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Old 02-04-2020, 07:50 PM   #61
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Quote:
Originally Posted by NiLuJe View Post
... because Nickel always dithers image content on its own (inline, cover, sleep, roughly all the things that matter in current FW revisions), which we already knew ^^.

*How* it actually does that depends heavily on the specific device, though (and on the FW version. It used to be worse. Which, ironically, was slightly better if your content was pre-processed properly ^^).
The device in question is the original Kobo Aura H2O. What I will try sometime later is the ImageMagik to dither the image and see how that looks on the PW3.
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Old 02-04-2020, 07:57 PM   #62
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Because I've done this before, I had the files on hand .

In practice, putting an image (here, the same torture test) as the cover image in a book will effectively yield that grayscale, ordered dithered thing you see in the second attachment.

I *can* capture those, because it's an H2O with zero hardware/kernel support for dithering.

Results would be different on my Forma .

Fun fact that I don't remember if I'd ever tested before: if I drop the original PNG, and open that, it's displayed entirely unprocessed (again, because H2O).

EDIT: Huh, my full-quality JPEG encode apparently doesn't agree with vB, so I attached the source PNG as a third image, as well as the test ePub. Which I'm pretty sure I originally got from @jackie_w (as well as the original idea to use a double shiny pink gradient pattern for those tests ).

EDIT²: Added the result in sleep mode (with said thumbnail generated by Nickel), to show that there's another process pass involved (or two if you don't use Calibre's Send To Device).
You'll probably have to look at the histogram to truly make the difference pop .

Code:
ePub:

 Colors: 8
  Histogram:
     11455: (0,0,0,65535) #000000FF black
     73325: (9252,9252,9252,65535) #242424FF grey14
    285218: (18761,18761,18761,65535) #494949FF srgba(73,73,73,1)
    206692: (28013,28013,28013,65535) #6D6D6DFF srgba(109,109,109,1)
    134613: (37522,37522,37522,65535) #929292FF srgba(146,146,146,1)
    175086: (46774,46774,46774,65535) #B6B6B6FF srgba(182,182,182,1)
    210374: (56283,56283,56283,65535) #DBDBDBFF grey86
    446557: (65535,65535,65535,65535) #FFFFFFFF white

Sleep:

Colors: 256
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Attached Files
File Type: epub ScreenSaver Test - Aaa Zzz.epub (619.3 KB, 16 views)

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Old 02-04-2020, 08:06 PM   #63
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TL;DR: It's actually technically a crap pattern (even forgetting that it's not 16c, and not the eInk palette), but it works surprisingly well in practice on eInk, as can be gleaned from Jon's picture.

I mean, it's definitely worse than doing it The Right Way, but it's not so awful that I want to tear my eyes off, far from it. And it's definitely a win vs. not doing anything (for unprocessed content, which is 99.99% of content on Kobo) .

On newer devices, what's done looks even better (and isn't as aggressive towards perfect content, which is a double win in my book). The clincher being that it's free on Mk. 7 (in terms of CPU cycles).

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Old 02-04-2020, 08:18 PM   #64
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How do I add PNG images to a Kindle to display?
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Originally Posted by j.p.s View Post
It has changed over time. Sometimes putting a JPEG, GIF, or PNG in the images directory in the root of the mounted kindle file system works and sometimes the required directory is pictures . Either has to be created because they are not there by default. It has been a long time, so I don't know what contemporary kindles require.

But that is the easy part for kindle owners. Where is an example of an image file made with the magical kobo dithering?
I had it wrong the first time. Fixed above.

On my Voyage, it is in /mnt/us/images that is in the images directory at the root of kindle storage mounted on a computer.

The sample images in this thread are shrunk to fit the screen and I can't figure out how to zoom them much less set a 1:1 pixel scale.
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Old 02-04-2020, 08:21 PM   #65
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Quote:
Originally Posted by NiLuJe View Post
TL;DR: It's actually technically a crap pattern (even forgetting that it's not 16c, and not the eInk palette), but it works surprisingly well in practice on eInk, as can be gleaned from Jon's picture.

I mean, it's definitely worse than doing it The Right Way, but it's not so awful that I want to tear my eyes off, far from it. And it's definitely a win vs. not doing anything (for unprocessed content, which is 99.99% of content on Kobo) .

