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Andreas Österreicher
219 lines
7.4 KiB
Plaintext
219 lines
7.4 KiB
Plaintext
eZ publish Enterprise Component: ImageConversion, Design
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Introduction
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============
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Purpose of ImageConversion package
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----------------------------------
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The ImageConversion package will be utilized to convert existing images
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in different ways:
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- Conversion between MIME types (e.g. image/BMP -> image/JPEG,...)
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- Resizing image files (e.g. scaling, cropping,...)
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- Filtering image content (e.g. change of color pallet, add noise,...)
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Current implementation
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----------------------
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Currently the described functionality is implemented utilizing the following
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classes, inside the library lib/ezimage/:
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eZImageManager
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Controller for the other classes utilized in this library. Handles
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configuration, dispatches the necessary action to the different classes.
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eZImageHandler
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Baseclass for image handlers. Provides common methods between image
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handlers and defines a common API.
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eZImageGDHandler
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Image handler implementation for ext/GD2. Extends eZImageHandler.
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eZImageShellHandler
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Image handler implementation for Image Magick. Extends eZImageHandler.
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General notes
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-------------
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The idea behind the design chosen for this class is definitly the right one,
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but it could have been much more modulized to gain a more clean code layout
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and more flexibillities. Beside that, the user interface seems pretty unclear
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and needs some general revision.
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Requirenments
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=============
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Design goals
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------------
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Several goals have to be kept in mind while re-designing the implemented
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functionality:
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- Do not reduce possibilities, but enhance them.
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- Create a more clean user interface and enhance usabillity.
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- Raise flexibillity regarding backends and filter definition.
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- Keep the code fast.
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Detailed requirenments
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----------------------
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The ImageConversion component allows to deal with quite complex image
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conversions in an easy to use ways. Beside that it handles automatic
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conversions, if necessary, like converting incoming image formats to a range
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of range of wanted output formats. This paragraph tries to summarize, what
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exactly has to be done by ImageConversion:
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Conversion between image formats
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In general, ImageConversion should be able to convert images between MIME
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types utilizing it's backends. Conversions must be globally defineable to
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allow forcing of conversions (like for GIF -> PNG). Since some image
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formats have special cases, in which a conversion is not possible (like
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animated GIF), it must be possible to define exceptions for conversion.
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Beside the global conversion, it has to be possible, to convert images
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explicitly. Format conversions can ba parameterized (like the compression
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factor for JPEG, the colorpallet for GIF,...). The conversions possible
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depend on the image handlers available.
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Filtering of image contents
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Filtering of images can have a lot of incarnation in this case:
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Geometry manipulation
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down/up only, keep/change ratio, with/height only,...
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Attribute manipulation (was: colorspace)
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transform color space, change quality,...
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Content manipulation
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adding noise, swirrling, adding borders...
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Which filters are available depends highly on the available image
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handlers, their version and maybe other factors in respect to them (PHP
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version,...).
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Every filter can have a variaty of options and settings to influence its
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behaviour. Options and settings maybe completly different between filters.
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Definition of image formats
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To reduce the overhead of manually defining, which filters have to be
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applied to an image to achieve a certain goal (like "create a
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thumbnail", "create a preview", "make it look like an old photo",...), the
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definition of different image formats should be allowed. A format
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definition can include all of the above stated transformations.
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Beside that, it has to be possible to define, that a format is based on
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another format (like a thumbnail should be created from a preview, to
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reduce conversion ammount). If a format references another format, this
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reference format will be created first (if it does not exist) and
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conversion to the target format will take place afterwards. This allows to
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define a tree of format conversions. Every node of the tree should be
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saved for later utilization.
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Currently, this formats are called aliases.
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Design
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======
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ezcImageConverter
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-----------------
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The main class of the component is the ezcImageConverter, which dispatches the
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actions performed on images, holds the ezcImageHandler's (which actually perform
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the actions) and manages / defines the ezcImageTransformations which hold
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conversions and filters.
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Since 1 filter/conversion can be performed by several ezcImageHandler's, the
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manager has a preference list, to determine, which ezcImageHandler to take for
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a conversion.
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ezcImageHandler
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---------------
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This interface defines how the abstraction class for an image handler looks
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like. ezcImageHandler's utilize a given backend to perform conversion and
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filtering (using ezcImageFilter's). A ezcImageHandler knows by hisself, which
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filters he implements. The manager will ask it for supported filters to get an
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overview, which filters exist.
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To avoid reopening an image file for every operation the ezcImageHandler has
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load()/save() methods. An image must be saved before another ezcImageHandler
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can perform his actions on it.
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ezcImageFilters
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---------------
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[[[------UPDATE NEEDED HERE!--------]]]
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This class implements a storage container for filters to keep them better
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consistant than an array could do. Filters are created by the ezcImageManager
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or directly through a ezcImageHandler. An ezcImageFilter knows, to which
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handler he belongs and dispatches itself to the right handler, when applied.
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ezcImageTransformation
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----------------------
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ezcImageTransformation's abstract image types to allow the easy combination of
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conversions between MIME types and filters which are necessary to get a desired image type.
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For conversions only the target MIME type is necessary.
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ezcImageTransformation's will be created on the fly, when the user requests them and not
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during startup of the manager. A created ezcImageTransformation will be cached in the
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manager for possible later use. Same applies to the filters utilized by the
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ezcImageTransformation.
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Example 1
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^^^^^^^^^
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====================== =======================
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Transformation: Preview
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MIME: image/JPEG
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image/PNG
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Filters: scale 400x400
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====================== =======================
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Example 2
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^^^^^^^^^
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====================== =======================
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Transformation: Thumbnail
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MIME: image/JPEG
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image/PNG
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Filters: scale 100x100
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colorspace grey
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====================== =======================
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Will scale down the image to 100x100 pixels and convert it to greyscale.
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Example 3
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^^^^^^^^^
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====================== =======================
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Transformation: OldPhotos
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MIME: image/JPEG
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Filters: colorspace grey
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border 3
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====================== =======================
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Will convert the inserted image to image/JPEG, reduce the colorspace to
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greyscale and add a border of 3 pixel.
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^L
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..
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Local Variables:
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mode: rst
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indent-tabs-mode: nil
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sentence-end-double-space: t
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fill-column: 79
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End:
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vim: et syn=rst tw=79 wrap
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