Dithering on the Sega Genesis with Composite Video

if you want to play the Sega Genesis the way it was meant to be played you should use composite video but why RGB output looks amazing especially on the Genesis why would you even consider using composite video the answer is dithering I feel that this subject is lost due to the recent surge of interest in professional video monitors and upscaling devices so let's talk about it by making use of detailed pixel patterns in its graphics the Sega Genesis used dithering to simulate transparency and create additional colors when the consul's video signal was displayed on a television this was achieved by leaning heavily upon the degraded image fidelity found when using a composite video signal when you use a superior quality signal such as RGB the dithering process is incomplete as the compromising of the details so to speak is no longer performed many feel that the overall image improvement gained from using an RGB video signal rather than using composite video is well worth the sacrifice of a completed deterring process as you know there are various types of analog video signals transported via various types of connectors component s-video composite and RF via coax or a few of the cables used to transport video from an output device to a display device they exist so video can be broadcast or stored using less bandwidth than RGB originally we only needed a brightness signal for TV when color TV arrived color was mixed into that signal to maintain backward compatibility for black and white TV sets the various analog video standards descended from this simple two-step approach number one take a black-and-white signal and number two now what the heck are we gonna do about color the human eye can perceive brightness details much more than it can color details so it makes sense to focus on reducing color information in order to save bandwidth color bandwidth and therefore color resolution is compromised the further you travel down the quality ranking for analog video when you reach the point of combining the brightness and color information into one signal you will experience a notable reduction in color versus the original RGB signal and notice instances of visual artifacts in the picture both computers and consoles have embraced and Exploited these two results of bandwidth reduction and this is key when it comes to making an argument for composite video let's take a look at how color is included in the various video standards component video and s-video provides separated brightness and color information of the original RGB signal these signals are referred to as luma and chroma a display can take these separate components and use them to derive a fairly decent representation of the original RGB signal composite in RF however contain a combined luma and chroma signal the display then has to separate the brightness and color information before proceeding to reproduce an RGB signal [Music] the separation process or filtering of the chroma from the luma can vary in quality depending on the types of filters used the typical filter used for this process is called a comb filter and there are various types some sort of filtering method is needed to separate luma and chroma where composite video and RF are used and the superior comb filtering your CRT cost you more money sometimes the separation process incorrectly interprets luma information as chroma information and vice-versa resulting in visual artifacts in the image take the color bleed check screen from the 240p test suite for example the bottom set of lines alternate between black and white when viewed using composite video there is color there where we know there should not be this is because brightness information is being interpreted as color information on the flip side color interpreted as brightness we sometimes see dot crawl such as the odd appearance of bright squares and the orange letters on this screen the graphical output of the Sega Genesis used dithering combined with the degraded fidelity of composite video to help simulate transparency and additional colors the most often cited example of this is a waterfall in Sonic the Hedgehog so let's see how it's done I'll start with an emulator to walk you through the various graphics involved in the dithering process let's disable the sprites used so we can focus on the waterfall the background is made up of two layers the Far background that is behind the waterfall and the near background that contains the waterfall itself and the surrounding terrain the waterfall is made up of four shades of blue in single pixel with columns that have a 1 pixel width gap between each column the movement of the waterfall that you see is actually a static image undergoing a pilot cycle a pallet cycle is the process of taking a defined number of pallet positions for in this case and cycling the values of each of the four in the same order it creates an illusion of animation without taxing the processor in addition to the near background the far background also uses the technique for a waterfall and shimmering on the water surface layering the two backgrounds creates a Dillard pattern with a plethora of colored detail when this is converted from RGB to composite and back again the fine detail of the colors is lost and they appear blended together producing what to us is simply a semi-transparent waterfall here is a real-life example the same waterfall running on a Sega CD X hooked up to a sony PVM via RGB the alternating lines of waterfall and those of the far background are just as jarring as they were in the emulator now here is the same scene using the same console and display but connected via composite video notice the compromise details result in a semi-transparent waterfall a creation of extra colors that aren't in the genesis palette and a bit of a rainbow effect here's the same scene in composite video on a 2005 TV the water blending is there and the rainbow effect is also there here is a capture of the system using the framemeister upscaler same story and as an added of shock value here's a model one Genesis with bad combining of the chroma and luma signals same 2005 TV set and therefore same comb filter circuit but improper creation of the composite video signal I assume this is an example of a terrible amount of luma information being present in the chroma signal let's take a look at a slightly more active example shinobi 3 this particular area makes use of dithering in a couple of places the pool area and the waterfalls both instances allow sprite information to appear and pass behind them for added effect this footage is from the 2005 TV whereas the sonic scene I used to require a bit of time to stop and smell the roses to see composite video artifacting in effect shinobi 3 puts it right in your face if we examine the same scene in an emulator you can see the checkerboard dithering in the pool area and vertical lines for the waterfalls just like in Sonic as a side note there are actually two sets of pallet cycles going on here one for the far background and one for the near background with the double palette cycle and dithering in place I think the graphics make for a great atmosphere now let's focus a bit more on extra color creation the title screen of Sonic 2 uses a checkerboard pattern combining five different shades of blue and white horizon to produce a gradient the checkerboard pattern is easily observed in the emulator and creates extra colors with composite video effectively producing a smoother gradient one wonderful example of dithering for the purposes of color and shading is this level loading screen from earthworm jim an emulator naturally shows the raw makeup of this screen quite well and you can observe instances of checkerboard patterns and the eyes and face as well as the alternating vertical line technique especially along parts of his uniform at the back also note the tip of his gun a red glow is made using a combination of bright red very dark red alternating vertical lines close to the tip of the gun and dot work further away from the tip the same details can be observed in the RGB signal on a PV M there were a few anomalies from capturing it with my camera but the separation of lines and dots can still be seen now the same capture using composite video on the PBM notice how the intricate checkerboard and line work has blended in on his face in his eyes the backpack has more of a gradient look to it and the tip of the gun looks like it is glowing instead of a smattering of pixels here's the same image using the 2005 TV the anomalies are not as pronounced as my footage of the PBM you can see the smooth gradient in the uniform at the back obviously anything from a CRT is going to look better in person but I think this composite video based image is a much more organic representation of earthworm jim than the checkered and barred version the dithering continues in the level itself in composite mode you can see the blending of the shadows of the ground in various bits of shading on the tires to add depth to the scene returning to RGB the dots on the ground as well as the vertical bar makeup to the dithering of the tires can now be seen dithering is used in many games for the platform whether or not you wish to abandon RGB for composite video in order to experience it is up to you I hope you enjoyed this examination of dithering for the Sega Genesis if you would like to see more videos like this one please like the video and subscribe to the channel leave a comment as to whether you have an appreciation for what games did with composite video or if RGB is a reason to leave it all behind if you would like to become a patron I have provided a link to patreon in the video description thank you very much for watching [Music]

Channel: Displaced Gamers

Views: 263,459

Keywords: Dithering, Sega Genesis, Sega Mega Drive, Composite Video, S-Video, RGB, RF, Transparency, Palette Cycle, Sonic the Hedgehog, waterfall, Earthworm Jim, Shinobi 3, CRT, programming, Mega sg

Id: x0weL5XDpPs

Length: 10min 30sec (630 seconds)

Published: Fri Jul 27 2018