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Old 12-09-2012, 08:40 PM   #44
bob451 began at the beginning.
Posts: 10
Karma: 28
Join Date: Aug 2010
Device: kobo
The way in which ADE on the KT is liable to throw a screen-break before a "long" paragraph, and to throw further screen-breaks within a "longer" paragraph, is quite noticeable for a font size of 24. (That corresponds roughly to "Medium" on the Kobo Original.)

For the next font size down on the KT, the effect is nowhere near as noticeable.

I suspect it is related to the way in which ADE determines what is a "page". In the Adobe document, "EPUB Best Practices", is the following section:

Synthetic page names

When page map is not available in the document, Adobe Digital Editions will synthesize a page-map based on the document content. The approach used is the following:

1. Determine a compressed byte length of each resource which is referenced in the spine, subtracting any known encryption overhead (IV size)

2. Assume that there is a page for each 1024 bytes in each resource, rounding up to the nearest whole number of pages for each resource

3. To map page breaks into a resource, use the number of pages for the resource as determined in step 2, count the number of Unicode characters in the resource; distribute synthetic page breaks in the resource evenly between the characters by dividing the number of characters by the number of pages; if the number of characters don't divide evenly among the pages, round the number of characters per page up and let the last 'page' contain less characters than the rest.
That typically means a bit more than 500 "words" per "page". For my setup with font size 24, that corresponds to perhaps 54 screen lines (over 2 screens with 24 lines/screen).

If text for a "resource" (chapter) were to flow continuously from screen to screen, each synthetic "page" may begin at any screen line; a synthetic "page" will usually not correspond to an integral number of screens. Thus, it would be ridiculous for ADE to have a new synthetic "page" start on a new screen, and it doesn't do that normally. The "page" number, whether for display or navigation purposes, simply need refer to the screen display containing the "page" break.

Why then is ADE liable to throw a screen-break before a "long" paragraph, and to throw screen-breaks within "longer" paragraphs? It seems to depend on the current position within the synthetic "page", the current position on the screen, and the length of the paragraph (or the remaining number of screen lines in a "longer" paragraph); different "long" paragraphs of identical numbers of screen lines may show different screen-breaks.

For some reason, ADE seems to confuse "screen-breaks" and "page-breaks". And I can't for the life of me see why it needs to do that. In practice, for a font size of 24, to keep "screen-break-before" occurrences down to an acceptable level and to eliminate "screen-break-within" occurrences, I have found it necessary to restrict "paragraphs" to about 250 words.

I did try epubs with a page-map file to tell ADE that the resource (chapter) has no pages (<page name="" .../>), so that each chapter appeared to be of 1 page (it was a useful way to get rid of the RHS page number displayed on the Kobo Original). No change: ADE still threw screen breaks in the same places, so it was still working on synthetic pages internally.
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