If you don't need a color conversion it's even more simple.
You need something like this:
void DrawBitmap(BitmapType *bmp)
{
UInt16 err;
BitmapType *myBmp;
UInt8 *src, *dst;
Int16 i;
myBmp = BmpCreate( bmp->width, bmp->height, 4, NULL, &err );
if ( err != errNone )
return;
src = (UInt8*) BmpGetBits( bmp );
dst = (UInt8*) BmpGetBits( myBmp );
// convert from 8 bit to 4 bit grayscale
for ( i = 0; i < bmp->width * bmp->height / 2; i++ )
{
UInt8 b, bHi, bLo;
b = *src++;
bHi = b >> 4; // 8bit -> 4bit - we ignore 4 low bits
b = *src++;
bLo = b >> 4;
*dst++ = (bHi<<4) | bLo;
}
WinDrawBitmap( myBmp, 0, 0 );
BmpDelete( myBmp );
}
Very simple isn't it? What's the problem?
If the original bitmap has 0 value as black and 255 as white (standard
grayscale format) you need to invert it (just use ~(b>>4) in conversion).
For color original bitmap you should get RGB from the palette for every
pixel and convert to grayscale using formula like I wrote in my previous
letter.
Good luck,
Alex
PS. It's for PalmOS 3.5 of course. For earlier versions you have to write
your own BmpXXXX() functions. But it's not difficult.
----- Original Message -----
From: "Hans Han"
Sent: Monday, November 13, 2000 12:38 PM
Subject: Re: How to convert a 8-bits bitmaps to 4-bits Grayscale bitmaps
> Hi,
>
> For preformance reason, I want write on the Bitmap data area of an
> offscreen window directly while I receive the bitmap from network. The
> pixel size of window is 4 , so how to covert the 8-bits grayscale values
to
> 4-bits index value? Wait for help.
>
> Regrads
>
> Hans
> ----- Original Message -----
> From: "Hans Han"
> Sent: Friday, November 10, 2000 4:12 PM
> Subject: How to convert a 8-bits bitmaps to 4-bits Grayscale bitmaps
>
>
> > Hi All,
> >
> >
> > I wonder how to convert 8-bits bitmaps to 4-bits Grayscale bitmaps.Any
> tips
> > or sourcecode are welcome.
> >
> > Thanks
> >
> > Hans
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