ubb-vga version 2, more image sources and better color mapping
jon at rejon.org
jon at rejon.org
Thu Apr 28 10:54:38 EDT 2011
This is totally cool. Great if we can run flickernoise on the nanonote
and some other audio applications, then we have a small performance
On Thu, Apr 28, 2011 at 9:37 AM, Werner Almesberger
<werner at almesberger.net> wrote:
> David Kuehling wrote:
>> Werner, you're a genious. Zooming into the image, I can't see see any
>> dithering. How did you manage that many colors?
> Here's the circuit:
> Each color channel gets a signal level that has about 2/3 from the
> respective binary color channel plus a shared binary luminance value
> that contributes 1/3 of the level.
> The board isn't very difficult to make. If you look at
> R5-R7 are soldered SMT-style to the UBB contacts. I placed R8-R10
> directly underneat the board, soldered in the same way. (They just
> need a bit more heat, because they're soldered to the ground plane.)
> R3 crosses from "blue" all the way to Y. I then soldered R1 and R2
> to the long leg of R3. Last but not least, R4 is soldered SMT-style
> To minimize mechanical strain during assembly, I combined the three
> resistor triplets by twisting their VGA-side wires together. Then I
> soldered them to UBB and finally added solder on the VGA side, too.
> I did this last so that I would still have some wiggle room when
> working on the UBB side.
>> You might want to have a look at the color lookup code used in the
>> allegro game library (alleg.sf.net). They used a 2^5 x 2^5 x 2^5 lookup
>> table for RGB -> palette color mapping,
> Ah, very good. Yes, that sounds useful. Right now, I iterate
> through all 16 possible values and compute the (squared) distance
> within the RGB cube. It doesn't really take all that much time,
> but it can't hurt to make this more efficient.
>> Plus you already have code for loading files into bitmaps (bmp, tga or
> Oh, implementing the few simple things I need for my tests probably
> takes less time than even matching APIs and sorting out library
> dependencies would :-) Besides, I had the PPM loader already.
> - Werner
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