Porta Pattern - Videokarma.org TV - Video

jeyurkon · #1 05-15-2010, 03:48 PM

I picked up a Porta Pattern Video Test Pattern Generator from a store on eBay. It appears to be a re-branded Photoshare7, which you can get for about 1/5 the price from Amazon.

It does come with a plethora of test patterns and reference information about the various tests and signal standards.

Whether it's worth the extra cost for those features would be a personal decision.

jeyurkon · #2 05-16-2010, 04:12 PM

After having a chance to play around with the Porta Pattern generator, I would advise against purchasing one.

The patterns end up shifted to the right about 10% of the screen. The resolution is less than specified, at least for the 4:3 aspect ratio it's much less than my Pioneer videodisc player.

I also tried it with my Mitsubishi DLP in 16:9 mode and the patterns are still shifted.

John

bandersen · #3 05-17-2010, 03:52 PM

Thanks for the info. I'd seen those a few times and wondered how well they worked.

tom_vk · #4 10-31-2011, 01:46 AM

I've just tested one of these.

It doesn't seem to generate 720 by 480. It generates 703 by 470 by cropping all images.

The Test patterns are badly offset to the right as well (as already observed). They are also "squeezed horizontally" by about 10% due to a fast pixel clock, so there's only video for 90% of the scan line "active time". This also means they're not "square" and so the circles aren't round either. Even on its internal screen the "circles" are 103 by 84mm.

It doesn't generate 480 lines of vertical resolution, but filters down to 240 lines (235 with cropping). This is probably a "flicker filter" for CRT-based televisions.

The Test Pattern bitmaps have lost many of their high frequency components during conversion. The 720 pixel horizontal resolution limits the horizontal frequencies that can be generated too.

The Test Patterns only display 480 out of 576 lines when in PAL mode as the patterns haven't been "stretched" to fit. In PAL mode, Test Pattern "Circles" measure 43cm by 28cm!

There's a strange "noise burst" of what seems to be Chroma at the start of the horizontal active time. See it here:

http://www.itworks.com/products/port...n/DSC00735.JPG

tom_vk · #5 11-20-2011, 04:57 PM

The Test Patterns only work properly (all other faults considered) on old 4:3 television sets. On all widescreen (16:9 - everything made in the last 5 to 10 years) sets the test patterns are badly stretched.