Re: coloured text distorted on 4k monitor
On 2020-08-04 19:48, Eyal Lebedinsky wrote:
On 2020-08-04 16:43, Tim via users wrote:
> Tim:
>>> You may want to play with aliasing controls for font rendering.
>
> Eyal Lebedinsky:
>> I need to look into this (fonts) but hoped the problem is elsewhere.
>
>>> Perhaps your monitor doesn't have the traditional RGB (red green
>>> blue) pixel grouping? It might be in BGR sequence (your photo
>>> looks like that from the defocused blurs on the green text).
>
>> I still do not see why placing an windows at an odd x is different
>> from an even position. Moving the image changes between these two
>> displays with each pixel shift.
>
> With fonts, at least, aliasing is used for sub-pixel rendering. In
> other words, they don't just render at the pixel level, they use
> portions of the adjacent pixels, too (we might regard one RGB sequence
> as one pixel, it can drive each individual R G & B pixel). If the
> renderer doesn't know the sequence the pixels are in, it could start to
> use non-adjacent pixels. And as you bump things minutely one way or
> the other, you may discover rendering flaws.
>
> The font aliasing trick for tiny fonts could also be done for other
> graphical drawing (fine lines, etc). I don't know whether Fedora does
> that.
>
>> BTW this is what the pixels look like:
>>
http://members.iinet.net.au/~eyaleb/attachments/20200801/dsc08774-part1.jpg
>> Looks like BGR left-to-right? Should that matter?
>
> It's kind of hard to tell, but looking at the grouping, with widest gap
> between two colours, it looks like green red blue GAP green red blue
Actually, looking half way down the image, checking for the dark vertical gaps,
the left side looks like GRB and the right side more like BGR. Mmm.
>> Still, using 'xmag' shows a nice text without any artifacts, so I
>> wonder if this is an issue with the actual monitor (TV) - assuming
>> xmag grabs pixels from the screen not knowing how they were painted
>> (e.g. a font renderer).
>
> As is often said, TV sets don't usually make great monitors
> (particularly with fine text). Apart from accuracy issues, they often
> have all kinds of processing trying to make real pictures look better
> than the TV can display without assistance, or to hide reception
> problems.
>
> If you have sharpening turned on, that tries to make a picture look
> sharper than it really is, and they rarely do that well. On some sets,
> the sharpening control is a boost-only control, where zero is
> unmodified. On other sets, it's a boost and cut control, where the
> middle position is unmodified, one end is artificially crispened, the
> opposite end is artificially softened.
>
> Some TVs actually have a different resolution than what you expect.
> They'll render up or down, so you won't get a 1:1 pixel representation.
> Putting them into a PC mode can help. Some sets go into an
> undocumented PC mode if you rename an input to PC.
>
> Even computer monitors can be awful at rendering tiny text. The goal
> of higher and higher resolution monitors is not so much at being able
> to render smaller and smaller text, but to better render normal text.
I am looking closer at the monitor. I created (gimp) a small test image of red
pixels on black bg. It is simply a run of r-b-r-b-r-b... pixels and the next
row if shifted one pixel.
http://members.iinet.net.au/~eyaleb/attachments/20200801/dots-red.jpg
I now display this image at 100% (1:1) and take a closeup picture. What I see is
nothing like what I expect.
The TV has a number of "picture modes". In standard mode:
http://members.iinet.net.au/~eyaleb/attachments/20200801/standard-mode.jpg
There is a row of all red pixels (should be alternating red and black), with a rather
dim
following row.
In PC mode:
http://members.iinet.net.au/~eyaleb/attachments/20200801/pc-mode.jpg
The red row is still missing the black pixels and the dim row is a bit brighter,
rather whitish.
I now suspect the TV more than anything else. I must find another to compare to...
Just to add another point. Viewing a b/w checkerboard pattern
http://members.iinet.net.au/~eyaleb/attachments/20200801/dots.jpg
I get a good result
http://members.iinet.net.au/~eyaleb/attachments/20200801/dsc08820.jpg
and it clearly shows a BGR pattern. So the TV can display a 4k pattern.
However there is a problem with colour patterns.
For a test I attached the TV to spare computer with a different os (ubuntu,
I use fedora), different video card (nvidia, I use onboard intel). Same problem.
Interestingly, ubuntu boots into 4096x2160 by default.
--
Eyal Lebedinsky (fedora(a)eyal.emu.id.au)
