Convert an image into polaroid filter - objective-c

Question

I am trying to convert an image into polaroid filter in the following way:
int m_width = self.size.width;
int m_height = self.size.height;
uint32_t *rgbImage = (uint32_t *) malloc(m_width * m_height * sizeof(uint32_t));
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(
rgbImage,
m_width,
m_height,
8,
m_width * 4,
colorSpace,
kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipLast
);
CGContextSetInterpolationQuality(context, kCGInterpolationHigh);
CGContextSetShouldAntialias(context, NO);
CGContextDrawImage(context, CGRectMake(0, 0, m_width, m_height), [self CGImage]);
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
// now convert to grayscale
uint8_t *m_imageData = (uint8_t *) malloc(m_width * m_height);
for(int y = 0; y < m_height; y++)
{
for(int x = 0; x < m_width; x++)
{
uint32_t rgbPixel=rgbImage[y*m_width+x];
uint32_t redIn = 0, greenIn = 0,blueIn = 0,max = 0,min = 0,chroma = 0,hue = 0,saturation = 0,redOut = 0,greenOut = 0,blueOut = 0;
redIn = (rgbPixel>>24)&255;
greenIn = (rgbPixel>>16)&255;
blueIn = (rgbPixel>>8)&255;
//NSLog(#"redIn %u greenIn %u blueIn %u",redIn,greenIn,blueIn);
max = redIn > greenIn ? redIn > blueIn ? redIn : blueIn : greenIn > blueIn ? greenIn : blueIn;
min = redIn < greenIn ? redIn < blueIn ? redIn : blueIn : greenIn < blueIn ? greenIn : blueIn;
chroma = max - min;
if(chroma != 0)
{
if(max == redIn)
hue = ((greenIn - blueIn) / chroma) %6 ;
else if(max == greenIn)
hue = ((blueIn - redIn)/chroma) + 2;
else if(max == blueIn)
hue = ((redIn - greenIn)/chroma) + 4;
hue = (hue+20)%6;
if(chroma != 0)
saturation = chroma / max;
if(hue >= 0 && hue < 1)
{
redOut = chroma + max - chroma;
greenOut = chroma * (1 - abs((hue % 2) - 1)) + max - chroma;
blueOut = 0 + max - chroma;
}
else if(hue >= 1 && hue < 2)
{
redOut = chroma * (1 - abs((hue % 2) - 1)) + max - chroma;
greenOut = chroma + max - chroma;
blueOut = 0 + max - chroma;
}
else if(hue >= 2 && hue < 3)
{
redOut = 0 + max - chroma;
greenOut = chroma + max - chroma;
blueOut = chroma * (1 - abs((hue % 2) - 1)) + max - chroma;
}
else if(hue >= 3 && hue < 4)
{
redOut = 0 + max - chroma;
greenOut = chroma * (1 - abs((hue % 2) - 1)) + max - chroma;
blueOut = chroma + max - chroma;
}
else if(hue >= 4 && hue < 5)
{
redOut = chroma * (1 - abs((hue % 2) - 1)) + max - chroma;
greenOut = 0 + max - chroma;
blueOut = chroma + max - chroma;
}
else if(hue >= 5 && hue < 6)
{
redOut = chroma + max - chroma;
greenOut = 0 + max - chroma;
blueOut = chroma * (1 - abs((hue % 2) - 1)) + max - chroma;
}
}
//NSLog(#"redOut %u greenOut %u blueOut %u",redOut,greenOut,blueOut);
m_imageData[y*m_width+x]=redOut + greenOut + blueOut;
}
}
free(rgbImage);
// convert from a gray scale image back into a UIImage
uint8_t *result = (uint8_t *) calloc(m_width * m_height *sizeof(uint32_t), 1);
// process the image back to rgb
for(int i = 0; i < m_height * m_width; i++)
{
result[i*4]=0;
int val=m_imageData[i];
result[i*4+1]=val;
result[i*4+2]=val;
result[i*4+3]=val;
}
free(m_imageData);
// create a UIImage
colorSpace = CGColorSpaceCreateDeviceRGB();
context = CGBitmapContextCreate(result,
m_width,
m_height,
8,
m_width * sizeof(uint32_t),
colorSpace,
kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipLast
);
CGImageRef image = CGBitmapContextCreateImage(context);
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
#ifdef kNYXReturnRetainedObjects
UIImage* resultUIImage = [[UIImage alloc] initWithCGImage:image];
#else
UIImage *resultUIImage = [UIImage imageWithCGImage:image];
#endif
CGImageRelease(image);
free(result);
return resultUIImage;
but I'm not getting the polaroid image after execution this code.
What's the problem in this code or can you suggest me some other way.

Answer 1

The most obvious problem with the code is that, at the end of the method, you create a drawing context, do nothing in it, then take an image from it and return that as a UIImage. This will be blank, presumably. I think you're trying to obtain the image that is held in the data in result - I think you need to look at CGImageCreate instead rather than setting up a new context.
See here for information on creating a data provider with raw data, which you will need to pass to CGImageCreate. This all does look rather complicated.