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Re: Optimal Flatscreen monitors for QL and Q68

Posted: Mon Apr 15, 2019 1:17 pm
by Peter
janbredenbeek wrote:If the aspect ratio was indeed 4:3, the resolution would be 512x384, not 512x256.

I meant the actual screen aspect ratio, not pixel shape. Most CRT screens were about 4:3, and that determined the historic QL look - which the Q68 reproduces in the QL modes.
QL pixels were knowingly designed non-rectangular - historic software took this into account, so the actual look of pictures, characters etc. was such that it appeared normal when displayed on 4:3 screens.

janbredenbeek wrote:When using the Q68 on a 4:3 screen in QL-style MODE 4, the picture looks vertically stretched because the pixels are square while the width/height resolution ratio is 2:1.

Not for screens that were designed for the original QL. They were made for non-rectangular pixels, so the Q68 provides the historic QL look in the respective modes.
A screen with 2:1 would squeeze the picture vertically, compared to what you actually saw on most monitors from 1984 to 1999.

janbredenbeek wrote:On widescreen (16:9 or 16:10) monitors, the 512x256 and 1024x512 modes will look more natural because their aspect ratio comes closer to the original 1.48 ratio than on a 4:3 screen.

You talk about modern software designed for rectangular pixels here. If screens were designed for the original QL, they will not look natural. Classic QL software was never made for rectangular pixels.
Fortunately, the Q68 provides modes for both rectangular (modern) and QL-shape (historic) pixels, so there is a choice.

Re: Optimal Flatscreen monitors for QL and Q68

Posted: Mon Apr 15, 2019 3:37 pm
by janbredenbeek
Peter wrote:
janbredenbeek wrote:If the aspect ratio was indeed 4:3, the resolution would be 512x384, not 512x256.

I meant the actual screen aspect ratio, not pixel shape. Most CRT screens were about 4:3, and that determined the historic QL look - which the Q68 reproduces in the QL modes.
QL pixels were knowingly designed non-rectangular - historic software took this into account, so the actual look of pictures, characters etc. was such that it appeared normal when displayed on 4:3 screens.

It's best demonstrated by issuing the command CIRCLE 50,50,50 in S*BASIC. On the standard QL with original CRT monitor, this should look like a circle. The graphics coordinate system was designed in such a way that the scale in horizontal direction is the same as in vertical direction. Thus a horizontal line of 50 units would produce a line of the same length as a vertical line of 50 units - measured in millimeters, not pixels!
In reality, the horizontal scale of this system measured in pixels is 1.355 times the vertical scale, which is demonstrated by issuing the same CIRCLE 50,50,50 command on a PC emulator with 'square pixel' screen resolution. The circle then suddenly looks like a horizontally stretched ellipse! (if you type CIRCLE 50,50,50,1/1.355,0 you should get a perfect circle again).
Thus, the pixels of the original QL's 512x256 screen are 1.355 times as high as they are wide. Combined with the 2:1 ratio of the 512x256 resolution, the aspect ratio of the QL screen will then be 2/1.355 = about 1.476. This is wider than 4/3 due to the overscan.
Peter wrote:
janbredenbeek wrote:When using the Q68 on a 4:3 screen in QL-style MODE 4, the picture looks vertically stretched because the pixels are square while the width/height resolution ratio is 2:1

Not for screens that were designed for the original QL. They were made for non-rectangular pixels, so the Q68 provides the historic QL look in the respective modes.
A screen with 2:1 would squeeze the picture vertically, compared to what you actually saw on most monitors from 1984 to 1999.

But the Q68 has 1024x768 output and no horizontal overscan like the original QL. On a 4:3 flatscreen monitor, the aspect ratio will be 4/3. On a 16:9 or 16:10 monitor, the aspect ratio will be 16/9 or 16/10 as the monitor will stretch the 1024x768 to fit in the whole screen (unless you tell it not to do so).
Fortunately, the Q68 provides modes for both rectangular (modern) and QL-shape (historic) pixels, so there is a choice.

I'm quite accustomed now to the 'square pixel' resolutions from emulators and Q68 512x384 and 1024x768 modes, though they look somewhat stretched compared to the original QL screen (which I think was a bit squeezed horizontally by the geometry controls of my 1980's monitor to make the 512x256 fit in 4:3...).

Jan.

Re: Optimal Flatscreen monitors for QL and Q68

Posted: Mon Apr 15, 2019 7:28 pm
by Peter
janbredenbeek wrote:But the Q68 has 1024x768 output and no horizontal overscan like the original QL. On a 4:3 flatscreen monitor, the aspect ratio will be 4/3.

I still don't quite understand what you mean. In the QL modes, the Q68 creates rectangular "QL pixels" that are 2x3 screen pixels, so the complete 4:3 flatscreen area is used.
I assume most CRT monitors used with the QL were also 4:3 in geometry - and the picture also filled the whole screen, if correctly adjusted.
Hence a circle command in QDOS/Minerva delivers the same circle on Q68 with 1024x768 flatscreen as the QL did on a CRT.

What should be the difference in what the user sees?

