03-05-2019, 06:10 AM
As Frank implies, when you're working with interlaced standards, the vertical counters are normally counting half lines. So on 405 there are 405 half lines per field. You can get some very strange effects if you inadvertantly count an even number of half lines.
This doesn't apply to Hedghog which only has line stores but if you're working with a framestore it all gets more complicated. You have various ways of organising the memory. You can store the lines in vertical order. That means that if you read the memory linearly the result won't be interlaced. So you have to increment the vertical address by 2 lines per line to get interlace. Or you can store lines in temporal order, efffectively 2 blocks of memeory, one for each field. Both methods have pros and cons.
This doesn't apply to Hedghog which only has line stores but if you're working with a framestore it all gets more complicated. You have various ways of organising the memory. You can store the lines in vertical order. That means that if you read the memory linearly the result won't be interlaced. So you have to increment the vertical address by 2 lines per line to get interlace. Or you can store lines in temporal order, efffectively 2 blocks of memeory, one for each field. Both methods have pros and cons.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
