TRANSFORMATION_NAME>.
All the transformations are done in the output directory in order
to avoid confusion with the source files or if we test multiple
transformations. You can replacederivativeby something else using
theIMAGE_PROCESS_DIRsetting in your Pelican settings file:IMAGE_PROCESS_DIR="derivees"Force Image ProcessingIf the transformed image already exists and is newer than the original
image, the plugin assumes that it should not re-compute it again. You
can force the plugin to re-compute all images by settingIMAGE_PROCESS_FORCEtoTruein your Pelican configuration file.IMAGE_PROCESS_FORCE=TrueSelecting a HTML ParserYou may select the HTML parser which is used. The default is the built-inhtml.parserbut you may also selecthtml5liborlxmlby settingIMAGE_PROCESS_PARSERin your Pelican settings file. For example:IMAGE_PROCESS_PARSER="html5lib"For details, refer to theBeautifulSoup documentation on parsers.File EncodingYou may select a different file encoding to be used by BeautifulSoup as it
opens your files. The default isutf-8.IMAGE_PROCESS_ENCODING="utf-8"Copying EXIF TagsYou may askImage Processto copy the EXIF tags from your original image to
the transformed images. You must haveexiftoolinstalled.IMAGE_PROCESS_COPY_EXIF_TAGS=TrueKnown IssuesPillow, when resizing animated GIF files,does not return an animated file.ContributingContributions are welcome and much appreciated. Every little bit helps. You can contribute by improving the documentation, adding missing features, and fixing bugs. You can also help out by reviewing and commenting onexisting issues.To start contributing to this plugin, review theContributing to Pelicandocumentation, beginning with theContributing Codesection.Regenerating Test ImagesIf you need to regenerate the transformed images used by the test suite, there
is a helper function to do this for you. From the Python REPL:>>>frompelican.plugins.image_process.test_image_processimportgenerate_test_images>>>generate_test_images()36 test images generated!LicenseThis project is licensed under theAGPL-3.0 license.Pelican imagein test data by Jon Sullivan. Published under aCreative Commons Public Domain license.