To make blur effect on UIImage iphone Problem? - iphone

Question

Hi here in this code i make the image to blur. but the problem is, it is very slow on iPhone.
here is my code.
- (UIImage*) gaussianBlur:(NSUInteger)radius
{
// Pre-calculated kernel
double dKernel[5][5]={
{1.0f/273.0f, 4.0f/273.0f, 7.0f/273.0f, 4.0f/273.0f, 1.0f/273.0f},
{4.0f/273.0f, 16.0f/273.0f, 26.0f/273.0f, 16.0f/273.0f, 4.0f/273.0f},
{7.0f/273.0f, 26.0f/273.0f, 41.0f/273.0f, 26.0f/273.0f, 7.0f/273.0f},
{4.0f/273.0f, 16.0f/273.0f, 26.0f/273.0f, 16.0f/273.0f, 4.0f/273.0f},
{1.0f/273.0f, 4.0f/273.0f, 7.0f/273.0f, 4.0f/273.0f, 1.0f/273.0f}};
NSMutableArray *kernel = [[[NSMutableArray alloc] initWithCapacity:5] autorelease];
for (int i = 0; i < 5; i++) {
NSMutableArray *row = [[[NSMutableArray alloc] initWithCapacity:5] autorelease];
for (int j = 0; j < 5; j++) {
[row addObject:[NSNumber numberWithDouble:dKernel[i][j]]];
}
[kernel addObject:row];
}
return [self applyConvolve:kernel];
}
- (UIImage*) applyConvolve:(NSArray*)kernel
{
CGImageRef inImage = self.CGImage;
CFDataRef m_DataRef = CGDataProviderCopyData(CGImageGetDataProvider(inImage));
CFDataRef m_OutDataRef = CGDataProviderCopyData(CGImageGetDataProvider(inImage));
UInt8 * m_PixelBuf = (UInt8 *) CFDataGetBytePtr(m_DataRef);
UInt8 * m_OutPixelBuf = (UInt8 *) CFDataGetBytePtr(m_OutDataRef);
int h = CGImageGetHeight(inImage);
int w = CGImageGetWidth(inImage);
int kh = [kernel count] / 2;
int kw = [[kernel objectAtIndex:0] count] / 2;
int i = 0, j = 0, n = 0, m = 0;
for (i = 0; i < h; i++) {
for (j = 0; j < w; j++) {
int outIndex = (i*w*4) + (j*4);
double r = 0, g = 0, b = 0;
for (n = -kh; n <= kh; n++) {
for (m = -kw; m <= kw; m++) {
if (i + n >= 0 && i + n < h) {
if (j + m >= 0 && j + m < w) {
double f = [[[kernel objectAtIndex:(n + kh)] objectAtIndex:(m + kw)] doubleValue];
if (f == 0) {continue;}
int inIndex = ((i+n)*w*4) + ((j+m)*4);
r += m_PixelBuf[inIndex] * f;
g += m_PixelBuf[inIndex + 1] * f;
b += m_PixelBuf[inIndex + 2] * f;
}
}
}
}
m_OutPixelBuf[outIndex] = SAFECOLOR((int)r);
m_OutPixelBuf[outIndex + 1] = SAFECOLOR((int)g);
m_OutPixelBuf[outIndex + 2] = SAFECOLOR((int)b);
m_OutPixelBuf[outIndex + 3] = 255;
}
}
CGContextRef ctx = CGBitmapContextCreate(m_OutPixelBuf,
CGImageGetWidth(inImage),
CGImageGetHeight(inImage),
CGImageGetBitsPerComponent(inImage),
CGImageGetBytesPerRow(inImage),
CGImageGetColorSpace(inImage),
CGImageGetBitmapInfo(inImage)
);
CGImageRef imageRef = CGBitmapContextCreateImage(ctx);
CGContextRelease(ctx);
UIImage *finalImage = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);
CFRelease(m_DataRef);
CFRelease(m_OutDataRef);
return finalImage;
}

Answer 1

A 2-d Gaussian convolution is separable, which means it can be done as 2 1-d convolutions, one horizontal and one vertical. That should save you a bit of time.
http://en.wikipedia.org/wiki/Gaussian_blur#Implementation