Quote:
Originally Posted by lensmann
I'm a bit puzzled by this. Kobo's specifications say:
In the EU, that means they have to deliver a product which displays black-and-white content at 300 PPI. Section 18(1)(d) of the Consumer Rights Act 2022 says:
That's an Irish law, but it's based on EU directives and all EU countries will have similar provisions (as will the UK). It makes it quite clear that if a product is advertised as having 300 PPI, then the delivered product must have that functionality. It surely can't be that Kobo is acting in flagrant disregard of this law. There must be some sense in which the screen does in fact display black-and-white content at 300 PPI. |
The 300 dpi has been put in by marketing people. They will get in trouble, but only when people complain. It's not proactive.
Various TV and panel makers and MS did cause controversy over claims for PenTile displays and subpixel addressing such as Cleartype.
https://en.wikipedia.org/wiki/PenTile_matrix_family
With the increasing availability of HiDPI displays after 2012, subpixel rendering has become less necessary
https://en.wikipedia.org/wiki/ClearType
Originally all colour systems used either stripes or a wheel/drum. But beam indexed stripes in 1950s was a problem and the single gun CRT wasn't viable till the 1990s, but then made obsolte by Plasma and LCD. So in 1952 till Trititron the triad of dots and a shadowmask used.
Stripes came back with LCDs, but in the last 20 years many sub pixel layouts tried. ALL LCD planels, like mono eink are mono and higher resolution than the resulting display.
See
https://en.wikipedia.org/wiki/Pixel_geometry
Only has some options. Triton eink was R G B stripes, so a 300 dpi panel would give 100 dpi x 300 dpi.
The Kaleido is a pattern of pastel red, green and blue in a 2 x 2 layout. Pastel to improve brightness, so the 300 dpi is reduced to 150 dpi colour.
It's true that with a pure mono image or text you get a bit better than 150 dpi, but not a real 300 dpi. You can't switch off the printed colour dots.
Electronic cameras used to use either three sensors or stripes, then they changed to approximately a 2 x 2 cell.
See
https://en.wikipedia.org/wiki/Bayer_filter
If the sensor is 4000 x 3000 then the full colour resolution is 2000 x 1500 square pixels, unlike stripes which would be 4000 x 1000 or 1333 x 1500.
Any display filter works for a camera, and any camera filter works for a display, except the sensor is processed by software/HW and the display is "processed" by your eyes.
I don't know what exact layout Kaleido is, but since they quote 150 dpi colour for a 300 dpi panel, it's the rectangular (less than ideal) Bayer layout if the panel is the regular mono type. If they can offset each row of pixels alternately by 1/2 pixel (unlikely) then they can use the better delta layout:
https://en.wikipedia.org/wiki/Pixel_geometry
See also
Quote:
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The second common method uses a typical grey scale e paper display behind a transparent color layer. The color layer is a LCD based CFA. When displaying grey scale images the device runs at its native resolution, for instance, 300 pixels per inch (PPI). However, due to the CFA, the resolution of the device drops when displaying color images, say to 100 PPI.[35] When the image to be displayed consists of both a colored and a black and white section, for example when a book page comprises plain text as well as a color photo, some e book devices may display the photo at the reduced resolution while the text is at the normal resolution. As the CFA is LCD based, the CFA requires constant power to run and uses more energy.
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This is actually WRONG! The 300 dpi is lost due to the colour filter. The article also seems to suggest Triton (100 dpi, which is still 300 dpi on the other axis).
https://en.wikipedia.org/wiki/Color_...ay#E-paper_CFA
Also it's a CFA the same as used on an LCD. There is no LCD layer on any eink panel.
Kobo will be fine in the EU until someone brings a complaint.
It's true that black text on "white" paper will be better than a native 150 dpi panel like on DXG or other 9.7″ ereaders, but can't ever be as sharp as a 300 dpi mono panel without a printed colour pattern.
As with HiDPI displays, at a certain point a colour panel less than 300 dpi will look as good as mono 300 dpi, probably about 225 dpi, which would need a mono panel of about 450 dpi.
If you'd benefit from reading glasses and don't use them then the Libra Colour will look as good as the Libra2. But it's misleading to claim that a 300 dpi mono image/text on the Libra Colour is as sharp as the 300 dpi Libra 2. It's physically impossible.