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
.
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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.