How to combine large JPEG's in Cocoa Mac application - objective-c

Question

In our Mac application built in Cocoa, we would like to combine 5 large JPEG images into one JPEG. We have the following images:
1.jpeg 50000px wide X 5000px high
2.jpeg 50000px wide X 5000px high
3.jpeg 50000px wide X 5000px high
4.jpeg 50000px wide X 5000px high
5.jpeg 50000px wide X 5000px high
We would like to combine these images one above the other to form an output jpeg:
50000px wide X 25000px high
The problem is that the resulting JPEG is very large and this results in memory issues when we use the following approach to make output JPEG.
NSRect imageRect = NSMakeRect(0.0, 0.0, 50000, 25000);
NSBitmapImageRep *savedImageBitmapRep = [[NSBitmapImageRep alloc]
initWithBitmapDataPlanes:nil
pixelsWide:imageRect.size.width
pixelsHigh:imageRect.size.height
bitsPerSample:8
samplesPerPixel:4
hasAlpha:YES
isPlanar:NO
colorSpaceName:NSCalibratedRGBColorSpace
bitmapFormat:0
bytesPerRow:(4 * imageRect.size.width)
bitsPerPixel:32];
[NSGraphicsContext saveGraphicsState];
[NSGraphicsContext
setCurrentContext:[NSGraphicsContext graphicsContextWithBitmapImageRep:
savedImageBitmapRep]];
// Read 1.jpeg, 2.jpeg, 3.jpeg, 4.jpeg, 5.jpeg as NSImage
// and draw them on the current context in their respective location
[NSGraphicsContext restoreGraphicsState];
NSMutableData *imageData = [NSMutableData data];
CGImageDestinationRef imageDest = CGImageDestinationCreateWithData(
(__bridge CFMutableDataRef)imageData, kUTTypeJPEG, 1, NULL);
CGImageDestinationAddImage(imageDest, [savedImageBitmapRep CGImage],
(__bridge CFDictionaryRef)properties);
CGImageDestinationFinalize(imageDest);
if (imageDest != NULL) {
CFRelease(imageDest);
}
//write imageData to a JPEG file
How can we achieve our objective without facing memory issues?

Answer 1

"Memory issues" is vague but I assume you simply mean that you want to avoid the 4.5+ GBs of memory required to hold 50,000 x 25,000 pixels.
The only way to avoid that is to drop down to a lower level API which lets you encode each MCU row (each 8 or 16 rows of pixels) separately at a time. libjpeg supports this, for example. You would load and render the minimum required data to produce such a row with whatever minimum memory constraints you have in mind, and then pass that row off to the encoder, before moving to the next row.

Answer 2

You can resize them to be smaller for displaying. but only when saving/storing you can directly store all the sizes