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2010.12.06 23:40 "Re: 16 bit gray scale conversion", by Chris Cox
Different results in what application?
How exactly are they showing differently?
Are they confusing gamma encodings (normally applied to 16 bit/channel ints,
but not to 32 bit/channel floats)?
Yes, normally the linear scaling you are doing should be just fine -- as
long as gamma encoding has been resolve beforehand.
Chris
On 12/6/10 3:27 PM, "Jamie L. Finch" <wi6f@cruzio.com> wrote:
> Dear Tiff Group,
>
> I was assigned a bug in LightWaves bump mapping.
> The complaint was that 16 bit tiffs do not show the same results as 32
> bit tiffs.
> I wanted to make sure that I am converting the tiffs to floating point
> correctly.
> I am most interested in 16 bit PHOTOMETRIC_MINISBLACK, which is the else
> case. Can anyone confirm that the conversion from short to float is
> correct ?
> This conversion is before any color correction is applied.
>
> Jamie Finch
> NewTek, Inc.
>
>
> /* Extract pixel values and send to LW... */
>
> for( i = 0; i < Height; i++ ) {
> TIFFReadScanline( tif, InBuf, i, 0 );
> Sorc.SS = (short *) InBuf;
> Dest.FP = (float *) IndexLine;
> switch( BitsPerSample ) {
>
> /* Grayscale. */
>
> case 16:
> if( Photometric == PHOTOMETRIC_MINISWHITE )
> { /* Gotta reverse values. */
> for( j = 0; j < Width; j++ )
> *Dest.FP++ = ( 65535.0F - (float)
> *Sorc.US++ ) / 65535.0F;
> }
> else {
> for( j = 0; j < Width; j++ )
> *Dest.FP++ = ( (float) *Sorc.US++ )
> / 65535.0F;
> }
> break;
>
> /* Grayscale. */
>
> case 32:
> if( Photometric == PHOTOMETRIC_MINISWHITE )
> { /* Gotta reverse values. */
> for( j = 0; j < Width; j++ )
> *Dest.FP++ = 1.0F - *Sorc.FP++;
> }
> else {
> for( j = 0; j < Width; j++ )
> *Dest.FP++ = *Sorc.FP++;
> }
> break;
> }
> if( LWIP_SENDLINE( ip, i, IndexLine ) != 0 )
> break;
> }
>
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