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What do I need for 30bpp?
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Ant P.
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PostPosted: Sat Nov 17, 2012 7:17 pm    Post subject: What do I need for 30bpp? Reply with quote

Hi.

I've got a screen that can do 30bpp modes (Dell U2410), a graphics card that should support it (R700 Radeon) and a choice between DVI or HDMI. I'm currently using the DVI connection and starting X with -depth 30 gives an error that the Radeon driver doesn't support 30bpp. Should I give up now, or do I just need a different cable?
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NeddySeagoon
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PostPosted: Sat Nov 17, 2012 8:03 pm    Post subject: Reply with quote

Ant P.

30 is a very strange number for colour depth. Its usually 1,8,15,16,24 and 32.

The U2410 specification does say Colour Support: 1.07 billion colours, which is 30 bits.
You need a lot more than just a video driver to do 30 bit colour. Xorg and your applications need to support it too.

Xorg actually uses 32 bit colour internally. Thats 8 bits each for RGB and Alpha, which is the transparency.
This fits in quite nicely with the way CPUs work, in bytes, words and double words. 8, 16 and 32 bits.
The numbers in my opening sentence are not random - fit with CPU internal operations.

HDMI and DVI both support 30 bpp. In fact, definitions for 36 and 48 bpp are in place.
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chithanh
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PostPosted: Sat Nov 17, 2012 8:06 pm    Post subject: Reply with quote

To my knowledge, the U2410 supports 30-bit color only through the DisplayPort input. But I could be wrong there.

To what extent the radeon driver supports 30-bit I don't know, you will have to ask the upstream developers (#radeon on irc.freenode.net or their mailing list xorg-driver-ati@lists.x.org).
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Ant P.
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PostPosted: Sat Nov 17, 2012 10:49 pm    Post subject: Reply with quote

chithanh wrote:
To my knowledge, the U2410 supports 30-bit color only through the DisplayPort input. But I could be wrong there.

This seems to be the case, from what I've been reading. I've got an AMD E450 attached via DP, but I don't use that as a desktop and my main PC only has the other two.

I'll forget about it for now, I only started looking because someone in another thread was having problems with 30bpp on nvidia-drivers... wanted to see if I could reproduce the bug :)
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