4:3 video scaling - Page 1
Forum section: electronics / projects

author: RyanG
author_rank: Regular Contributor
timestamp: September 11, 2018, 11:39:28 pm
content: I have a system that puts out a black and white video signal to be displayed on CRTs, which gets colorized by another board between the TVs and video input. I am going to remove the colorizing part. I am running out of parts and buying new CRTs costs more than buying a new LED TV. I can hook the B+W analog signal straight into some TVs and it kind of works, but other TVs need to have an RF modulator to get the picture on screen. The problem that exists in both situations is that the bottom of the picture gets cut off on the widescreen TVs. Also, without the RF modulator the TVs display the proper image, while still being cut off at the bottom, but say that there is no input. What would be the best way to fit the image to screen without having to convert the signal to another format then scaling on the TV since auto-scaling the signal doesn't work on component inputs? I have tried the different zoom levels and everything on the TVs I have here, but nothing works.

author: macboy
author_rank: Super Contributor
timestamp: September 12, 2018, 02:57:02 pm
content: All CRTs will overscan, so part of the active image area is always cut off on all sides. This is necessary for a few reasons including closed-captioning encoding which uses a few lines of the active image area but should not be displayed. Most HD displays have adjustable overscan, and can usually be adjusted to display more of an analog composite video signal than any CRT monitor would ever have displayed.Also check if your "system" properly observes the porch (inactive) areas of the video signal.Almost any old video tape recorder / VCR can be used as a video modulator since they usually have a composite video input and RF output.

author: drussell
author_rank: Super Contributor
timestamp: September 12, 2018, 05:10:11 pm
content: Quote from: macboy on September 12, 2018, 02:57:02 pmThat would be my suspicion, as well... Things like those bowling scoring systems often had signals that were only,ahem,"loosely based," shall we say, on the signal standards.It is quite likely that the non-conformant signal is what is confusing the newer TV inputs since, if anything, you should be seeingmoreof the total screen area of a proper signal than on a CRT.It might be possible to fairly easily invent some circuitry to modify the signal to have better behavior if a severe deviation from the norm can be ascertained from looking at the signal....

author: RyanG
author_rank: Regular Contributor
timestamp: September 13, 2018, 01:44:06 am
content: It is a bowling scoring system. I had a lot of help from someone here on the forums last year with fixing the CRTs, but I have 3 tubes that are about to be trash with only 2 replacements. I know that more are going to be on their way out soon. I can use the one board from the scoring system that overlays color onto the black and white and then puts out a RGBS signal. I can take that signal and put it through a board that converts CGA to VGA that people use in old arcade machines. I have set that up before but it requires one of the old boards, which I have many of those failing as well. I was just trying to find the simplest and hopefully cheapest way to do it, but $25 for one of the converter boards isn't that bad I guess as long as I can keep the old colorization boards working.

author: BrianHG
author_rank: Super Contributor
timestamp: September 13, 2018, 06:36:44 am
content: Quote from: macboy on September 12, 2018, 02:57:02 pmClosed captioning is not in the active display area of the video signal and it did not exist when CRTs came into existence, so this is obviously flawed logic.The first real reason for the overscan is that CRT picture tube aren't perfect rectangles. The corners are rounded, especially in old tubes which looked more like ovals than rectangles. The overscan allows the image to make it to the edge of the mid vertical/horizontal of the CRT tube, while, the outer corners are off the edge of the tube. If you wanted to see the four outer corners of the picture, you would have to shrink the image to a point where there would be a black border all around the image. And yes, with newer modern video signals, maybe along the top, a 1 line digital B&W bar code for closed captioned text and 1 or 2 line thick color bars, + other occasional digital data, however, this was not the purpose of the overscan developed in the 1927.The second reason is temperature and age drift of the electronics driving the 'yoke' in back of the CRT projecting the raster/image. On a cooler day, or as the TV warms up, the picture may be a little smaller and or shifted off center slightly until the temperature of all the analog electronics warms up. This would be annoying and considered a broken TV if every time you turn on the power, there would be a black border on one or more sides of the picture.The third reason is that the analog studio video mixing gear, when switching between 2 camera, or a video them camera source, left a random small border on either side of the image as the analog switch gate was never perfectly timed to the edge under many circumstances and before all digital studio mixing hardware came into play, the overscan hid quite a bit of few pixel fat/wide, thin line the entire vertical height of the image, garbage along the left and/or right borders.

