Forma Can I safely delete the ".kobo-images" folder? It's taking 500MB of space. - Page 3

droopy · 10-13-2019, 10:21 PM

Quote:

Originally Posted by NiLuJe

@droopy: From the Library view, select the books you want to update, Kobo Utilities > Upload covers for selected books

This'll pop up the KU popup with the same set of settings discussed earlier.

NiLuJe, I did this with the about 15 of the biggest ebooks in my library. For example, Walter Iscaacson's Leonardo Da Vinci is a 443.7 MB epub.
When I open the kepub.epub on the KoboReader with my laptop, the cover is still full color.

Also, how do I have not just the cover converted into grayscale, but all photographs/maps/illustrations/images within the ebook?

NiLuJe · 10-13-2019, 10:24 PM

@droopy: That only applies to the nickel thumbnails, not the (K)ePub's cover and/or other embedded images.

Nickel itself will grayscale and dither those (at runtime). You could potentially grayscale the JPGs (don't dither 'em yourself though, JPEG is *not* a paletted format, so it'll basically ruin the dithering on encode. Plus, dithering would also actively harm the compression ratio here).
Depending on content, properly dithered & encoded PNGs might even end up being smaller than a grayscale JPG, though, but that's another kettle of fish...

droopy · 10-13-2019, 10:28 PM

Quote:

Originally Posted by NiLuJe

@droopy: That only applies to the nickel thumbnails, not the (K)ePub's cover and/or other images.

Nickel itself will grayscale and dither those.

@NiLuJe, Sorry, I'm not sure i understand. On my laptop (i.e. the "library"), I'd like to keep the original epub/cbr/mobi files, with all the color and everything else untouched. But on my Kobo, I want all images, whether the book's cover or the book's contents, be all grayscale. What must I do to make that happen? The purpose is to save space on my Kobo Forma. (A secondary benefit is probably faster page turns and book loading times.)

NiLuJe · 10-13-2019, 10:32 PM

I'm not quite sure anything like that has been done (except for KCC for the very specific purpose of Comics/Manga). But that's standalone, and implies a conversion (i.e., a copy).

(And, again, JPEG being terrible, I'm not quite sure you'd gain much anyway with something like that on non-Comics/Manga content).

My point being, if you're designing a book with heavy image content for eInk, yeah, definitely process your images properly first. But as a generic go-to processing pass on upload to device, meh.

davidfor · 10-14-2019, 01:01 AM

Quote:

Originally Posted by droopy

@NiLuJe, Sorry, I'm not sure i understand. On my laptop (i.e. the "library"), I'd like to keep the original epub/cbr/mobi files, with all the color and everything else untouched. But on my Kobo, I want all images, whether the book's cover or the book's contents, be all grayscale. What must I do to make that happen? The purpose is to save space on my Kobo Forma. (A secondary benefit is probably faster page turns and book loading times.)

For the comics, calibre doesn't have a comic output plugin, so there isn't a way to convert books of any sort to either CBR or CBZ. Writing one shouldn't be to hard for someone who had the interest. If this is done, if you convert to the same format, calibre will save the original for later use.

You can cheat sort of and use epub as the output and then change the extension to cbz. That conversion will do the work you need on the images. And an epub is a zip file, so unless the CBZ reader checks for other files, it should be fine.

KCC, as mentioned by @NiLuJe, will also do the job. It has options to produce ebubs or CBZ and to resize to a lot of different devices or a custom size. You could use the Open With function in calibre to start it.

I can't comment on the quality or size of the images produced by any of these. I don't really read comics, so I haven't done much experimenting.

droopy · 10-14-2019, 02:46 AM

Hi DavidFor,
Thanks for your input. If I understand correctly, your comment focused solely on comic books (CBR). I only have one comic book on my Kobo. I don't plan to get more comic books.

The other huge files on my Kobo are epubs with images/photographs. These are not comic books, but are rather mostly text with full-color images/maps/photographs. How do I handle these non-comic-book books with large file sizes?

