Tip - output profile setting can dramatically slow down conversion

andrewburt · 11-28-2015, 01:57 PM

Just an FYI... I learned this the hard way

and thought I might save someone else a bit of (conversion) time.

The "output profile" setting in Page Setup can have a HUGE impact on conversion times.

I didn't realize when picking "ipad" as the output device that it would run, in my case, 7x slower than the "Default Output Profile." Ouch!

(I didn't realize this for years, until I ran a conversion from the command line on the same PC using ebook-convert, and it was 7x faster. That got me to digging around for the cause.)

I looked at the .mobi output from both "ipad" and "default" profiles, and to my eye, I couldn't see any difference in text or images, so it may be worth your while to try different output profiles for speed.

I've only tested this on epub -> mobi conversions, don't know if it impacts other output formats or not.

Hope this helps save folks some time.

kovidgoyal · 11-28-2015, 10:49 PM

That's because maximum allowed image size is higher, which means that the mobi output plugin has to do much more work (re-encoding images with lower and lower quality settings) to fit large images into the size constraints imposed by the mobi format.

andrewburt · 11-29-2015, 12:30 PM

Hi, Kovid, thanks for the explanation!

So, is there an output profile (such as, perhaps, "Default Output Profile")

that does -no- image resizing, and just leaves the images as-is?

I'm thinking particularly if one is making a single .mobi for different size output devices, there's no "right" size, so not re-encoding the images at all would be the simplest (as well as fastest) approach.

If it's feasible, that is: What image file formats does a .mobi handle natively, without re-encoding? Or does it require re-encoding no matter what?

Thanks!

kovidgoyal · 11-29-2015, 01:56 PM

The MOBI format *requires* images to be resized because it has a max image bytesize limit.

eschwartz · 11-29-2015, 02:03 PM

@Kovid, this is MOBI only, not AZW3, right?

kovidgoyal · 11-29-2015, 03:46 PM

I dont recall, I know it is for certain in MOBI, but in azw3 there may be a different limit imposed by the max size of a PDB record, you'll have to check the source.

11-28-2015, 01:57 PM	#1
andrewburt Science Fiction Writer Posts: 231 Karma: 124188 Join Date: Dec 2010 Location: Golden, CO Device: several	Tip - output profile setting can dramatically slow down conversion Just an FYI... I learned this the hard way and thought I might save someone else a bit of (conversion) time. The "output profile" setting in Page Setup can have a HUGE impact on conversion times. I didn't realize when picking "ipad" as the output device that it would run, in my case, 7x slower than the "Default Output Profile." Ouch! (I didn't realize this for years, until I ran a conversion from the command line on the same PC using ebook-convert, and it was 7x faster. That got me to digging around for the cause.) I looked at the .mobi output from both "ipad" and "default" profiles, and to my eye, I couldn't see any difference in text or images, so it may be worth your while to try different output profiles for speed. I've only tested this on epub -> mobi conversions, don't know if it impacts other output formats or not. Hope this helps save folks some time.

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11-28-2015, 10:49 PM	#2
kovidgoyal creator of calibre Posts: 45,611 Karma: 28549044 Join Date: Oct 2006 Location: Mumbai, India Device: Various	That's because maximum allowed image size is higher, which means that the mobi output plugin has to do much more work (re-encoding images with lower and lower quality settings) to fit large images into the size constraints imposed by the mobi format.

11-29-2015, 12:30 PM	#3
andrewburt Science Fiction Writer Posts: 231 Karma: 124188 Join Date: Dec 2010 Location: Golden, CO Device: several	Hi, Kovid, thanks for the explanation! So, is there an output profile (such as, perhaps, "Default Output Profile") that does -no- image resizing, and just leaves the images as-is? I'm thinking particularly if one is making a single .mobi for different size output devices, there's no "right" size, so not re-encoding the images at all would be the simplest (as well as fastest) approach. If it's feasible, that is: What image file formats does a .mobi handle natively, without re-encoding? Or does it require re-encoding no matter what? Thanks!

11-29-2015, 01:56 PM	#4
kovidgoyal creator of calibre Posts: 45,611 Karma: 28549044 Join Date: Oct 2006 Location: Mumbai, India Device: Various	The MOBI format requires images to be resized because it has a max image bytesize limit.

11-29-2015, 02:03 PM	#5
eschwartz Ex-Helpdesk Junkie Posts: 19,421 Karma: 85400180 Join Date: Nov 2012 Location: The Beaten Path, USA, Roundworld, This Side of Infinity Device: Kindle Touch fw5.3.7 (Wifi only)	@Kovid, this is MOBI only, not AZW3, right?

11-29-2015, 03:46 PM	#6
kovidgoyal creator of calibre Posts: 45,611 Karma: 28549044 Join Date: Oct 2006 Location: Mumbai, India Device: Various	I dont recall, I know it is for certain in MOBI, but in azw3 there may be a different limit imposed by the max size of a PDB record, you'll have to check the source.

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