Question

I need to extract the raw RGB bitmap data from a JPEG or PNG file, with all the bits in the file, not a window or color converted version.

I’m new to Cocoa, but it looks like I open an image using NSImage like this:

NSString* imageName=[[NSBundle mainBundle] pathForResource:@"/Users/me/Temp/oxberry.jpg" ofType:@"JPG"];
NSImage*  tempImage=[[NSImage alloc] initWithContentsOfFile:imageName];
NSBitmapImageRep* imageRep=[[[NSBitmapImageRep alloc] initWithData:[tempImage TIFFRepresentation]] autorelease];
unsigned char* bytes=[imageRep bitmapData];
int bits=[imageRep bitsPerPixel];

Then to get the bitmap data there seems to be lots of options: Bitmapimage, CGImage, etc.

What is the simplest approach and if there was a code snippet, that would be great.

Thanks!

Answer 1

You’re on the right track. As you noticed, there are lot of ways to do this.

Once you have an NSImage, you can create a bitmap representation, and access its bytes directly. An easy way to get a NSBitmapImageRep is to do this:

NSBitmapImageRep* imageRep = [[[NSBitmapImageRep alloc] initWithData:[tempImage TIFFRepresentation]] autorelease];

unsigned char* bytes = [imageRep bitmapData];
int bitsPerPixel  = [imageRep bitsPerPixel];
// etc

Going through the TIFFRepresentation step is safer than accessing the NSImage’s representations directly.