For example, I have Walter Isaacson's Leonardo Da Vinci book at 450MB
or photojournalist's Chris Arnade's book called Dignity at 100MB.

davidfor · 10-14-2019, 03:51 AM

Sorry, I got the impression you were talking about comics.

The only automated way I can think of is using calibre to do a conversion. The Output Profile can be used to set the maximum size of the images. But, it only changes the size of images larger than this. I don't see an option to change the images other than this.

If you just want to change the images to grey scale or otherwise fiddle with the image quality, you can unpack the book and use image manipulation tools on the images and then repack the images. Calibre has a method to make the unpacking/repacking easy. There has been some discussion on doing this in either the calibre forum or the Workshop forum. Searching them should find them.

If you want to resize the images, it is harder. From my experience, the images are embedded in different ways, and each book, or even each image, needs to be handled individually.

10-13-2019, 10:24 PM	#32
NiLuJe BLAM! Posts: 13,506 Karma: 26047202 Join Date: Jun 2010 Location: Paris, France Device: Kindle 2i, 3g, 4, 5w, PW, PW2, PW5; Kobo H2O, Forma, Elipsa, Sage, C2E	@droopy: That only applies to the nickel thumbnails, not the (K)ePub's cover and/or other embedded images. Nickel itself will grayscale and dither those (at runtime). You could potentially grayscale the JPGs (don't dither 'em yourself though, JPEG is not a paletted format, so it'll basically ruin the dithering on encode. Plus, dithering would also actively harm the compression ratio here). Depending on content, properly dithered & encoded PNGs might even end up being smaller than a grayscale JPG, though, but that's another kettle of fish... Last edited by NiLuJe; 10-13-2019 at 10:50 PM.

10-13-2019, 10:32 PM	#34
NiLuJe BLAM! Posts: 13,506 Karma: 26047202 Join Date: Jun 2010 Location: Paris, France Device: Kindle 2i, 3g, 4, 5w, PW, PW2, PW5; Kobo H2O, Forma, Elipsa, Sage, C2E	I'm not quite sure anything like that has been done (except for KCC for the very specific purpose of Comics/Manga). But that's standalone, and implies a conversion (i.e., a copy). (And, again, JPEG being terrible, I'm not quite sure you'd gain much anyway with something like that on non-Comics/Manga content). My point being, if you're designing a book with heavy image content for eInk, yeah, definitely process your images properly first. But as a generic go-to processing pass on upload to device, meh. Last edited by NiLuJe; 10-13-2019 at 10:36 PM.

10-14-2019, 02:46 AM	#36
droopy Guru Posts: 834 Karma: 2912460 Join Date: Apr 2009 Device: Kobo Forma	Hi DavidFor, Thanks for your input. If I understand correctly, your comment focused solely on comic books (CBR). I only have one comic book on my Kobo. I don't plan to get more comic books. The other huge files on my Kobo are epubs with images/photographs. These are not comic books, but are rather mostly text with full-color images/maps/photographs. How do I handle these non-comic-book books with large file sizes? For example, I have Walter Isaacson's Leonardo Da Vinci book at 450MB or photojournalist's Chris Arnade's book called Dignity at 100MB. Last edited by droopy; 10-14-2019 at 02:48 AM.

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10-14-2019, 03:51 AM	#37
davidfor Grand Sorcerer Posts: 24,905 Karma: 47303824 Join Date: Jul 2011 Location: Sydney, Australia Device: Kobo:Touch,Glo, AuraH2O, GloHD,AuraONE, ClaraHD, Libra H2O; tolinoepos	Sorry, I got the impression you were talking about comics. The only automated way I can think of is using calibre to do a conversion. The Output Profile can be used to set the maximum size of the images. But, it only changes the size of images larger than this. I don't see an option to change the images other than this. If you just want to change the images to grey scale or otherwise fiddle with the image quality, you can unpack the book and use image manipulation tools on the images and then repack the images. Calibre has a method to make the unpacking/repacking easy. There has been some discussion on doing this in either the calibre forum or the Workshop forum. Searching them should find them. If you want to resize the images, it is harder. From my experience, the images are embedded in different ways, and each book, or even each image, needs to be handled individually.

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