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Thread: FAQ: VGA vs. Composite (Video) Screens

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    FLAC cproaudio's Avatar
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    VGA vs Composite

    I've read many posts regarding VGA screens vs Composit LCD screens. I thought I make an educational post about it

    LCD is LCD no matter if its low resolution or high resolution or STN aka dual scan or TFT aka active matrix. There are STN VGA, STN composit, TFT VGA and TFT composit LCD screens. Price varies from super low cost STN composit to low cost TFT composit screens to mid cost STN VGA screens to high cost TFT VGA screens. Gains screen (Xenarc, DScustoms, DigitalWW) and Lilliput VGAs are all TFT VGA screens. STN screens dont refresh fast enough to be used for video viewing and often not bright enough. Avoid STN screens at all cost.

    I will be focussing on TFT screens.

    A true VGA screen will have an LCD screen that's true VGA resolution of at least 640X480 and a controller that has a VGA input and can handle VGA resolutions. Newer generation 7" wide VGA screens have an LCD panel capable of displaying 800X480 native resolution. The controller will compress any resolution up to 1600X1200 down to 800X480. This means when you set your computer to display 800X600 or 1024X768, the LCD controller scales that down to 800X480.

    Composit screens can be broken down to 2 categories, high resolution LCDs and low resolution LCDs. either ones will use an LCD controller that has RCA and or S-video inputs.

    High resolution composit screens have LCD screens that's capable of VGA resolution but the controller has only RCA input. DigitalWW's TM-701L is one such screen. You can purchase VGA controller for it and turn it into a true VGA screen. Alpine's IVA-D900 indash DVD player/monitor has a Wide VGA screen but only accepts RCA input. I havent read any VGA mods for it yet. PSone LCD screens will probably fall under this category though it is questionable. I cant find any resolution specs for it. The screen takes RGB input. People have sucessfully modified the PSone LCD screen to accept VGA input. I got a chance to see one in person. The picture looks very sharp but it looked like it had some horizontal lines on the screen.

    Low resolution composit screens uses LCD panels like 1152X234 or 960X234 with controllers that have only RCA input. Majority of the composit screens fall under this category.

    Resolution spec can be misleading. A single pixel has 3 sub pixels representing 3 colors (red, green, blue). Most manufactures count the sub pixels as being 1 pixel. That's why you see composit screens with 1152X234 or 960X234 resolutions. If that's the case, a 7" wide VGA screen would have 2400X480 which makes it a mega-pixel LCD screen.

    protential problem when using composit screen. First of all the ovious, it's blurry. RCA video jack can only handle 240 lines of resolution. So you are bacially compressing 480(VGA), 600(SVGA), 768(XGA) down to 240 lines of res. not to mention it's interlaced. Second protential problem is flickers. Every PC to TV converter and video cards TV out that I've seen have flicker problems. No matter what flicker setting you use, you will always have flickers. I think it's due to NTSC standards.

    This is a close up picture of a 7" Xenarc VGA (1st gen) running 848X480 resolution. This screen will not run any higher res than # # # X 480. 2nd generation Gains screen will display up to 1920X1200. It is pointless to run at such high resolution cuz you cant see the details. You can compare the time/date/clock and the green VNC icon to the rest of the pic.


    This is a close up picture of a 6.4" composit LCD. It's an Accel LCD64A native resolution is 960X234. Resolution is set at 640X480 for maximum clarity. I used a TView Gold PC to TV converter to convert VGA to Composit. The LCD screen only accepts RCA input. The time and date is so blurry that you cant see them. The green VNC icon is next to the red VNC icon. It's so blurry that you cant tell what it is.


    I dont have a high resolution composit LCD laying around so I couldnt take a close up screen shot. I did however manage to simulate it. I connected the TView Gold's RCA output to my home PC's ATI AIW's video input and capture the screen. This pic basically shows the limitations of RCA jacks and shows how the display might look like on a high resolution composit screen. It looks pretty close to the real thing as I recall seeing similar setup. You can see the time/date and the green VNC but somewhat blurry. This is OK as long as you dont run GPS apps unless you can change the font size.


    If I missed something PM me and I'll correct it. Also this is not a disgussion thread so please dont post here unless you can contribute to this FAQ.
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    Jesus Freak antimatter's Avatar
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    The screens that come with your car or your head unit or your GPS are video, not VGA screens and are much lower resolution than VGA. This post has pictures of what a computer output looks like on a video screen. This uses an additional piece of hardware called a scan converter to clean up the picture as much as possible.

    Take a look at the desktop below. Note how little space there is between the Start menu and the taskbar icons on the right. There is only enough room to display two running applications. Note also how few icons are on the desktop and the fuzziness around the text. The reason for this is that the display settings have been cranked way down to something on the order of 640 X 480 or less.

    This is necessary because the video standard is nowhere near as crisp and clean as a VGA screen. That means two things - you display less and what gets displayed doesn't look clean. With exactly the right skin and colors, you can make it work, but just recognize that it is a compromise.


    In addition, you can see that the desktop is cut off slightly at the top. It is theoretically possible to fix this but the video standard works in such a way that it is intended to cut off a bit all the way around because early TV sets had a bezel around the tube.


    Note in this image how much screen real estate the Google page takes up. Almost the entire vertical and horizontal space. Note also that the text appears fuzzy. As a comparison, load Google on your VGA computer screen and shrink the window down until it is roughly the same appearance of this image. That's how much space you'll get on your car PC desktop if you use a video screen.



    Bottom line - if you have a very specific type of installation such as just using Road Runner as a music player and perhaps video player, then a video screen might work for you. You can control the size and color of the text with a special or simplified skin that reduces the blurriness and deals with the color problems and handles the cutoff around the sides. Navigation is possible, but you want to be able to tweak the font sizes, colors, etc.

    However, if you want a full up PC with web browsing, intend to use the desktop, and so forth, the limitations of the video screen will be revealed to those who check out your installation. It will make it look cheap because of the fuzziness of the text, the washed out colors, and the tiny desktop size. That may be okay with you and if you already have an OEM screen in your car it may be worth it. But if you are just trying to save money on your installation by going with the less expensive video screen, realize that it will be obvious that you took that path.
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