Create greyscale example

examples/greyscale.rs

@@ -0,0 +1,34 @@
+use ccvl::image::*;
+
+fn filter(img: Image<SRGBA>) -> Image<SRGBA> {
+    img.map(|p| Luminance::from(p).into())
+}
+
+fn main() -> std::process::ExitCode {
+    let args = std::env::args().collect::<Vec<String>>();
+    if args.len() != 3 {
+        println!("Usage: {} IN OUT", args[0].as_str());
+        return std::process::ExitCode::FAILURE;
+    }
+
+    let input_path = args[1].as_str();
+    let output_path = args[2].as_str();
+
+    match Image::load::<Farbfeld>(input_path) {
+        Err(Error::Invalid) => {
+            println!("{} is not a valid image", input_path);
+            std::process::ExitCode::FAILURE
+        }
+        Err(Error::Io(err)) => {
+            println!("I/O error loading image {}: {}", input_path, err);
+            std::process::ExitCode::FAILURE
+        }
+        Ok(img) => match filter(img).save::<Farbfeld>(output_path) {
+            Err(err) => {
+                println!("I/O error saving image {}: {}", output_path, err);
+                std::process::ExitCode::FAILURE
+            }
+            Ok(()) => std::process::ExitCode::SUCCESS,
+        },
+    }
+}