Add a face detection example (#5)

examples/detect_faces/Cargo.toml

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+[package]
+name = "detect_faces"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+az_analyze_image = "0.1.1"
+image = "0.25.5"
+imageproc = "0.25.0"
+reqwest = "0.12.9"
+tokio = { version = "1.41.1", features = ["full"] }

examples/detect_faces/README.md

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+# Detect Faces
+
+> [!NOTE]
+> API Version 3.2
+
+## About
+
+In this example, the Analyze Image API is used to detect faces in an image.
+
+For each detected face, the API returns a **bounding box** (face rectangle),
+which defines a rectangle in the image.
+
+This example draws the bounding boxes on the image for all detected faces and
+saves it to `out.jpg`:
+
+<p align="center">
+  <img src="https://github.com/OTheDev/az_analyze_image/blob/main/examples/detect_faces/out.jpg?raw=true" />
+</p>
+
+## Image Source
+
+https://images.pexels.com/photos/1367269/pexels-photo-1367269.jpeg

examples/detect_faces/src/main.rs

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+/*
+Copyright 2024 Owain Davies
+SPDX-License-Identifier: Apache-2.0 OR MIT
+*/
+
+use az_analyze_image::v32::client::{AnalyzeImageOptions, Client};
+use az_analyze_image::v32::{FaceDescription, VisualFeatureTypes};
+
+use image::{load_from_memory_with_format, ImageFormat, Rgb, RgbImage};
+use imageproc::drawing::draw_hollow_rect_mut;
+use imageproc::rect::Rect;
+
+use reqwest::Client as ReqwestClient;
+
+use std::env::var;
+use std::error::Error;
+
+const IMAGE_URL: &str =
+    "https://images.pexels.com/photos/1367269/pexels-photo-1367269.jpeg";
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn Error>> {
+    let client: Client = get_client();
+
+    // Call the Analyze Image API with the face detection feature enabled
+    let faces: Vec<FaceDescription> = detect_faces(&client, IMAGE_URL).await?;
+
+    // Download the image bytes
+    let img_bytes: Vec<u8> = download_image(IMAGE_URL).await?;
+
+    // Load the image
+    let mut img: RgbImage =
+        load_from_memory_with_format(&img_bytes, ImageFormat::Jpeg)?.to_rgb8();
+
+    // Draw bounding boxes around all detected faces
+    draw_face_bounding_boxes(&mut img, &faces);
+
+    // Save the new image
+    img.save("out.jpg")?;
+
+    Ok(())
+}
+
+fn get_client() -> Client {
+    let key = var("CV_KEY").expect("no CV_KEY");
+    let endpoint = var("CV_ENDPOINT").expect("no CV_ENDPOINT");
+
+    Client::new(key, &endpoint).expect("failed to create client")
+}
+
+async fn detect_faces(
+    client: &Client,
+    url: &str,
+) -> Result<Vec<FaceDescription>, Box<dyn Error>> {
+    let features = vec![VisualFeatureTypes::Faces];
+    let options = AnalyzeImageOptions {
+        visual_features: Some(&features),
+        ..Default::default()
+    };
+
+    let analysis = client.analyze_image_url(url, options).await?;
+
+    Ok(analysis.faces.unwrap())
+}
+
+async fn download_image(url: &str) -> Result<Vec<u8>, Box<dyn Error>> {
+    let client = ReqwestClient::new();
+    let response = client.get(url).send().await?.bytes().await?;
+    Ok(response.to_vec())
+}
+
+fn draw_face_bounding_boxes(img: &mut RgbImage, faces: &[FaceDescription]) {
+    let thickness = 16;
+    let colors = [Rgb([1, 255, 79]), Rgb([0, 237, 245]), Rgb([118, 232, 181])];
+
+    for (i, face) in faces.iter().enumerate() {
+        let bounding_box = Rect::at(
+            face.face_rectangle.left as i32,
+            face.face_rectangle.top as i32,
+        )
+        .of_size(face.face_rectangle.width, face.face_rectangle.height);
+
+        let color = colors[i % colors.len()];
+
+        draw_thick_rect(img, bounding_box, color, thickness);
+    }
+}
+
+fn draw_thick_rect(
+    img: &mut RgbImage,
+    rect: Rect,
+    color: Rgb<u8>,
+    thickness: i32,
+) {
+    for i in 0..thickness {
+        let new_rect = Rect::at(rect.left() - i, rect.top() - i)
+            .of_size(rect.width() + i as u32 * 2, rect.height() + i as u32 * 2);
+
+        draw_hollow_rect_mut(img, new_rect, color);
+    }
+}