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Publishers face a challenge in that iPads and iPhones include both SD (Standard Definition) and HD (High Definition) models. One approach is to create a single folio that works on both SD and HD models. However, without creating multi-rendition articles, some content appears pixelated on the HD device, and some overlays behave differently. Another approach is to create different renditions for both the SD and HD models. However, renditions are somewhat difficult to maintain for some publishers, and single-issue apps do not support multiple folio renditions.
By creating multi-rendition articles, you can create a single 1024x768 folio with PDF articles that look great and perform well on both SD and HD iPads. When you create an article with a PDF image format, the PDF images now have a higher resolution than in previous versions (as high as 108 ppi instead of 72 ppi). While a multi-rendition article looks good on the iPhone 5, the content is letterboxed. For best results, create a separate 1136x640 rendition.
This feature applies only to iOS apps. For Android and Windows apps, content in any article format is scaled up or down and letterboxed as needed.
Note: If you want to use a resolution higher than 108 ppi for certain images, you can make that image a high-resolution overlay, such as an image sequence with only one image file.
In addition, you can perform the following tasks to create a multi-rendition PDF article:
Use a vector format for slideshows and scrollable frames
When you select a slideshow or scrollable frame object, the Folio Overlays panel displays an Export Format in PDF Articles option that lets you choose either Raster or Vector. If you select Vector, content—especially text—in slideshows and scrollable frames appears crisper on HD devices. However, vector content takes longer to load than raster content. For best results, use the Vector option for text-heavy content and Raster for image-heavy content.
Make sure that your folio viewer version is v23 or later. Otherwise, this option has no effect.
Unfortunately, there is no vector option for buttons. Buttons are downsampled to 72 ppi (not 108), causing button text to appear pixelated in some cases. A workaround is to create an image for the button and place an invisible button over that image.
Use different interactive assets for SD and HD devices
This feature is especially useful for pan and zoom images, but it can also be used for panoramas, image sequences, videos, and audio controller skins. You can include two different sets of assets. To do this, you create a subfolder called “HD” in the folder containing the SD assets. In the HD folder, use high-resolution images with identical names to the SD assets. In the Folio Overlays panel, link to the folder containing the SD assets. The viewer on the SD iPad displays one set of assets, and the HD iPad viewer displays the assets in the HD folder.
The HD assets for pan & zoom, image sequence, and audio skins must have twice the dimensions as the SD assets. For example, if an image sequence includes 300x200 SD images in 72 ppi, the HD source files must be 600x400 in 72 ppi.
For videos and pan & zoom images, you can create a single HD folder that includes multiple high-resolution files. For example, if your Links folder includes polarbear.jpg and video01.mp4, you can create an HD folder in the Links folder with high-resolution versions of the polarbear.jpg and video01.mp4 files.
Note that including two sets of assets for overlay types increases the folio size.
We recommend creating two different sets of assets for pan and zoom images in particular. It usually isn’t necessary to create separate SD and HD versions for other overlay types. For example, some publishers create source files for image sequence overlays that fall somewhere between SD and HD resolutions, such as images with a 108 effective ppi. If a high-resolution video plays on an SD iPad, there is no reason to create an additional low-resolution video.