Re: MMX speedup for Floyd Steinberg error diffusion

On May 7, 11:35 pm, "Maarten Kronenburg" <spamt...@xxxxxxxxxx> wrote:
"Maarten Kronenburg"  wrote in message

Now I see the data is in bytes. In that case it seems better to put 16 bytes
in an 128-bit xmm register, then put 8 bytes each time into 8 16-bit words
by shifting and anding, and do the above with PSLLW/PSRLW and PADDW/PSUBW in
the 16-bit words. Then the scaling mentioned is not needed because the upper
8 bits in the 16-bit words should be zero.
Maarten.

Thanks...

The thing is Floyd-Steinberg dithering works serially one pixel at a
time... Each pixel processed affects the pixel to its right and the
pixels on the next scanline.
So the best I can hope for is to handle one pixels R, G and B byte
values in one go.

Let me clarify with actual code ( highly unoptimal C++ , for clarities
sake )

/////////////////////////////////////////////////
struct RGBA {unsigned char r, g, b, a; };

int saturateAdd(int a, int b)
{
int ret = a + b;
if(ret < 0) return 0;
if(ret > 255) return 255;
return ret;
}

void diffuse(RGBA* pImg, int w, int h)
{
for(int y = 0; y < h; ++y)
{
RGBA* pPix = pImg + (y * w);
for(int x = 0; x < w; ++x, ++pPix)
{
RGBA bestMatch = getNearestPalColor(pPix);
int rDiff = pPix->r - bestMatch.r;
int gDiff = pPix->g - bestMatch.g;
int bDiff = pPix->b - bestMatch.b;


RGBA* pNext = pPix + 1;
pNext->r = saturateAdd(pNext->r, (rDiff * 7) >> 16);
pNext->g = saturateAdd(pNext->g, (gDiff * 7) >> 16);
pNext->b = saturateAdd(pNext->b, (bDiff * 7) >> 16);

// repeat 3 lines above for pixel below, below left and
below right with co efficients 5, 3 and 1
}
}
}

///////////////////////////////////////////////

Since logical and multiply arent available for 8 bit operands, heres
what im thinking....

The pixel bytes lets say are RGBA
I do a PUNPCKLBW getting bytes XRXGXBXA in an MMX register
The X are unwanted values.
Then I do a PAND with 0x00FF00FF00FF00FF , getting rid of the X's

I repeat the same process for the new palette pixel

Then I can do a PSUB to get 4 signed differences
Then PMULLW with the coefficient value like 0x0007000700070007
and PSRAW to shift

Now i have 4 signed WORDs in some MMX register which are the signed
differences between the original and palettized pixel colors...

Now how do i add these to the destination pixel with saturated
addition?

There are instructions for adding signed values with signed saturation
and unsigned values with unsigned saturation.
How do i add signed differences to unsigned values with unsigned
saturation?

Perhaps some sort of tricky bit manipulation can work?

Anyhow even if i get this far and have to do the rest normally without
MMX, it should be much simpler code than the horror that my compiler
generates for the above C++ code.

Further ideas appreciated...

Vivek

.

Relevant Pages

  • Re: MMX speedup for Floyd Steinberg error diffusion
    ... Each pixel processed affects the pixel to its right and the ... int saturateAdd ... This is a signed addition with unsigned saturation. ... Note that for unsaturated add and subtract, ...
    (comp.lang.asm.x86)
  • Re: dilation
    ... one pixel off, and I had array index out of bound errors). ... int foreground = 255; ... //create binary image from the input image ... //foreground, i set it to foreground value and exit for cycle. ...
    (sci.image.processing)
  • Malloc code
    ... set up some data in a strucuture called GMM. ... struct GMM{ ... will be displayed starting at pixel. ... int SETWINEXTHORZ_MSB, ...
    (microsoft.public.vc.language)
  • Re: Back to getting pixel RGBColor values from a pixmap
    ... >> RGBColor getpixel(GWorldPtr Source, int H, int V) ... > you can have a 16x16 pixel GWorld with topleft at. ...
    (comp.sys.mac.programmer.help)
  • Re: Problems with BufferedImage and ColorModel
    ... > I've been experimenting with BufferedImage and am attempting to extract the ... > individual R, G, B, and Alpha values from the color of each pixel in an image. ... > I pass that value to the getRedmethod of the ColorModel I get from ... is coded into the int value returned from getRGB. ...
    (comp.lang.java.help)