Thread: Aura ONE Kobo Aura One owners thread
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Old 01-30-2017, 12:28 AM   #1104
davidfor
Grand Sorcerer
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Posts: 24,905
Karma: 47303824
Join Date: Jul 2011
Location: Sydney, Australia
Device: Kobo:Touch,Glo, AuraH2O, GloHD,AuraONE, ClaraHD, Libra H2O; tolinoepos
Quote:
Originally Posted by rashkae View Post
With 680 books loaded on my H20, my .kobo-images folder is 527MB, so tracking about the same as Mingyar. It's worth noting that the Kobo generated a full screen size image for all the books, not just the ones I opened. Since the full screen resolution on the One will be significantly higher, I expect the full screen image sizes are probably at least 10 to 20% larger as well.

The large image that Kobo generated are all 1440 px tall, and range in size from 470KB to 1.1MB

Edit: On further investigation, I see the problem,,, the 'Full' Images kobo generated are all saved with jpeg compression at 100, (according to Gimp scale, when saving with original quality, it defaults to 100, and generates about the same file size.)

This behaviour is probably unique to sideloading Kepub. When Kobo sends the file, do they also send optimized cover images?
On the device, for epubs, the first page is rendered and saved. For kepubs, the image that is marked as a cover is extracted, sized appropriately and saved. Both of these are saved with colour and I have never looked at quality level for the images no matter how they were produced. When downloaded from Kobo, the covers are always grey scale ("always" here means "all the ones I looked at and can remember"). From a comment elsewhere, the conversion the server does probably isn't that good.

The calibre image generation is what was there when I took over maintaining the driver. Or I copied it from another driver and only change the size of the images. I've forgotten which now Graphics and image manipulation is not one of my areas of expertise. I know just enough to be dangerous.* If someone wants to suggest some better parameters for generating the covers, I'll look at them. Or maybe a space saving option vs a hires option. Adding options to the driver is a lot easier now, so

* If "a little knowledge is a dangerous thing", I am a very dangerous person.
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