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2005.10.27 13:57 "Re: How located pixels with BitsPerSample not bound to byte?", by Frank Warmerdam
On 10/27/05, ϋΕΒΕΛΟ εΧΗΕΞΙΚ wrote:
> If we talking about testing exotic images.
>
> Look at the flower-rgb-contig-12.tif from the test images.
> It have RGB,Uncompressed, PlanarConfig=Continue, and
> BitsPerSample=12
>
> How the pixels are located inside a strip in such case?
> I really cann't understand :)
>
> Is it correct?
>
> Bytes: 0 | 1 | 2 | 3 | 4
> Bits : 76543210|7654|3210|76543210|76543210|7654|3210
> Pixels: rrrrrrrr|rrrr|gggg|gggggggg|bbbbbbbb|bbbb|rrrr|
> Samples: hiR |lowR|hiG | lowG | hiB |lowB| hiR
Eugene,
I thought it should work as you have shown, but when
I review my code it seems the first byte will be the low
order 8bits of red, not the high (and so forth). I am including
my code for arbitrary unpacking of odd bit data into words
though it may be a bit opaque. I believe Bob uses a more
efficient solution.
/* -------------------------------------------------------------------- */
/* Handle 1-32 bit integer data. */
/* -------------------------------------------------------------------- */
else
{
int iBit, iPixel, iBitOffset = 0;
int iPixelBitSkip, iBandBitOffset, iX, iY, nBitsPerLine;
if( poGDS->nPlanarConfig == PLANARCONFIG_CONTIG )
{
iPixelBitSkip = poGDS->nBands * poGDS->nBitsPerSample;
iBandBitOffset = (nBand-1) * poGDS->nBitsPerSample;
}
else
{
iPixelBitSkip = poGDS->nBitsPerSample;
iBandBitOffset = 0;
}
// bits per line rounds up to next byte boundary.
nBitsPerLine = nBlockXSize * poGDS->nBitsPerSample;
if( (nBitsPerLine & 7) != 0 )
nBitsPerLine = (nBitsPerLine + 7) & (~7);
iPixel = 0;
for( iY = 0; iY < nBlockYSize; iY++ )
{
iBitOffset = iBandBitOffset + iY * nBitsPerLine;
for( iX = 0; iX < nBlockXSize; iX++ )
{
int nOutWord = 0;
for( iBit = 0; iBit < poGDS->nBitsPerSample; iBit++ )
{
if( poGDS->pabyBlockBuf[iBitOffset>>3]
& (0x80 >>(iBitOffset & 7)) )
nOutWord |= (1 << (poGDS->nBitsPerSample - 1 - iBit));
iBitOffset++;
}
if( eDataType == GDT_Byte )
((GByte *) pImage)[iPixel++] = nOutWord;
else if( eDataType == GDT_UInt16 )
((GUInt16 *) pImage)[iPixel++] = nOutWord;
else if( eDataType == GDT_UInt32 )
((GUInt32 *) pImage)[iPixel++] = nOutWord;
}
}
}
Best regards,
--
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I set the clouds in motion - turn up | Frank Warmerdam, warmerdam@pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush | Geospatial Programmer for Rent