How to create and retrieve new bitmap in iOS

Question

I would like to convert an Image from one format(.png) to other image format (.img format). I was able to retrieve and modify the rgba values for the same image format.Is there any additional thing I need to do to convert it to other image formats?

I created an empty bitmap and would like to draw the to image this bitmap.

CGImageRef cgimage = image.CGImage;

size_t width  = CGImageGetWidth(cgimage);
size_t height = CGImageGetHeight(cgimage);

size_t bytesPerRow = CGImageGetBytesPerRow(cgimage);
size_t bytesPerPixel = CGImageGetBitsPerPixel(cgimage);
size_t bitsPerComponent = CGImageGetBitsPerComponent(cgimage);
size_t bytes_per_pixel = bytesPerPixel / bitsPerComponent;

CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(cgimage);

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
unsigned char *rawData = malloc(height * width * 4);
memset(rawData, 0, height * width * 4);

CGContextRef context = CGBitmapContextCreate(rawData, width, height, bitsPerComponent, bytesPerRow, colorSpace, bitmapInfo);

CGContextDrawImage(context, CGRectMake(0, 0, width, height), image.CGImage);

Are there any functions in iOS to fill the output bitmap with modified rgba values.

What do you mean by "How to draw data to Bitmap in iOS"? Are you talking about pixel-picking a color at a specific point? — El Tomato, Apr 15 '13 at 11:17
The more I read, the more I get confused. One of the extensions you indicate (.img) was used till a decade ago or so as a disc image format. — El Tomato, Apr 15 '13 at 11:30

score 3 · Accepted Answer · answered Apr 15 '13 at 11:15

It would look something like this:

UIImage *image = self.theImage;
CGImageRef imageRef = [image CGImage];
NSUInteger width = CGImageGetWidth(imageRef);
NSUInteger height = CGImageGetHeight(imageRef);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
NSMutableData *data = [[NSMutableData alloc] initWithCapacity:height * width * 4];
unsigned char *rawData = data.mutableBytes;
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;
CGContextRef context = CGBitmapContextCreate(rawData, width, height,
                                             bitsPerComponent, bytesPerRow, colorSpace,
                                             kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorSpace);

CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
CGContextRelease(context);

int byteIndex = (bytesPerRow * 0) + 0 * bytesPerPixel;

If you want to manipulate the data, you iterate through byteIndex . Hope that's what you are looking for.

How to create and retrieve new bitmap in iOS

1 Answers1