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Image support and display
Reading devices can adapt images to the display size and color depth of a specific device. The ebook designer should only strive to provide the highest-quality images for his books, and let the Mobipocket Reader display them optimally on each device.
For large images, The Mobipocket Reader includes an image viewer that lets users scroll and zoom the image and benefit from its full resolution.
Mobipocket Creator will automatically resize / recompress images that take too much space so you do not have to worry about over-burdening your book with high-resolution pictures. The limit is 63KB (63x1024 bytes). Images above that size are resized or recompressed. With the JPEG format, this lets you use images of 600x800 pixels and above. If you need to finely control the resizing / recompressing of your pictures, use an image editing software to bring the size of the image below 63K in GIF or JPEG format before using it in your publication. It will be stored in the book without any modification.
Mobipocket Reader does not support vector graphics. You will have to convert your vector graphics into raster graphics (GIF).
To add an image in the flow of the HTML, simply use the standard HTML syntax
align, border, width and
height attributes are all supported. width & height attributes
can be used to implement a "thumbnail" version of an image.
However, contrary to web rowser rendering, specifying an width / height larger than the actual image
will not have any effect (images are not scaled up).
The align attribute can be used on image to specify its vertical alignment in the current line or relatively to the text of the line.
Baseline and bottom produce the same result.
Adapting images to various screen resolutions
The IMG tag in Mobipocket publications supports up to three source attributes for various resolutions: src, losrc and hisrc. This makes it possible to optimize the same ebook for various devices. The image to be displayed is dynamically selected by the Reader according to the resolution of the screen on the actual device. This feature is useful for bullets or icons and also for words rendered as images. It is of no use for photographs because the Mobipocket Reader can already scale them correctly to the screen size.
Example:<img hisrc="button_for480x640.gif" src="button_for220x300.gif" losrc="button_for140x140.gif"/>
A cover should NOT be an HTML page with an image in it. The Mobipocket file format can store an image as the logical cover of a book. Please read the Cover Page article for more information.
Image quality guidelines
RULE #1: For photo-like images: use color images in JPEG format with a maximum of resolution (800x600 pixels and beyond). Here is an example of a photograph that can appear in an ebook (size: 960x669 pixels, 62KB)
RULE #2: try to avoid images with text inside as much as possible. Render framed paragraphs in HTML, not as images. Reformat very large tables to make them reflowable. Read the Table support article for more tips on how to handle large tables and complex layout. Here is an example of what should definitely NOT be rendered as an image. Use HTML for this type of layout:
RULE #3: if you have to produce images with text inside (graphics, mathematical equations, tables), make sure they are of good quality. Text in images tends to degrade very quickly when an image is resized and/or compressed. Use the GIF format for images with text because JPEG compression introduces compression artifacts. Decrease the color depth of your GIFs to achieve better compression and get the file size below the 63KB limit, otherwise Mobipocket Creator will recompress the image and the result, on a text image, will be a loss of quality. Here are a few examples of good and bad text-based images.
RULE #4: An image with text in it should not be significantly larger than a screen. User experience degrades rapidly when the user has to scroll through a large image to read the text in it. The rule is that a picture with text inside should NOT be larger than 500x600 pixels and should not contain text with a body size (height of an “a”) of less than 6 pixels. This effectively limits the size of tables rendered as pictures. Larger tables should be reformatted. See the Table support article for more information.
Here is an image with text at the maximum allowed size for this kind of image (500x600 pixels). Text body size (height of an "a") is 7 pixels in this image.
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