How to programmatically change contrast of PNG image of without background in iPhone objective-c?

Question

I want to programmatically change the contrast of a PNG image which has no background or I must say transparent background. The below image shows the example.

I am able to change the contrast of with background image. But not able to change it in without background. I have tried this and this But both works in with background Image. Please help me to achieve this or suggest me any solution or tutorial link.

Thanks in advance

Answer 1

CGImageRef inImage = self.CGImage;
CFDataRef m_DataRef = CGDataProviderCopyData(CGImageGetDataProvider(inImage));  
UInt8 * m_PixelBuf = (UInt8 *) CFDataGetBytePtr(m_DataRef);  

int length = CFDataGetLength(m_DataRef);

for (int i=0; i<length; i+=4)
{
    filter(m_PixelBuf,i,context);
}  
CGContextRef ctx = CGBitmapContextCreate(m_PixelBuf,  
                                         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);
return finalImage;