Products.WatermarkImage 1.0

Data storage

WatermarkImage instances take the original image data, store it on the instance, and generate a watermarked image as well as a thumbnail, which are stored on the instance as well. The watermarked image is stored as the main image, so all normal image access will return the watermarked image. The thumbnail is a scaled-down copy of the watermarked image.

Thumbnail support

Whenever a WatermarkImage is created or updated, a thumbnail is generated as well. Thumbnail data can be viewed using the ZMI (Zope Management Interface) on the Thumbnail tab. Its data can be accessed by adding /thumbnail.jpg to the WatermarkImage URL. A new method tag_thumbnail can be used to generate a HTML img tag for the thumbnail image, its arguments are the same as the standard Zope Image’s tag method.

The following WatermarkImage properties affect thumbnail generation:

• Maximum thumbnail height (pixels): The maximum height for the generated thumbnail. Thumbnails retain the original image’s height/width ratio, so the actual thumbnail height may be less than the maximum height specified here.

• Maximum thumbnail width (pixels): The maximum width for the generated thumbnail. Thumbnails retain the original image’s height/width ratio, so the actual thumbnail width may be less than the maximum width specified here.

If you change any of these properties through the ZMI Properties tab, the thumbnail will be regenerated automatically to reflect the new values.

Watermarking support

If the user specifies that a watermarked image should be created, any image upload to the WatermarkImage instance as well as property updates on the ZMI Properties tab will generate a watermarked copy of the original image. The original image data can be viewed using the ZMI on the Edit Original tab. Its data can be accessed by adding /original to the WatermarkImage URL. A new method tag_original can be used to generate a HTML img tag for the original image, its arguments are the same as the OFS.Image’s tag method.

Access to the original image is protected by a new Zope Permission named WatermarkImage: View original. This permission is only granted to the Zope Manager role by default. You can use the ZMI Security tab to change this default setting.

The following WatermarkImage properties affect the watermarking support:

• Watermark ID: The Zope Id of a standard Zope Image instance containing the actual watermark to be placed onto the image.

• Watermark opacity: The opacity value determines how opaque the watermark will appear on the watermarked image. Its value must be betwen 0 and 1. Opacity 0 will create a transparent watermark, while opacity 1 will apply the watermark image without any transparency manipulation.

• Watermark use: Select whether to create no watermark at all (none), position a single watermark in a specific place on the image (position), tile as many copies of the watermark image onto the image as possible (tile), or place a single watermark onto the image, scaled to the original image size (scale).

• Watermark position on X-axis: Only applicable if position has been selected under Watermark use. The watermark’s top left corner will be placed further to the right by the number of pixels set here. If you specify a negative value, placement will be determined by subtracting the provided value from the original image’s width in order to allow right-aligned positioning.

• Watermark position on Y-axis: Only applicable if position has been selected under Watermark use. The watermark’s top left corner will be placed lower by the number of pixels set here. If you specify a negative value, placement will be determined by subtracting the provided value from the original image’s height in order to allow bottom-aligned positioning.

If you change any of these properties through the ZMI properties tab, the watermarked image and the thumbnail will be regenerated automatically to reflect the new values.

Changing configuration defaults

A user can configure several settings on a per-instance basis which influence thumbnail and watermarked image generation. However, doing so for every WatermarkImage instance is tedious. Instead, a set of configuration defaults can be defined in your Zope instance’s zope.conf configuration file. Simply add a stanza named product-config watermarkimage and define new defaults:

<product-config watermarkimage>
  watermark_use position
  watermark_position_x 100
  watermark_position_y -100
  thumbmail_max_height 100
  thumbnail_max_width 100
</product-config>

The following keys and their corresponding setting on the ZMI Properties tab are recognized:

• watermark_use: corresponds to Watermark use

• watermark_position_x: corresponds to Watermark position on X axis

• watermark_position_y: corresponds to Watermark position on Y axis

• watermark_opacity: corresponds to Watermark opacity

• watermark_id: corresponds to Watermark ID

• thumbnail_max_height: corresponds to Maximum thumbnail height (pixels)

• thumbnail_max_width: corresponds to Maximum thumbnail width (pixels)

Please note: When you set a default in zope.conf, it will be applied to the WatermarkImage instance at creation time. Subsequent changes in the zope.conf default values will not influence existing instances.

Bug tracker

If you have suggestions, bug reports or requests please use the issue tracker at http://www.dataflake.org/tracker/

SVN version

You can retrieve the latest code from Subversion using setuptools or zc.buildout via this URL:

http://svn.dataflake.org/svn/Products.WatermarkImage/trunk#egg=Products.WatermarkImage

Changelog

1.0 (2009-05-09)

Initial release.

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