Improve Performance by 56% by Replacing Library

Background

I have a side project called “comics.” It’s a simple HTTP server that serves comics so I can access them anywhere. According to the Chrome documentation, to make images lazy-loaded, the server needs to run an initial scan and retrieve the dimensions of images when it starts. However, its performance is poor on my NAS, which uses HDD drives.

Initially, I used the image-rs library, which I found widely recommended online.

Benchmark

After adding tracing to my code, I discovered that retrieving image dimensions during the initial scan took most of the time, which makes sense since it’s the server’s main task during this phase. However, I noticed the server’s performance varies with the size of the images. Digging deeper, I found that the performance of image-rs degrades as image size increases. Here’s a code snippet that shows this issue:

# Cargo.toml
[package]
name = "a"
version = "0.1.0"
edition = "2021"

[dependencies]
image = { version = "0.25.1", default-features = false, features = ["jpeg"] }

// src/main.rs
use image::GenericImageView;
use std::env;

fn main() {
    let args: Vec<String> = env::args().collect();
    let image_path = args.get(1).expect("exepct file path");
    let img = image::open(image_path).expect("failed to open image");
    let (width, height) = img.dimensions();
    println!("{}x{}", width, height);
}

We can download sample images from Lorem Picsum using the following curl command:

curl -L https://picsum.photos/100/100 > 100.jpg
curl -L https://picsum.photos/1000/1000 > 1000.jpg

Then, benchmark image-rs with hyperfine:

$ cargo build --release # build the example with release profile
$ inxi -b # show my CPU
...
CPU:       Info: 6-Core AMD Ryzen 5 5600X [MT MCP] speed: 3693 MHz
...
$ hyperfine './target/release/a 100.jpg' './target/release/a 1000.jpg'

Here are the results:

But I needed more proof, so I looked into the source code of image-rs and found that it loads the entire image into memory to fetch the dimensions.

let mut r = r;
r.read_to_end(&mut input)?; // 👈
let mut decoder = zune_jpeg::JpegDecoder::new(input.as_slice());
decoder.decode_headers().map_err(ImageError::from_jpeg)?;
let (width, height) = decoder.dimensions().unwrap();

To be fair, image-rs is a feature-rich library, but it doesn’t meet my performance expectations. So, I searched further and found an interesting topic on Stack Overflow:

Get Image size WITHOUT loading image into memory

This led me to a Rust library called imsz-rs. I ran a simple benchmark comparing image-rs and imsz, and the performance of imsz remained consistent even with larger images:

# Cargo.toml
[package]
name = "b"
version = "0.1.0"
edition = "2021"

[dependencies]
imsz = "0.3.1"

use std::env;

fn main() {
    let args: Vec<String> = env::args().collect();
    let image_path = args.get(1).expect("exepct file path");
    let info = imsz::imsz_from_path(image_path).expect("failed to get dimensions");
    println!("{}x{}", info.width, info.height);
}

As the results show, imsz performs consistently regardless of the image size.

I tried to understand how imsz gets the dimensions of an image, but it looks like I need to know about the JPEG format. To me, it just seems like looking for and reading specific bytes. All I can do is appreciate the maintainer’s work.

Results

Here are the results of benchmarking image-rs and imsz:

As expected, imsz outperforms image-rs.

As the results show, no matter how big the image is, imsz performs consistently. Finally, I replaced image-rs with imsz and saw a 56% performance improvement on my NAS.

Closing Words

In conclusion, it’s always rewarding to dig deeper to improve performance. By switching from image-rs to imsz, I achieved a significant performance boost. Exploring and understanding the underlying code can lead to substantial improvements.