Success: Xenarc, Epia MII, and aspect ratio under Linux

**millec** · 05-25-2004, 12:22 AM

Many of us are trying to find a way to get the native screen resolution of our Xenarc monitors (800x480). This screen resolution has an aspect ration of 1.67. It turns out that 1280x768 also has this aspect ratio and looks very good on the Xenarc. I am using Linux, but Windows users may be able to find this screen resolution with their driver as well (I haven't looked).

I am running Gentoo Linux using the viafb framebuffer driver. I have added options to my grub bootloader telling it to load the viafb driver and set the screen resolution to 1280x768 @60Hz. This works perfectly.

--Craig

**NoPistonPC** · 05-25-2004, 12:52 AM

I think that a lot of people are tryin to get the 800x480 resolution to work because at this resolution there is a one-to-one mapping between screen coordinates and LCD pixels. Therefore, no scaling or aliasing aritifacts will appear on your screen. A good way to check is to set your X-windows background to the default black and white checkerboard pattern. If there is not a one-to-one pixel mapping, you will see moire patterns (wavy looking lines) on the background. Of course, in linux, using X-windows, you can get any graphics card to display 800x480 by typing in the right modeline.

**millec** · 05-25-2004, 01:01 AM

Originally Posted by NoPistonPC

I think that a lot of people are tryin to get the 800x480 resolution to work because at this resolution there is a one-to-one mapping between screen coordinates and LCD pixels. Therefore, no scaling or aliasing aritifacts will appear on your screen. A good way to check is to set your X-windows background to the default black and white checkerboard pattern. If there is not a one-to-one pixel mapping, you will see moire patterns (wavy looking lines) on the background. Of course, in linux, using X-windows, you can get any graphics card to display 800x480 by typing in the right modeline.

Exactly. This screen resolution has the exact same aspect ratio, therefore no distortion. A higher resolution with the same aspect ratio accomplishes the same thing. There are no scaling or aliasing artifacts with this screen resolution.

--Craig

**NoPistonPC** · 05-25-2004, 01:17 AM

Just consider the vertical dimension. How can you fit 768 vertical pixels into 480 physical elements on the LCD display without scaling artifiacts (i.e. without losing information)? It's like trying to display 3 pixels of information in 2 pixels. For instance, in the 1280x768 mode, if you have a letter that's 2-pixels high (bear with me), then try to map it into 480 physical pixels, part of that letter will get lost. Granted, if you all you are doing is watching DVD movies, it will be fine since you are just scaling the video up to the high resolution, then scaling it back down again. But, if you are trying to read small text, it will get distorded. For the purposes of a CarPC, you will probably be fine.

**millec** · 05-25-2004, 01:37 AM

Originally Posted by NoPistonPC

Just consider the vertical dimension. How can you fit 768 vertical pixels into 480 physical elements on the LCD display without scaling artifiacts (i.e. without losing information)? It's like trying to display 3 pixels of information in 2 pixels. For instance, in the 1280x768 mode, if you have a letter that's 2-pixels high (bear with me), then try to map it into 480 physical pixels, part of that letter will get lost. Granted, if you all you are doing is watching DVD movies, it will be fine since you are just scaling the video up to the high resolution, then scaling it back down again. But, if you are trying to read small text, it will get distorded. For the purposes of a CarPC, you will probably be fine.

OK... If this can look even better, then I would love to learn how. :-) So far, google has not yielded anything. Does anyone know how to put the framebuffer into the native resolution of the xenarc?

--Craig

**millec** · 05-25-2004, 01:44 AM

Also... even if there are artifacts due to screen resolution, at least everything is being sent in a resolution that has the same proportions. This makes everything including text, look much much better than say, 800x600 or one of the other non-native resolutions that havea different aspect ratio than the native resolution.

--Craig

**NoPistonPC** · 05-25-2004, 02:02 AM

Originally Posted by millec

Also... even if there are artifacts due to screen resolution, at least everything is being sent in a resolution that has the same proportions. This makes everything including text, look much much better than say, 800x600 or one of the other non-native resolutions that havea different aspect ratio than the native resolution.

That's true. I agree with you here.

I have the Xenarc 700TSV (the new model) and I used this modeline in my XF86Config file to get 800x480@60Hz:

Code:

Modeline "800x480" 31.746 800 860 940 1000  480 508 511 525 -hsync -vsync

I think the framebuffer device uses a similar modeline format so try it out.

In windows, if you have a graphics card that supports custom resolutions, get PowerStrip and set it up like this:

**millec** · 05-25-2004, 02:47 AM

Right on! Thanks for the XF86 modeline.

--Craig

**NoPistonPC** · 05-25-2004, 03:00 AM

No problem. Let me know if it works for you...

**millec** · 05-29-2004, 01:23 AM

I cannot get this resolution to work with the Epia chipset. NoPistonPC, did you get this working under X with the Epia chipset, or with your Radeon (as shown in powerstrip)?

Thanks,
--Craig

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