On newer devices, what's done looks even better (and isn't as aggressive towards perfect content, which is a double win in my book. The clincher being that it's free on Mk. 7 (in terms of CPU cycles).).
I find the Kobo dithering interesting. On my H2O, the bit outside the circle looks really good. The bit inside the circle looks good enough. The Forma get the inside of the circle very good and outside of the circle, not as good as the H2O. Now the PW3 doe snot get anything as good as either Kobo.
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Old 02-04-2020, 08:21 PM   #66
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I had it wrong the first time. Fixed above.

On my Voyage, it is in /mnt/us/images that is in the images directory at the root of kindle storage mounted on a computer.

The sample images in this thread are shrunk to fit the screen and I can't figure out how to zoom them much less set a 1:1 pixel scale.
Thanks. I thought there had to be an easier way.
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Old 02-04-2020, 08:22 PM   #67
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@j.p.s: Ah, cool, thanks, good to know that thing is still kicking .

That said, there's a very real chance it's using a completely different rendering codepath than for in-book content .
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Old 02-04-2020, 08:24 PM   #68
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@JSWolf: FWIW, I don't have access to one, but Mk. 6 devices *may* be able to do things differently, as another data set .

(Depends on if the Mk. 6 kernel code matches the Mk. 5 nickel code, which I obviously can't say ^^. What I can say is that I hadn't seen anyone else implement it like that in kernel. Amazon tried some different stuff, but it was mostly aimed towards low-bitdepth experiments. All of this is testable w/ the latest FBInk release, behind the legacy dithering mode, for curious parties with shell access ).

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Old 02-04-2020, 08:47 PM   #69
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@j.p.s: Ah, cool, thanks, good to know that thing is still kicking .

That said, there's a very real chance it's using a completely different rendering codepath than for in-book content .
Same location for KOA2.

Pretty sure it is a different code path on the Voyage, which had severe ghosting, which pretty much defeats judging on board dither quality.

On both KV and KOA2 the full color and 256 gray images look much better than the Forma and sw dither images, both of which start to darken well before getting to outer surrounding black ring and have other artifacts.
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Old 02-04-2020, 09:21 PM   #70
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@j.p.s: Ah, we may be hitting another fun specificity of my test image:

It grayscales fairly specifically differently depending on whether that was done linearly, or gamma-correct.

c.f., https://imagemagick.org/script/comma....php#intensity

The actual Forma_Gray.png linked earlier on GH was actually grayscaled via GIMP, which is not how I usually do it in my full pipeline, but is close enough .

EDIT: Added the GIMP grayscale, and my usual full pipeline result from the full-color one to a "perfect" H2O result.
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Old 02-04-2020, 09:37 PM   #71
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Same location for KOA2.

Pretty sure it is a different code path on the Voyage, which had severe ghosting, which pretty much defeats judging on board dither quality.

On both KV and KOA2 the full color and 256 gray images look much better than the Forma and sw dither images, both of which start to darken well before getting to outer surrounding black ring and have other artifacts.
Photos please.
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Old 02-05-2020, 01:00 AM   #72
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Photos please.
I'm not set up for that and it will be quite some time before I can spend any time on it.

There are any number of other people that can put the same images on their kindles and take pictures.
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Old 02-05-2020, 07:58 AM   #73
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I'm not set up for that and it will be quite some time before I can spend any time on it.

There are any number of other people that can put the same images on their kindles and take pictures.
I did the photo I took with my iPhone 6s camera. Came out just fine.
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Old 02-06-2020, 08:54 AM   #74
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Okay, turns out my PW2 is on a FW recent enough (5.9.7) to possibly be useful as a data point.

(And it's old enough that there's also no useful dithering implementations at the kernel/HW level, although I doubt those are actually used even on current devices anyway. In Kobo land, that'd be equivalent to Mk. 6 HW, but better ;p.).

