Question

When sharing an image in an iPhone, we are given an opportunity to pick different sizes of an image – Small, Medium, Large, Original. And an opportunity of see the size in KB/MB along with each classification.

1. Where does apple expose this code for users to leverage? I couldn’t spot it in my searches in iOS docs.
2. What are some tested & tried frameworks/methods available on GitHub or elsewhere that can emulate this behavior?

EDITED:
I evaluated the solution posted by Brad Larson:
UIImage: Resize, then Crop
By confirming a decrease in size via the size measuring solution given below.
Together they are a good fit.

Answer 1

1. Where does apple expose this code for users to leverage? I couldn’t spot it in my searches in iOS docs.

iOS is not open-source project. Apple releases only sample code which is used like tutorial sample project.

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Here’s an article regarding calcutation of image file size.

This is very simple, though. Here’s the code:

UIImage *image = [UIImage imageNamed:@"your_big_image.png"];

size_t depth = CGImageGetBitsPerPixel(image.CGImage);
size_t width = CGImageGetWidth(image.CGImage);
size_t height = CGImageGetHeight(image.CGImage);

double bytes = ((double)width * (double)height * (double)depth) / 8.0;

Now you have your image size in bytes.

To convert it to kB divide it by 1024. If you want to get MB, divide by 1048576 (1024×1024).

double kb = bytes / 1024.0f;
double mb = bytes / 1048576.0f

Then you can display it to your user by formatting your message as following:

NSString *msg = [NSString stringWithFormat:@"Original %dx%d (%.2f MB)", (int)width,(int)height, (float)mb];