Do you mean to say that historic CRT monitors used with the QL were not exactly 4:3 in screen size?

(I'm just using 4:3 as rule of thumb for CRTs, not as exact measure for every individual model.)

Re: Optimal Flatscreen monitors for QL and Q68

Posted: Tue Apr 16, 2019 4:12 pm
by janbredenbeek
Hi Peter,
Peter wrote:I still don't quite understand what you mean. In the QL modes, the Q68 creates rectangular "QL pixels" that are 2x3 screen pixels, so the complete 4:3 flatscreen area is used.
I assume most CRT monitors used with the QL were also 4:3 in geometry - and the picture also filled the whole screen, if correctly adjusted.
Hence a circle command in QDOS/Minerva delivers the same circle on Q68 with 1024x768 flatscreen as the QL did on a CRT.

I can't exactly verify this as the flatscreen I use for the Q68 has 1280x1024 resolution and upscales the 1024x768 display from the Q68. 1280/1024 is 5:4 (assuming square pixels) or 1.25 aspect ratio.
The circle I get in QL MODE 4 on the Q68 is squeezed horizontally, I guess it will be round again when I give it eccentricity 1.6/1.355 (1.6 comes from 2 divided by 1.25; 1.355 is the standard pixel height/width ratio used by the graphics system). On SMSQ/E I could just set PX.ASPRT in the CON driver definition block to 1.6 to get circles again.
Do you mean to say that historic CRT monitors used with the QL were not exactly 4:3 in screen size?

I have to dig up one from my attic to test this. Perhaps an idea for the coming Easter holidays ;)

Jan.

Re: Optimal Flatscreen monitors for QL and Q68

Posted: Tue Apr 16, 2019 7:24 pm
by Nasta
That's a rather complex discussion.

The QL uses a 'fake progressive' timing close to the PAL spec with some liberties which never the less work fine on PAL compatible TVs and monitors.
This format has 640 pixels per line, and 312 lines, which includes all invisible portions of the scan.
Each line takes 64us to display and out of this, the standard guarantees 48us of video to be visible on the screen. However, the QL uses 51.1us, so in theory, only 480 out of 512 total pixels in mode 4 will be visible on a CRT TV. Since CRTs are not exactly rectangular and had some distortion at the edges, the visible 480 pixels were always kept a slight distance from the corners and edges, so depending on the TV, some of the 32 'extra' pixels in each line were still visible on TVs.
Not all of the lines are visible either. Out of the 312, about 288 are visible from absolute top to bottom of the screen. Again, the typical CRT was not rectangular (unless it was a Trinitron...) so several lines could be clipped by the rounded top and bottom edge. So, the screen was too wide to display on a 4:3 CRT but also did not use the entire height of the 4:3 CRT. However, TVs in general were set up to that the well reproduced area of the screen was about 480 x 240 in QL pixels, which is still 2:1, though since about the same border was put on the CRT in centimeters on all sides, and the screen is wider than it is tall, the same number of cm of border is less of a percentage in the horizontal direction. Because of this the TV picture shows very slightly squashed circles - usually the difference is imperceptible, since a regular TV screen geometry is not that precise to begin with.

On QL specific monitors, the picture was made narrower so that all 512 pixels fitted the screen and also all visible lines. So, on modern LCD monitors, the best fit will be double wide and triple high pixels on a 1024x768 LCD panel, and like all LCDs no border.

1280x1024 LCD panels have square pixels and a 5:4 aspect ratio. This was originally a 'workstation' resolution and was intended to be displayed with square pixels, which was done in two ways, depending on the workstation monitor OEM execution of the standard - one was a real 5:4 aspect ratio screen, and the other was a regular 4:3 screen with unused borders on the side. The fun part of this story is that both actually used the same 4:3 screen and unused border, just in the first case the plastic surrounding the screen was extended to cover the unused portion to the left and right, and the whole design of the front was adjusted so it was not perceptible and looked like a 5:4 aspect ratio CRT :)
At one point I had a SUN and Tektronix 19" trinitron monitor side by side and noticed the picture was exactly the same size, just the SUN had a narrower case, and guessed (correctly) that it would have been FAR too expensive to produce two completely different CRTs (even with the prices charged for these monitors back then!). I just about laughed my head off when I opened the monitors and found the exact same thing just with a different plastic case, covering the unused portion of the screen front in case of the SUN monitor, and the left and right edges of the glass tube being closer to the insides of the plastic case.
Upgrade your SUN workstation monitor to 1366x1024 by cutting plastic :P
(Well... I know Apple II users who upgraded their floppy drives from 36 tracks to 40 using a file to file off the head end stop, so perhaps there is precedent)

Unfortunately, 5:4 LCD screens that have an 'maintain aspect ratio' option were very rare, most simply stretch the picture to full screen, resulting in a vertically elongated picture. The aspect ratio option was only popular for a short time when 16:9 or 16:10 aspect ratio LCDs became available as their native resolutions were not commonly supported back then, but today it's stretch, no matter which way, to fill the screen. And you are lucky if it even recognizes any of the lower VESA modes properly except 720x400 text to get to a PC BIOS screen :/