How to turn all images in Kobo Forma to grayscale (to save space & speed xp)

[droopy]

I have a Kobo Forma. Almost all my ebooks come with an image for the cover, and when they don't, I get Calibre to find and download a cover.

Some of my ebooks come with images. For example, maps and photographs. Almost always, these images are full colors, unless the photos are from, um, the 1970s or earlier when film was still black and white or grayscale.

Because my Forma only does grayscale, I would like all images that are in my Kobo Forma to be grayscale. This is to save on limited space (and perhaps a secondary benefit is faster page turns / image-loading).

How can I make this happen?

[theducks]

Let me get what you want straight:
You want ALL images to be grey scale, not just covers?

For that, you need to Unpack (U in Calibre), process the images with you favorite tool (I used to use Paintshop Pro), then save (the Unpack tool has remained open all this time). Note: This process is performed on the LIBRARY COPY, COLOR IS GONE for good

[retiredbiker]

Another way to save space is to simply compress the images. Open the book in the editor, and there is a tool: Tools-->Compress images losslessly. This will give you some, usually small, compression, but in the dialogue there is a box to check for Enable lossy compression of JPEG images. Set this to about 50 in the compression quality box and it can save you significant space. A 1.5 mb jpg may go down to 150 kb...on that order, anyway.

I have a Forma, and found that this drastic compression has no visible effect on the picture you see on the reader. It is very fast and will do all the images at once. But if you have big png images it won't help much, and takes a long time.

[droopy]

Originally Posted by theducks

Let me get what you want straight:

You want ALL images to be grey scale, not just covers?

Yes, all images, including covers but not just covers.

Originally Posted by theducks

For that, you need to Unpack (U in Calibre), process the images with you favorite tool (I used to use Paintshop Pro), then save (the Unpack tool has remained open all this time). Note: This process is performed on the LIBRARY COPY, COLOR IS GONE for good

I don't want the library copy touched

[theducks]

Originally Posted by droopy

Yes, all images, including covers but not just covers.




I don't want the library copy touched

Then you need to do this process using Device view, knowing that any update of that book will be undoing it.
That is, unless David thinks that is worth the effort to add to that option Kobo Utilities.
Is the Forma really so under performing (compared to my Aura 2), that you need to wring out this last bit of performance?

[NiLuJe]

It won't have any perceivable effect on performance. In fact, having grayscale content might make it *worse*, because nickel is not running in grayscale (because Qt).

The only interest in carefully grayscaled content is when you care about accuracy and/or file size.

[droopy]

I want to greyscale every image not just for performamce but also for storage space

[droopy]

Originally Posted by theducks

Then you need to do this process using Device view, knowing that any update of that book will be undoing it.
That is, unless David thinks that is worth the effort to add to that option Kobo Utilities.
Is the Forma really so under performing (compared to my Aura 2), that you need to wring out this last bit of performance?

I have an ebook called Leonardo Da Vinci by Walter Isaacson. It's 450 MB because of the images. 450 mb is already 1/16 of my 8GB Forma space. Why transfer full-color images:
if I can't even enjoy the color,
if I can save storage space,
If I can speed page-loads/turns?

[davidfor]

Originally Posted by droopy

I have an ebook called Leonardo Da Vinci by Walter Isaacson. It's 450 MB because of the images. 450 mb is already 1/16 of my 8GB Forma space. Why transfer full-color images:
if I can't even enjoy the color,
if I can save storage space,
If I can speed page-loads/turns?

Before you do anything else, you should open that book and look at the images. Are they actually high resolution? And try fiddling with a few to see what effect it actually has.

And as @NiLuJe, Kobo actually renders in colour. I assume it is writing to the screen that does the gray-scaling. I suspect you won't get any noticeable performance benefit. I would say that space is the only advantage and you can test this manually to see if it is actually worthwhile following it up. Try what @theducks suggested.

Also, this question has come up before. But, no-one has developed a tool to do it. I suspect that means that people who have tried it have found it isn't worth it. Or, they decided that the colour was important and used a tablet for books with lots of pictures. Which is what I would do,

[ratinox]

If these are not CBZ/CBR files then converting to greyscale probably isn't going to help much overall. If these are CBZ/CBR files then transcoding may be beneficial. Or it might not. There's very much an "it depends" involved. But for the most part I get good results with ImageMagick:

KX=1440; KY=1920
GREY="-type Grayscale -level 0%,100%,0.6"
BLUR="-gaussian-blur 0.05"
TRIM="-trim +repage"
FUZZ="-fuzz 1%"
mogrify -verbose -strip -format jpg -quality 85% ${FUZZ} ${TRIM} ${BLUR} -filter Lanczos -resize ${KX}x${KY} ${GREY} *

But realistically? I read my comics and manga on my iPad Mini now.