In order:

* Forma gradient, full-color
* Forma gradient, grayscale
* Forma gradient, IM's 8x ordered dither
* full-color, but perfectly resized for the PW2 screen
* My usual full pipeline, so, error-diffusion dithering, perfectly resized for the PW2 screen

The TL;DR: being:

* It's using a slightly different grayscaling method than I do, as mentioned above, but that's not problematic, it turns out just fine.
* For unprocessed content, it applies a pretty nice dithering pattern. It's *almost* perfect:

Code:
  Colors: 26
  Histogram:
     12292: (0,0,0) #000000 gray(0)
      7380: (4369,4369,4369) #111111 gray(17)
      8292: (8738,8738,8738) #222222 gray(34)
     49061: (13107,13107,13107) #333333 gray(51)
     80568: (17476,17476,17476) #444444 gray(68)
    108476: (21845,21845,21845) #555555 gray(85)
    103656: (26214,26214,26214) #666666 gray(102)
     32704: (30583,30583,30583) #777777 gray(119)
     35050: (34952,34952,34952) #888888 gray(136)
     38577: (39321,39321,39321) #999999 gray(153)
     42695: (43690,43690,43690) #AAAAAA gray(170)
     47932: (48059,48059,48059) #BBBBBB gray(187)
     55561: (52428,52428,52428) #CCCCCC gray(204)
     61404: (56797,56797,56797) #DDDDDD gray(221)
     64547: (61166,61166,61166) #EEEEEE gray(238)
         4: (61423,61423,61423) #EFEFEF gray(239)
         6: (61680,61680,61680) #F0F0F0 gray(240)
        12: (61937,61937,61937) #F1F1F1 gray(241)
       993: (62194,62194,62194) #F2F2F2 gray(242)
         4: (63222,63222,63222) #F6F6F6 gray(246)
         1: (64250,64250,64250) #FAFAFA gray(250)
         8: (64507,64507,64507) #FBFBFB gray(251)
      2164: (64764,64764,64764) #FCFCFC gray(252)
      1841: (65021,65021,65021) #FDFDFD gray(253)
        14: (65278,65278,65278) #FEFEFE gray(254)
     22950: (65535,65535,65535) #FFFFFF gray(255)
* On the other hand, if your content is *already* dithered, horribleness ensue. Extra horribleness if there's a scaling pass needed on top ^^.
EDIT: Not entirely exact, see the following post .

----

Fair warning: As I've mentioned earlier, I'm not sure this has any bearings on real use-cases. Where it matters (i.e., the Cover view), the Kindle has always been doing a very good job of dithering the thumbnails (in fact, possibly with this very same algorithm). I consider Comics/Manga reading a non-issue, because eInk and 6", but regardless of my own preferences, I have no doubt it was also handling those use-cases just fine anyway.
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Old 02-06-2020, 09:07 AM   #75
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Posts: 9,979
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Join Date: Jun 2010
Location: Paris, France
Device: Kindle 2i, 3g, 4, 5w, (PW) & PW2; Kobo H2O & Forma
Oh, okay, turns out the horribleness is *NOT* directly related to dithering, but it's the (usual) Kindle's inability to deal with 16c PNGs properly.

If I apply the same workarounds as in the ScreenSavers hack (i.e., making it a 256c Gray PNG8 via -define png:color-type=0 -define png:bit-depth=8), it behaves just fine, and the dithering pass doesn't mangle my own dithering .

Code:
  Colors: 16
  Histogram:
     11815: (0,0,0) #000000 gray(0)
      7995: (4369,4369,4369) #111111 gray(17)
      5601: (8738,8738,8738) #222222 gray(34)
     10304: (13107,13107,13107) #333333 gray(51)
     12262: (17476,17476,17476) #444444 gray(68)
     78117: (21845,21845,21845) #555555 gray(85)
     91491: (26214,26214,26214) #666666 gray(102)
     98963: (30583,30583,30583) #777777 gray(119)
    109778: (34952,34952,34952) #888888 gray(136)
     51459: (39321,39321,39321) #999999 gray(153)
     43618: (43690,43690,43690) #AAAAAA gray(170)
     47427: (48059,48059,48059) #BBBBBB gray(187)
     55048: (52428,52428,52428) #CCCCCC gray(204)
     59253: (56797,56797,56797) #DDDDDD gray(221)
     65299: (61166,61166,61166) #EEEEEE gray(238)
     27762: (65535,65535,65535) #FFFFFF gray(255)
The only downside to this workaround is larger filesizes.

FWIW, when I mention "my usual pipeline", it's this: https://www.mobileread.com/forums/sh...1&postcount=17

Which is essentially a souped-up version of what the ScreenSavers hack does in cover mode (but with fancier scaling via EWA eliptical algorithms in linear space).

----

TL;DR: Kindles are (probably) Doing It Right (mostly), which we kind of knew already, and isn't much of a surprise .
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Last edited by NiLuJe; 02-06-2020 at 09:17 AM.
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