plone.scale 3.1.0

Image scaling

Introduction

This package contains image scaling logic for use in Zope environments. It supports Zope 2, grok and other systems build on using the Zope ToolKit (ZTK).

Several design goals were used when writing this package:

• image scaling to any width, height, width&height should be supported using both up-scaling and down-scaling. Scaling parameters should never be fixed in code. This allows designers to use any image scale they want without having to modify python code.

• the result of scaling will be an image along with its new size, not a HTML or XHTML tag. We already have excellent tools to generate tags in the form of Zope Pagetemplates, Genshi and other template languages that are much better suited for this purpose.

In addition several implementation goals were defined:

• image scaling must happen on demand instead of up-front. This reduces initial save time and prevents unnecessary scalings from being generated.

• image scaling parameters should not be part of the generated URL. Since the number of parameters can change and new parameters may be added in the future this would create overly complex URLs and URL parsing.

• no HTML rewriting (such as done by repoze.bitblt) should be required.

• it should be possibly to develop an external storage system which stores scaled images externally and returns a URL which bypasses the application server. This should be configurable via just a filesystem path & base URL.

• minimum number of external dependencies, allowing this package to be used in many environments.

• testable without requiring zope.testing. Running setup.py test should be sufficient.

• URLs for scaled images should have an extension which reflects their MIME type. This is facilitates cache (and other front-end services) configuration.

Usage

The most common way to use plone.scale is from a HTML template. In TAL syntax a typical usage looks like this:

<img tal:define="scales context/@@image-scaling;
                 thumbnail python:scales.scale('logo', width=64, height=64)"
     tal:attributes="src thumbnail/url;
                     width thumbnail/width;
                     height thumbnail/height" />

This generates a thumbnail of an image field called logo with a maximum size of 64x64 pixels. The dimensions of the resulting image (which might not be exactly 64x64) are set as attributes on the img tag to speed up browser rendering.

If you prefer Genshi syntax and have the IImageScaleStorage interface in scope the syntax looks like this:

<img py:with="thumbnail=IImageScaleStorage(context).scale('logo', width=64, heigh=64)"
     py:attributes="dict(src=thumbnail.url, width=thumbnail.width, height=thumbnail.height" />

Changelog

3.1.0 (2020-03-08)

New features:

• The mode argument replaces the old, now deprecated, direction argument. The new names are contain or scale-crop-to-fit instead of down, cover or scale-crop-to-fill instead of up and scale instead of thumbnail. [fschulze] (#29)

• Added calculate_scaled_dimensions function to calculate sizes from bare values without actually scaling an image. [fschulze]

  Added MAX_PIXELS constant set to 8192*8192 to prevent memory overflow while scaling. [fschulze] (#37)

Bug fixes:

• Fix documentation of scaling modes to match it’s behavior. [thet] (#39)

3.0.3 (2018-11-04)

Bug fixes:

• reduce warnings in tests [jensens]

3.0.2 (2018-09-28)

Bug fixes:

• Fix cleanup of image scales in py3 [pbauer]

3.0.1 (2018-04-03)

Bug fixes:

• Fix conflict resolution code corner case. [gforcada]

3.0 (2017-10-02)

Breaking changes:

• Restore scale down behaviour from 1.x series without the huge memory usage. [fschulze]

New features:

• Handle TIFF images with alpha channels. [fschulze]

2.2 (2017-08-27)

New features:

• Python 3 compatibility. [dhavlik]

2.1.2 (2017-05-31)

Bug fixes:

• Remove unused dependency. [gforcada]

2.1.1 (2017-03-29)

Bug fixes:

• Only convert JPEG to greyscale if they actually are and not when the image has less than 256 colors. This bug was introduced in 2.1 with PR #13. [fschulze]

• Preserve color profile in scaled images. [fschulze]

2.1 (2016-11-01)

New features:

• Choose an appropriate image mode in order to reduce file size. [didrix]

Bug fixes:

• Require the six package so we can more easily check number types. On Python 3 long has been merged into int. [maurits]

