Forma How many shades of grayscale does the Forma have?

[droopy]

How many shades of black/grayscale does the Forma have?

White = is one color
Black = another color
How many levels of gray are there in between completely black and completely white?

I need this info to figure out, when I convert full-color comic books or images (for the purpose of saving space on my forma), what number to use in the blank for "maximum colors".

Thanks!

[DomesticExtremis]

Can't say for the Forma, but experiments I did a long time ago on a Kobo Mini indicated that 16 levels of grey could be displayed though not necessarily discerned by the eye.
There is a fairly narrow contrast range on e-Ink screens, though it will improve with a frontlight.

[droopy]

DomesticExtremis, thanks for your quick reply.

[NiLuJe]

16 shades of gray, with an even stride of 0x11 (i.e., 0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88, 0x99, 0xAA, 0xBB, 0xCC, 0xDD, 0xEE, 0xFF), like every B&W eInk screen since the Pearl days.

[rashkae]

One thing I'll add, the Kobo Forma, (and indeed, every model of Kobo over the past 5 years, excluding the Aura One.) does a *really* good job of dithering with cbz files. I would not bother downscaling the colour at all, or at most, reduce to greyscale to reduce file size.

I exclude the Aura One because, for some reason, even though they all have the same firmware, I can clearly see the dithering pattern with the naked eye on that one. Not sure if I could get better results with by downscaling the colours myself, but it still looks great for most B&W Content.

[NiLuJe]

@rashkae: That's because the Forma (and other Mk. 7 devices) support hardware dithering, and it's indeed pretty decent (still slightly more obvious than a good 8x8 matrix (or a good error diffusion algo), but, pretty decent, and essentially free, which pretty much trumps any other concerns given how serviceable it is). Nickel's own isn't half-bad, but is hobbled by various legacy reasons, a visible consequence of that being a more obvious pattern.

[rashkae]

Originally Posted by NiLuJe

@rashkae: That's because the Forma (and other Mk. 7 devices) support hardware dithering, and it's indeed pretty decent (still slightly more obvious than a good 8x8 matrix (or a good error diffusion algo), but, pretty decent, and essentially free, which pretty much trumps any other concerns given how serviceable it is). Nickel's own isn't half-bad, but is hobbled by various legacy reasons, a visible consequence of that being a more obvious pattern.

The strange thing though.. both my Mark 5 H20, (I no longer have, so can't compare with latest firmware) and Mark 6 H20 do a better job of invisibly dithering than the Aura One,, even though they are lower resolution devices... and I would say, they are also both better than the 7th Gen Clara HD... (The Clara HD has this weird effect of creating diagonal bands of different shading on high resolution images, that leaves a faint but visible pattern.)

[NiLuJe]

@rashkae: I was going to say that one can play with the hardware dithering settings and/or input to make the pattern more obvious, and in particular thanks to how processing is highly vectorized, that can translate in visible, wide vertical stripes .

(You may be talking about much narrower vertical "stripy" patterns, though, and that would just be the pattern induced by the matrix).

If you have a Mk. 7 on hand, you can switch between HW & SW dithering in KOReader. Except we're using the kickass matrix ported from ImageMagick, so it kinda rocks .

----

Also keep in mind that dithering patterns have an extremely adverse effect on eInk ghosting, in that they basically feed each-other in a loop, so you may want to take that into account when making comparisons (i.e., start from a flash to white).

[JSWolf]

Kobo's software dithering is better then Amazon's.

[rashkae]

Originally Posted by JSWolf

Kobo's software dithering is better then Amazon's.

Hilariously untrue (especially for your beloved epubs) but at least it doesn't look horrible anymore, and the large forma screen more than makes up for it

[rashkae]

Originally Posted by NiLuJe

@rashkae: I was going to say that one can play with the hardware dithering settings and/or input to make the pattern more obvious, and in particular thanks to how processing is highly vectorized, that can translate in visible, wide vertical stripes .

You're right.. they are vertical.. I don't know why I was thinking diagonal.

The matrix is only visible to me, without artificial magnification, on the H20 2nd edition.. But I have to *really* try.

[NiLuJe]

Yeah, for devices with no HW dithering, you can take a screenshot and look at it on an LCD screen, that'll preserve Nickel's funky pattern, and it'll likely be much more obvious there than on eInk.

(And by "screenshot", I mean ideally an fbgrab, because Nickel's screenshot feature used to do extra funky stuff on some devices. This *may* no longer be the case, though, because why would I bother with that clunky feature when I can play with fbgrab over CLI? ;p [meaning I haven't tried it in over two years]).

But HW dithering doesn't affect the fb content, so, you'll only be able to eyeball it the old fashioned way .