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Forum 135

Tech Chat Aspect Ratio To Pixel

General Technical Discussion

Last Post by crustytv 1 year ago

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crustytv

(@crustytv)

Posts: 12242

Vrat Founder Admin

Topic starter

Hi, would anyone know the height and width in pixels for an image to correctly fit a 625-line 4:3 aspect ratio?

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Posted : 01/09/2023 1:33 pm

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Pixel Aspect ratio

Cathovisor

(@cathovisor)

Posts: 6556

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@crustytv Depends...

An "analogue" PAL picture is 702 x 576 pixels: 52µS active line @ 13.5MHz sample rate = 702.

A "digital" PAL picture is 720 x 576 pixels. Hence the little 'ears' on the Test Card which tell you whether or not the signal had analogue or digital blanking.

With square pixels, it'd be 768 x 576 pixels.

However... unlike HD, PAL pixels are NOT square. The consistent bit here is the 576, which is the number of active lines (and even then, there are only 575 active lines in analogue PAL)

I bet you wished you'd never asked now 😉

Posted : 01/09/2023 3:44 pm

crustytv

(@crustytv)

Posts: 12242

Vrat Founder Admin

Topic starter

Posted by: @cathovisor

↑

I bet you wished you'd never asked now 😉

Not at all Mike, I hoped you see this as I knew this was right smack in your field.

This explains why my 768X576 cards looked odd, using 720X576 looks spot on. Context; I'm testing all the test cards in anticipation of adding them to my BATC EPROMs, by using the Pi-Patgen to view, they all looked mildly squished using the first pixels sizing.

I did find some excellent online 4:3 calculators, but they all seemed to cover HD only, I gave up and thought why not ask here.

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Posted : 01/09/2023 3:58 pm