analog video effect - Page 1
Forum section: electronics / projects

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: November 20, 2019, 02:50:53 am
content: What was it called when the luminance was discretized? I think it made things look like paint by numbers larger areas of equal luminance.Seems to me there was a project in a 1980s Radio Electronics for an analog video effects box.

author: Someone
author_rank: Super Contributor
timestamp: November 20, 2019, 03:45:06 am
content: The keyword is probably "coring" it has been applied in both analog and digital domains.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 20, 2019, 03:46:12 am
content: Dunno for video, but "posterize" is the relevant effect in Paint Shop.Tim

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: November 20, 2019, 10:46:21 am
content: Quote from: T3sl4co1l on November 20, 2019, 03:46:12 amAwesome, that's the word I was trying to remember! As in "looks like a poster" I guess.Now to find out how that was achieved in the analog domain, a flash converter with variable bit width fed back to a DA converter?

author: mikerj
author_rank: Super Contributor
timestamp: November 20, 2019, 05:36:10 pm
content: You could do this pretty easily with a bunch of comparators.

author: SiliconWizard
author_rank: Super Contributor
timestamp: November 20, 2019, 05:49:59 pm
content: Either way, wouldn't you need some kind of memory to deal with 2D blocks? Averaging luminance over a certain period on a given scan line (thus over a certain width) is easy, but averaging it over a certain square area? Can you do it without memory?

author: macboy
author_rank: Super Contributor
timestamp: November 20, 2019, 06:03:54 pm
content: Quote from: SiliconWizard on November 20, 2019, 05:49:59 pmYou misunderstand, there is no averaging involved. It is just reducing levels of quantization to some small number of levels. It's something like having a 1-digit voltmeter that can only display "0" through "9" instead of "0.000" through "9.999".

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: November 20, 2019, 11:49:41 pm
content: Quote from: mikerj on November 20, 2019, 05:36:10 pmThat's the idea I suppose, create a bunch of reference voltages for the bank of comparators with a bit of hysteresis, and then re-create the video signal. The usual analog video problems need to be solved, clamping to the black level to leave the syncs untouched and delaying the chroma so it still lines up with the processed luminance.I guess, it's just idle speculation right now.

author: floobydust
author_rank: Super Contributor
timestamp: November 21, 2019, 12:27:14 am
content: See Radio Electronics Sept/Oct. 1987 Video-Effects Generator, entirely analog.Posterizationis done with a MC3430 quad high-speed comparator.edit: Introhttps://americanradiohistory.com/Archive-Radio-Electronics/80s/1987/Radio-Electronics-1987-09.pdfSchematic etc.https://archive.org/details/radio_electronics_1987-10/page/n45

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: November 21, 2019, 12:32:16 am
content: *that's* the thing! Awesome. Thanks!

author: vk6zgo
author_rank: Super Contributor
timestamp: November 21, 2019, 01:13:42 am
content: Quote from: Alex Eisenhut on November 20, 2019, 11:49:41 pmHardly major problems-- it was done all the time, back in the day!Quote

author: SiliconWizard
author_rank: Super Contributor
timestamp: November 21, 2019, 08:38:46 pm
content: Quote from: macboy on November 20, 2019, 06:03:54 pmWell, I was actually thinking about a bit fancier "posterization" effect (I happen to have worked on one a long time ago). Just quantizing the signal "pixel" by "pixel" doesn't look very good. By "posterization", I was understanding any effect that would quantize luminance (or colors, depends on the effect you're after) to a limited number of levels, which is exactly what you said above. But there are various ways of doing it, some that will look much "nicer", and involving averaging over a certain area around every pixel (or otherwise some other kind of filtering), thus my question. You can discretize luminance with a much better looking effect.Now if we are talking about basic quantization pixel by pixel without anything fancier, obviously I agree, you don't need any memory or any kind of filtering.And for this, yes, once you have a sync detection circuit, that can be done with a relatively simple analog front-end and a flash ADC (+DAC, the DAC can be just a few resistors though, not that accuracy is probably a concern here.)Obviously discrete comparators can also be used; their number will quickly add up though unless you're after a very small number of levels (admittedly, 16 levels for instance, would "only" require 4 ICs using quad comparators). Flash ADCs are actually made of fast comparators (plus some logic).https://en.wikipedia.org/wiki/Flash_ADCI'm trying to think of a purely analog way of doing this. Sure you can argue that using comparators would be purely analog. I wonder if we can find a way of getting a similar "posterization" effect without comparators, with a reduced part count, using some clever trick.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: November 22, 2019, 02:16:43 am
content: "using some clever trick."Attenuate video signal, pass through a stack of Josephson junctions, amplify?

author: jhpadjustable
author_rank: Frequent Contributor
timestamp: November 22, 2019, 04:16:25 am
content: Quote from: SiliconWizard on November 21, 2019, 08:38:46 pmIs it cheating if I use a diff pair as a comparator? I offer this unoptimized brute-force design, just a set of voltage buffers and a flash ADC and DAC without the encoding/decoding nonsense. It's cost-reduced if not part-reduced. Three resistors and one CA3046-type monolithic transistor ensemble make one stage. n stages provide n+1 levels of brightness. The capacitor represents a cheap level shifter. Color and sync sold separately.If you had a fast sawtooth generator, one fast comparator (or equivalent), one DFF, and one fast edge-triggered sample/hold, you could clock the DFF n times faster than the sawtooth to get n (n+1?) levels of posterization.