Better anti-aliasing

[Bert Freudenberg]

On 25.04.2008, at 16:02, Paul Fox wrote:

> bert wrote:
>>
>> On 25.04.2008, at 15:07, Paul Fox wrote:
>>> unlike a traditional display, every pixel has a single color.
>>> given this, it seems wrong to talk about the "red channel of the
>>> first pixel".  you either use some of that pixel, or you don't.
>>> in effect, the display is implementing sub-(full-color-)pixel
>>> rendering all by itself.  (which i think is what bert was saying,
>>> but the "channel" thing confused me.)
>>
>> In the display memory (a.k.a. framebuffer), each pixel has a red  
>> and a
>> green and a blue value. I called these components "channel", which is
>> not entirely correct. Still, the DCON selects only the red component
>> of a framebuffer pixel to be displayed for a red physical pixel, the
>
> ah!  the missing piece.  thanks.  i was so focused on the display  
> itself
> that i'd never worked backwards to think about it from the
> perspective of the framebuffer.

great :)

>> value of the green and blue components do not matter. If the 5-tap
>> antialising filter is enabled, then the 4 adjacent pixel's red
>> components are averaged, and mixed with the center pixel's red
>> component. Again, the green and blue components are ignored, hence I
>> spoke of "selecting". Makes sense?
>
> yes.
>
>>
>>> with the backlight off, this doesn't matter -- all pixels are the
>>> same color anyway.  but with the backlight on in monochrome mode,
>>> you see a lot of color in single-pixel-width lines.  if the line
>>> is perfectly aligned with the diagonal of the pixels, it will be
>>> completely colored (i just tried it), but mostly you just get a
>>> lesser or stronger fringing effect.
>>>
>>> for backlit ebook mode, this might not matter so much, since ebooks
>>> might not have a lot of diagonal single-pixel-width lines, but the
>>> effect is definitely there.
>>
>>
>> But it is greatly diminished by the antialiasing hardware filter. See
>> if reading
>>
>> 	http://wiki.laptop.org/go/Display
>>
>> clears things up. With "selecting the red channel" I meant the DCON
>> "swizzling" as described on that page.
>
> yes, i see.
>
> since this sub-topic came up in the context of using the
> backlight in e-book (monochrome) mode, are you saying that the
> unimplemented "swizzled not antialiased" mode would be better
> than either of the two modes currently available ("monochrome"
> and "swizzled antialiased")?


Oh, I was not suggesting one mode was better than another. Ben brought  
up the "better aa" discussion again. The "swizzled not aa" mode would  
be needed to experiment in that direction. IMHO the display is great  
as it is, I find text highly readable even in color with aa.

That said, the available monochrome-with-backlight-no-aa mode is  
slightly more crisp, so for an ebook reader some people might prefer  
it. You get more visible color fringes though, and for my taste the  
edges are too jagged. But then I am used to Apple's font antialiasing  
which others find too blurry, they prefer FreeType's and ClearType's  
crispness. I could counter that with Alvy-Ray's "A Pixel Is NOT A  
Little Square" chanting which would get us soon into the whole Nyquist– 
Shannon sampling theory discussion, but I'll stop here ;)

- Bert -