Re: vImage
Re: vImage
- Subject: Re: vImage
- From: Shawn Erickson <email@hidden>
- Date: Fri, 9 Jan 2004 16:42:33 -0800
On Jan 9, 2004, at 4:01 PM, Amedeo Paglione wrote:
Hi all,
I'm trying to use the vImage library to resize an image but I always
get an exception executing the vImageScale_ARGB8888 function.
Here is an extract from the simple test code:
NSBitmapImageRep * theImage = [ NSBitmapImageRep
imageRepWithContentsOfFile:filename ];
if( theImage != nil )
{
src = (vImage_Buffer*)malloc(sizeof(vImage_Buffer));
bpp = [ theImage bitsPerPixel]/8;
MyInitBuffer(src, [theImage pixelsHigh], [theImage pixelsWide], bpp);
bytesPRow = [theImage bytesPerRow];
h = [theImage pixelsHigh];
memcpy(src->data, [theImage bitmapData], h * bytesPRow);
dest = (vImage_Buffer*)malloc(sizeof(vImage_Buffer));
MyInitBuffer(dest, 300, 300, bpp );
vImageScale_ARGB8888(src, dest, NULL, 0); // Here it is the ERROR
MyFreeBuffer(dest);
MyFreeBuffer(src);
}
Why the copy? You should just be able to get the pointer to image data
and wrap that data with a vImage_Buffer.
Anyway I believe you need to specify something for the flags field,
zero is not a valid option for this operation. The docs list the
following...
kvImageBackgroundColorFill
If set, the function will use the Background Color Fill technique to
access pixels outside the source image.
kvImageEdgeExtend
If set, the function will use the Edge Extend technique to access
pixels outside the source image.
kvImageDoNotTile
If set, the function will not do internal tiling. This is appropriate
if you do tiling yourself.
kvImageHighQualityResampling
If set, the function will use a Lanczos5 kernel for resampling.
Otherwise it will use a Lanczos3 kernel.
The kvImageBackgroundColorFill and kvImageEdgeExtend flags are mutually
exclusive. You must set exactly one of these flags. See Pixels Outside
the Image Buffer.
I cannot locate the message now but I believe an Apple employee just
emailed a code snippet that outlined how to resize an image in Cocoa
without resolution loss.
-Shawn
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| References: | |
| | >vImage (From: Amedeo Paglione <email@hidden>) |