regarding vertical resolution 228 vs 192

[Aloan]

Sorry to ask this here! I did not find a specific place to... but this may be an easy question:
It´s regarding the Stella Emulator.
When I press F12 to take a screenshot it saves the picture to 160x228.
But I read on the net that 228 is the PAL resolution and so I wanted the picture to be taken

at a 160x192 resolution or actually play games at that resolution instead.
I went into the settings for NTSC is not even a word inside there (I did not find anything related to that)
Does anyone know how I could do so games play and pictures taken are all at 160x192? thanks

[Thomas Jentzsch]

Stella saves snapshots with some extra vertical lines, because the 192 NTSC display scanlines are not a fixed value. Many games use more scanlines. The 228 has nothing to do with PAL.

 

BTW: Pixel exact NTSC Screenshots are taken with 320x228 pixel (PAL 320x274). That's because of the odd aspect ratio of a 2600 pixel.

 

 

 

 

 

[+Andrew Davie]

To expand on this;  the visible horizontal resolution of 160 pixels is a hardware limitation. There are 228 "colour clocks" on a scanline but a scanline consists of 160 visible pixels, and 68 not-visible pixels (the horizontal blanking period on a TV).  Think of a "colour clock" as a unit of time, not a visible pixel. So a scanline really only has 160 pixel horizontal maximum, and takes 228 colour clocks of time to display.  Playfield graphics are a quarter of this resolution, only 40 playfield pixels wide.  But essentially you have visible width of 160 pixels.

The vertical resolution is different - this is not driven by hardware, but by software. It doesn't matter if the machine is PAL or NTSC; it is the game cartridge software that draws the screen and decides how many vertical lines of graphics there should be. The complete TV 'frame' consists of a standard 262 lines for NTSC, or 312 for PAL.  But these are standards, not mandates. A programmer can decide to increase or decrease the number of scanlines, and within limits a CRT TV will adjust the scanning frequency (#frames/second) to accomodate the new size.  Of those standard 262 or 312 lines, there are usually areas at the top and bottom of the visible graphics which are kept black. This is because TVs vary, and usually only 192 or so of the 262 lines (NTSC), or -- I forget how many for PAL -- are visible. Is it 228?  I think it might be, but the correspondence to colour clocks and horizontal resolution here would be purely coincidental.

Another way of thinking about this is:  when you set NTSC or PAL, you are only setting how the colours are displayed. You are not changing the resolution.  The resolution is hardwired.  Horizontally, 160 pixels visible, set by the hardware itself.  Vertically, a variable amount, set by the game software.

Hope that clears things up a bit. 

[+SpiceWare]

8 hours ago, Thomas Jentzsch said:

Stella saves snapshots with some extra vertical lines, because the 192 NTSC display scanlines are not a fixed value.

 

In this reply I checked out my games and the vertical screen size ranged from 182 for Draconian to 202 for Stay Frosty 2. All games except Draconian were greater than 192.