author: drussell
author_rank: Super Contributor
timestamp: September 13, 2018, 11:13:28 am
content: Quote from: BrianHG on September 13, 2018, 06:36:44 amOld, analog style CC absolutelyisin the actual, active video data part of the signal. It is on line 21 and allows two languages, one each on the even and odd field. You can easily see it visually encoded with white bars flashing across the top of the image when you digitize an incoming CC'd signal into a video capture card or any other kind of full-signal display that doesn't intentionally hide it. If you convert a signal to run to a non-overscanned (say, computer monitor, for example, CRT or otherwise) you will see it. The reason you don't see it on the typical "flat screen" TV which is actually set to show the whole image is that it is being decoded and hidden by the video processing. On a CRT it was off the top of the screen, though on some CRT TVs (especially those that were built before CC was mandatory) you can see it if you decrease the vertical height so the entire picture fits on the screen.QuoteIndeed. They were even initially all completelyround, of course...Up until 1950, virtually every CRT was round. By the mid-1950s, virtually every TV CRT manufactured was rectangular because as soon as they got the manufacturing right, rectangular took over since it had always been obvious that a rectangular picture on a round screen was sub-optimal at best.Then when color CRTs appeared with RCA's introduction of the 15GP22 in '53-54, it was back to round tubes due to their more forgiving construction. The 15GP22 produced an excellent picture, although it was a bit dim but was a nightmare to build. This was mostly because RCA made all the parts interchangeable, any shadow mask could be mated to any screen and then joined to the metal funnel, so all parts had to be exact. Precise alignment was critical. It was Norm Fyler, over at CBS-Hytron that figured out the lighthouse method of depositing the phosphors using the actual shadow mask as a guide that with some refinement, was essentially the method that was used to the end of color CRT production.All color TV CRTs were round as screens got bigger, up to the various 21 inch tubes like the 21AXP22, 21CYP22, 21FJP22 and 21FBP22, bringing advancements like the focus mask (another one that Norm Fyler advanced with his UMF system) through to1964 (!!!)Westinghouse had demonstrated some rectangular color tubes and even briefly commercially produced a few 22EP22 tubes in very limited numbers, used in a Westinghouse set, for less than a year in '56-57 but it wasWAYto difficult and expensive (and slow! with a 24 hour pumpdown!) to build so was quickly abandoned. Commercially available rectangular screens didn't come around until RCA debuted the 25AP22 in 1964, finally bringing a "livingroom-sized" rectangular screen to market. This then trickled down to the smaller, less expensive tubes over the next few years,15 yearsafter B&W went all-rectangular!Other than the fact that the CC info actuallyisin the "viewable" video data portion of the signal, (even though you can't usually see it) I agree with pretty much everything else you said about overscan.

author: drussell
author_rank: Super Contributor
timestamp: September 13, 2018, 11:21:11 am
content: Quote from: RyanG on September 13, 2018, 01:44:06 amWhat model of tube are in your system's display chassis?

author: BrianHG
author_rank: Super Contributor
timestamp: September 13, 2018, 11:02:20 pm
content: Quote from: drussell on September 13, 2018, 11:13:28 amThe only thing about rectangle picture tubes, is they are still not truly rectangle. Even the modern attached studio screen, to correct the warp of the glass for a visual square display, they still have the corners off the display, see the image below.As for the line 21 test, funny, when I built my scaler, when I capture 240 + 240 (480i) lines on each field, there is no closed captioning text. Now, if I grab the original full 482i or weird 484i, yes, they appear, and in older raw camera footage, There is actual picture on these extra lines as well as a half line (starts at left of image until mid screen) at the bottom of the image.

author: BrianHG
author_rank: Super Contributor
timestamp: September 13, 2018, 11:09:39 pm
content: Quote from: RyanG on September 11, 2018, 11:39:28 pmYour video source may be 240p, which a lot of TVs aren't tested on to work properly with. I know you don't want to spend, but, there exist up-sampler/scaler boxes designed for old video game consoles which used 240p, some which support RGB input, which may help you with this problem. These boxes would allow you to use any cheap computer LCD monitors which show the full overscan. Modern TVs work as well...This might give you full quality for what you want to do:http://retrorgb.com/upscalers.html

author: RyanG
author_rank: Regular Contributor
timestamp: September 13, 2018, 11:36:00 pm
content: The tubes we have are 27" Zenith from around 1993.I've gotten the video onto a flat screen using one of these. It looks great, but I don't know how reliable those will be for the long term.https://www.ebay.com/itm/Arcade-Game-RGB-CGA-EGA-YUV-to-VGA-HD-Video-Converter-Board-HD9800-GBS8200/311759236377?epid=775682364&hash=item48964c6d19:g:fa4AAOSwEzxYZiQo

author: BrianHG
author_rank: Super Contributor
timestamp: September 14, 2018, 01:47:38 am
content: Quote from: RyanG on September 13, 2018, 11:36:00 pmWhen you say reliable, you mean availability... If you were to clone that board, it would cost you around 3x as much to build your own.With the avid old school console video games and Amiga fans out there which also used 240p and 480i RGB, such boards will be available for a good decade.

author: RyanG
author_rank: Regular Contributor
timestamp: September 14, 2018, 04:23:18 am
content: No, I meant reliable. The availability of those boards is fairly high, but I don't know if all sources are good quality.

author: BrianHG
author_rank: Super Contributor
timestamp: September 14, 2018, 05:06:54 am
content: Quote from: RyanG on September 14, 2018, 04:23:18 amYou can always design your own. You might even be able to pull it off with an Altera Max 10 PLD, Analog devices ADC, crystal, MCU to drive the I2C for the ADC, and a resistor dac VGA output, no ram needed for strict line doubling from 240p to 480p as there is already enough memory inside the Max 10 to do that. This is still however 30-40$ in parts and a PCB + assembly.As for those boards, we are talking about around 75 and 100 Mhz max on the PCB, probably only 4 layers, so, any junk will do. There only appears to be QFP and TSSOP packaged IC, so you don't need to worry about hidden BGA balls not being soldered properly. Your biggest worry here is the SMD soldering quality as this PCB isn't a power hungry above 15 watt device, like a 25-50 watt device with 1Ghz ram bus and BGA ICs all over the place with a circuit board which require impedance control testing before manufacturing, a full boot OS with file system, and networking, or, USB connected devices.Your biggest worries is static discharge coming into the VGA connector, however, once installed, if you keep the monitor always connected, this shouldn't be a problem due to the shielded low impedance connection. The RGB input sampling ADC is an ADC specifically designed for video and usually has the analog inputs protected as well as having series DC filter caps.Note that the video input IC on this board is most likely the same analog input IC used in many computer LCD screens, just running at a lower frequency.Also, some 16$ versions at eBay have 1 additional populated IC next to the VGA output, though, it may just be the example photo of the device.