Greg Koelpien ha escrito:
> To make a long story short, on my Mac I can have thousands of colors if
> I use a 60Hz refresh rate, but only 256 colors if I use a 72Hz refresh
> rate. Why is this, and can I make any modifications that would allow me
> to use both thousands of colors at the higher refresh rate?
The problem is the VRAM's memory bandwidth (the speed at which the video
memory can transfer data). You need to transfer the entire video memory
contents for each frame, so the needed bandwidth for a given video mode can
be calculated like this:
Screen width * Screen Height * Bits per pixel * Refresh rate / 8
This formula gives the bandwidth in bytes per second - to obtain the
bandwidth in megabytes per second, just divide by 2^20. Oh, and by the way,
don't confuse video memory bandwidth, measured in bytes/s or Mb/s, with the
video signal badwidth, measured in Mhz ;-) .
As you see, video memory bandwidth is proportional to both the bits per
pixel and the refresh rate. Taking into account that a thousands color
display uses double the bits per pixel than a 256 color one (16 versus 8),
and thus it doubles the bandwidth at the same refresh rate, it explains why
you can't get the thousands color mode at 72 Hz: you are reaching the
hardware's limit and need to lower the refresh rate if you want more colors.
Try to apply the above rule to different pixel depths and refresh rates and
compare the values. Pixel depths for different video modes are the
following:
Depth Mode
1 Monochrome
2 4 grays
4 16 grays/16 colors
8 256 grays/256 colors
16 Thousands colors (hi color)
24 Million colors (true color)
Greetings,
Antonio Rodr�guez (Grijan)
<ftp://grijan.cjb.net:21000/>
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