• When getting an outdated scale, don’t throw it away when there is no factory. [maurits]

• Avoid TypeErrors when looking for outdated scales. Fixes issue 12. [maurits]

• Catch KeyError when deleting non existing scale. This can happen in corner cases. Fixes issue 15. [maurits]

• Set zip_safe=False in setup.py. Otherwise you cannot run the tests of the released package because the test runner does not find any tests in the egg file. Note that this is only a problem in zc.buildout 1.x: it uses unzip=False by default. zc.buildout 2.x no longer has this option and always unzips eggs. [maurits]

2.0 (2016-08-12)

New:

• Assume a width or height of zero is semantically the same as None already was: Use the other dimension to scale, calculate the missing one. [jensens, thet]

• Scaled GIFs are converted to RGBA PNG images instead of converting them to JPEG. [thet, jensens]

Fixes:

• Don’t scale images up for direction “down”. [thet]

• Major housekeeping, code refactored in order to reduce complexicty. [jensens]

1.5.0 (2016-05-18)

New:

• Use an adapter to lookup the actual factory for scaling. Deprecated passing the factory as named parameter along, because this had not enough flexibility: If addons want to provide alterative methods to scale (i.e. cropping), now a specific adapter can perform the work. [jensens]

Fixes:

• Minor housekeeping. [jensens]

1.4.1 (2016-02-12)

Fixes:

• Fix KeyError in storage.AnnotationStorage._cleanup when attempting to delete the storage for the same key twice. [fulv]

1.4 (2015-12-07)

New:

• Resolve conflicts raised when accessing multiple scales concurrently. [gotcha]

• Refactored scale storage. [gotcha]

1.3.5 (2015-03-10)

• PIL thumbnail does not work for magnifying images (when scaling up). Use resize instead. [sureshvv]

1.3.4 (2014-09-07)

• When a scale is outdated, discard all image scales that are more than a day older than the context. Refs https://dev.plone.org/ticket/13791 [maurits]

• Make sure deleting items or clearing a complete storage works. Deleting one item would often delete a linked second item, which made it hard to remove several items at once. [maurits]

1.3.3 (2014-01-27)

• Discard old image scales if item was modified. Refs https://dev.plone.org/ticket/13791 [gforcada]

• Generate Progressive JPEG. [kroman0]

1.3.2 (2013-05-23)

• Added a marker interface for scaled image quality. Refs http://dev.plone.org/plone/ticket/13337 [khink]

1.3.1 (2013-04-06)

• Cropped images are now centralised vertically as well as horizontally [mattss]

1.3 (2013-01-17)

• Add MANIFEST.in. [WouterVH]

• Break up scaleImage, so that its scaling-related parts can be applied to instances of PIL.Image for further processing. [witsch]

1.2.2 - 2010-09-28

• Re-release to fix bad egg created for 1.2.1. Refs http://dev.plone.org/plone/ticket/11154 [witsch]

1.2.1 - 2010-08-18

• Convert CMYK to RGB, allowing for web previews of print images. [tomster]

1.2 - 2010-07-18

• Update package metadata. [hannosch]

1.1 - 2010-04-20

• Abort if thumbnail behaviour is requested but either width or height is missing. This is nicer than confronting the caller with a PIL exception. [wichert]

• Rename the keep direction to thumbnail to make its behaviour more intuitive, but accept keep for now. [wichert]

1.0 - 2010-04-12

• Only pull in the uuid distribution in Python versions before 2.5. [hannosch]

• Don’t declare dependency on PIL. [davisagli]

1.0a2 - 2010-04-10

• Add BSD license text following board decision: http://lists.plone.org/pipermail/membership/2009-August/001038.html [elro]

• Allow to use PIL’s thumbnail algorithm to keep the present aspect ratio. [spamsch, witsch]

• Allow to set the quality of the resulting image scales. [witsch]

• Refactor storage adapter for image scales to be less dependent on the underlying content type. [witsch]

1.0a1 - 2009-11-10

• Initial release [wichert]