File sizes - why the difference?

Araucaria · 11-22-2011, 02:01 PM

A friend gave me a copy of a long and well-known book in mobi format. The file size was then about 2500KB. I have the hardback original which is 350 pages or a bit more, plus a couple of illustrations. To my annoyance, I found that a page had been repeated in digitising it, starting half-way through a sentence. In fact it had been repeated a second time, too. Not having a mobi file editor, I used Calibre to convert it into an epub file, then opened it in Sigil and deleted the repeated passages (just two pages). I then used Calibre to convert it back to a mobi file.

To my surprise, the resulting mobi file is less than half the size of the original, just over 1000KB. But apparently it's just the same as the original (but two pages smaller). For the rest of the book, I couldn't spot any difference at all in what was on my Kindle.

I'm sure there's a simple explanation, but I can't imagine what it is. Can anyone explain?

theducks · 11-22-2011, 02:22 PM

Quote:

Originally Posted by Araucaria

A friend gave me a copy of a long and well-known book in mobi format. The file size was then about 2500KB. I have the hardback original which is 350 pages or a bit more, plus a couple of illustrations. To my annoyance, I found that a page had been repeated in digitising it, starting half-way through a sentence. In fact it had been repeated a second time, too. Not having a mobi file editor, I used Calibre to convert it into an epub file, then opened it in Sigil and deleted the repeated passages (just two pages). I then used Calibre to convert it back to a mobi file.

To my surprise, the resulting mobi file is less than half the size of the original, just over 1000KB. But apparently it's just the same as the original (but two pages smaller). For the rest of the book, I couldn't spot any difference at all in what was on my Kindle.

I'm sure there's a simple explanation, but I can't imagine what it is. Can anyone explain?

Many conversions leave kruft from the original source or previous (program x) conversion.
Calibre has its own process and may clean up a lot of inline code (style sheet stuff...)
Sometimes... Just sometimes. A odd original coding may result in a larger file.

user_none · 11-22-2011, 03:18 PM

Sigil and calibre both perform cleaning of the internal markup. Also calibre produces compressed MOBI files by default. The starting MOBI may not have been using compression.

Araucaria · 11-22-2011, 04:31 PM

Thanks guys, very helpful. It seemed a bit spooky!

baliantas · 11-22-2011, 07:52 PM

Hello Araucaria,

You might also keep in mind that Calibre resizes images based on the output profile you chose in the conversion settings ("page setup"). This might result in a drastically smaller epub/mobi file... That's my experience at least.

11-22-2011, 02:01 PM	#1
Araucaria Bibliophile Posts: 166 Karma: 934516 Join Date: Jul 2011 Location: Cantal in the French Auvergne Device: Kindle Voyage, Kobo Libra H20, Kindle PW2, Moon Pro on Lenovo tablet	File sizes - why the difference? A friend gave me a copy of a long and well-known book in mobi format. The file size was then about 2500KB. I have the hardback original which is 350 pages or a bit more, plus a couple of illustrations. To my annoyance, I found that a page had been repeated in digitising it, starting half-way through a sentence. In fact it had been repeated a second time, too. Not having a mobi file editor, I used Calibre to convert it into an epub file, then opened it in Sigil and deleted the repeated passages (just two pages). I then used Calibre to convert it back to a mobi file. To my surprise, the resulting mobi file is less than half the size of the original, just over 1000KB. But apparently it's just the same as the original (but two pages smaller). For the rest of the book, I couldn't spot any difference at all in what was on my Kindle. I'm sure there's a simple explanation, but I can't imagine what it is. Can anyone explain?

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11-22-2011, 03:18 PM	#3
user_none Sigil & calibre developer Posts: 2,488 Karma: 1063785 Join Date: Jan 2009 Location: Florida, USA Device: Nook STR	Sigil and calibre both perform cleaning of the internal markup. Also calibre produces compressed MOBI files by default. The starting MOBI may not have been using compression.

11-22-2011, 04:31 PM	#4
Araucaria Bibliophile Posts: 166 Karma: 934516 Join Date: Jul 2011 Location: Cantal in the French Auvergne Device: Kindle Voyage, Kobo Libra H20, Kindle PW2, Moon Pro on Lenovo tablet	Thanks guys, very helpful. It seemed a bit spooky!

11-22-2011, 07:52 PM	#5
baliantas Junior Member Posts: 9 Karma: 10 Join Date: Feb 2011 Device: Sony PRS-350	Hello Araucaria, You might also keep in mind that Calibre resizes images based on the output profile you chose in the conversion settings ("page setup"). This might result in a drastically smaller epub/mobi file... That's my experience at least.