[ratinox]

Originally Posted by davidfor

And as @NiLuJe, Kobo actually renders in colour. I assume it is writing to the screen that does the gray-scaling. I suspect you won't get any noticeable performance benefit. I would say that space is the only advantage and you can test this manually to see if it is actually worthwhile following it up. Try what @theducks suggested.

Pretty much. Blitting to the display is what converts color to greyscale so greyscale conversion of source images isn't going to get you much of anything for performance.

Converting from 16/24/32-bit deep color to 8-bit greyscale may save some space but the reason I do it is to minimize artifacts when the display hardware does it on the fly. My commands include some blur and fuzz in order to reduce visible artifacts and take advantage of efficiencies in the JPEG libraries.

Using jpegtran to optimize JPEG files or optipng to optimize PNG files may help reduce image file sizes by a few percent if they haven't already been optimized.

Performance gains can be had by scaling to the native resolution of the display so that the renderer doesn't have to spend procesor cycles (and battery) scaling on the fly. This can either increase or reduce image file sizes depending on the source resolutions and depths.

[NiLuJe]

Technically, Nickel runs @ 32bpp, so it's happily blitting to the framebuffer in BGRA, and leaving the EPDC/PxP to do the grayscaling, followed by a decimating quantization pass (unless you're on a Mk. 7, in which case it does an ordered dithering pass).

Which means feeding a grayscale image to Qt nets you an implicit conversion to RGB32 behind the scenes .

Note that, as was mentioned earlier, there are probably a number of circumstances where you won't be able to avoid scaling entirely (even if it's for something stupid like a 12 pixels margin or something). Still, you can't go wrong with the native screen's resolution, because at least you can be sure that nothing will ever ask for *larger* than that .

That said, we've pretty much all agreed on the fact that both performance and experience in an image-heavy CB(Z|R)/PDF/(K)ePub was going to be fantastically awful in Nickel anyway, so, meh.

[droopy]

Originally Posted by retiredbiker

Another way to save space is to simply compress the images. Open the book in the editor, and there is a tool: Tools-->Compress images losslessly. This will give you some, usually small, compression, but in the dialogue there is a box to check for Enable lossy compression of JPEG images. Set this to about 50 in the compression quality box and it can save you significant space. A 1.5 mb jpg may go down to 150 kb...on that order, anyway.

Is there a way to do this for the ebook on the Forma, but keep the images in the library (i.e., the original copy of the book) untouched?

[droopy]

Originally Posted by ratinox

If these are not CBZ/CBR files then converting to greyscale probably isn't going to help much overall. If these are CBZ/CBR files then transcoding may be beneficial. Or it might not. There's very much an "it depends" involved. But for the most part I get good results with ImageMagick:

KX=1440; KY=1920
GREY="-type Grayscale -level 0%,100%,0.6"
BLUR="-gaussian-blur 0.05"
TRIM="-trim +repage"
FUZZ="-fuzz 1%"
mogrify -verbose -strip -format jpg -quality 85% ${FUZZ} ${TRIM} ${BLUR} -filter Lanczos -resize ${KX}x${KY} ${GREY} *

But realistically? I read my comics and manga on my iPad Mini now.

The 450 MB book titled "Leonardo Da Vinci" is not a CBZ/CBR file. It comes as an epub file.

[droopy]

Originally Posted by davidfor

Before you do anything else, you should open that book and look at the images. Are they actually high resolution? And try fiddling with a few to see what effect it actually has.

In Calibre, I right-clicked the 500MB ebook and chose "Edit Book". In the left section of the book editor, I scrolled to the Images section and chose a 3.8MB jpg. Yup, it's high-res all right: 1390 x 2000 px. This ebook has a lot of these high-res, several-megabyte JPEG files.

Originally Posted by davidfor

And as @NiLuJe, Kobo actually renders in colour. I assume it is writing to the screen that does the gray-scaling. I suspect you won't get any noticeable performance benefit. I would say that space is the only advantage and you can test this manually to see if it is actually worthwhile following it up. Try what @theducks suggested.

I understand that space may be the only advantage. If I could shrink this 450MB ebook down, it would open up a lot of space for more ebooks.

Originally Posted by davidfor

Also, this question has come up before. But, no-one has developed a tool to do it. I suspect that means that people who have tried it have found it isn't worth it. Or, they decided that the colour was important and used a tablet for books with lots of pictures. Which is what I would do,

Color is important, especially for this biography of an artist! My plan is to read the text on my Forma and enjoy the full-color, high-res images on a colored device like my laptop.