Re: Re: [Question] Colour management

["Antonino A. Daplas" <adaplas@hotpop.com>]

On Sunday 01 August 2004 06:19, Alexander Kern wrote:
> Am Samstag, 31. Juli 2004 23:19 schrieb Antonino A. Daplas:
> > On Saturday 31 July 2004 21:31, Ville Syrjälä wrote:
> > > > red_reg[index * 8] = red
> > > > green_reg[index * 8] = green
> > > > blue_reg[index * 8] = blue
> > > >
> > > > Some hardware require that all 8 entries needs to be filled up.
> > >
> > > I noticed you do this in i810fb. What happens if you don't do this?
> >
> >  
> > Wrong colors.
> >
> > > AFAIK mach64 doesn't need this.
> >
> > Yes, it's hardware dependent. When I decided to add directcolor support,
> > I initially copied the mach64's setcolreg function but I got wrong
> > colors at bpp16.  Found out by experimentation that I need to set all
> > 256 entries of the CLUT.
> >
> > Tony
>
> Very scurry, even mach64 give wrong colors for me ;-))
>
> Here are the pics, that demonstrate my errors.

Actually, this is one of the nuances that affect DirectColor at < 24 bpp.
Since RGB565 has only at the most 64 entries (based on the depth of
the green channel), a 224-color logo will be drawn incorrectly. 16-bit
Directcolor actually needs a 16-color logo. Unfortuanately, the logo
drawing code will choose a 224-color logo for Directcolor 16-bit.  This is
problem that I pointed out to James a long time ago when he rewrote the 
logo drawing code. 

It's a little bit surprising that 8-bit pseudocolor can actually draw a
224-color logo correctly, while 16-bit directcolor cannot :-)

Workaround:
	Force fbdev to use 16-color linux logo in the "Boot Logo" option
	of your kernel config.

I'll see if I can find a way for a more definitive fix.

Tony

P.S. This problem might be unique to the logo drawing code.




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