implement png read routines

crates/kornia-io/Cargo.toml

@@ -16,6 +16,7 @@ all-features = true
 [dependencies]
 image = "0.25"
 kornia-image = { workspace = true }
+png = "0.17"
 log = { workspace = true }
 thiserror = { workspace = true }
 

crates/kornia-io/src/error.rs

@@ -25,4 +25,8 @@ pub enum IoError {
     /// Error to decode the image.
     #[error("Failed to decode the image")]
     ImageDecodeError(#[from] image::ImageError),
+
+    /// Error to decode the PNG image.
+    #[error("Failed to decode the image")]
+    PngDecodeError(String),
 }

crates/kornia-io/src/lib.rs

@@ -14,6 +14,9 @@ pub mod functional;
 #[cfg(feature = "jpegturbo")]
 pub mod jpeg;
 
+/// PNG image encoding and decoding.
+pub mod png;
+
 /// GStreamer video module for real-time video processing.
 #[cfg(feature = "gstreamer")]
 pub mod stream;

crates/kornia-io/src/png.rs

@@ -0,0 +1,113 @@
+use std::{fs::File, path::Path};
+
+use kornia_image::Image;
+use png::Decoder;
+
+use crate::error::IoError;
+
+/// Read a PNG image with a single channel (mono8).
+///
+/// # Arguments
+///
+/// * `file_path` - The path to the PNG file.
+///
+/// # Returns
+///
+/// A grayscale image with a single channel (mono8).
+pub fn read_image_png_mono8(file_path: impl AsRef<Path>) -> Result<Image<u8, 1>, IoError> {
+    let (buf, size) = read_png_impl(file_path)?;
+    Ok(Image::new(size.into(), buf)?)
+}
+
+/// Read a PNG image with a three channels (rgb8).
+///
+/// # Arguments
+///
+/// * `file_path` - The path to the PNG file.
+///
+/// # Returns
+///
+/// A RGB image with three channels (rgb8).
+pub fn read_image_png_rgb8(file_path: impl AsRef<Path>) -> Result<Image<u8, 3>, IoError> {
+    let (buf, size) = read_png_impl(file_path)?;
+    Ok(Image::new(size.into(), buf)?)
+}
+
+/// Read a PNG image with a four channels (rgba8).
+///
+/// # Arguments
+///
+/// * `file_path` - The path to the PNG file.
+///
+/// # Returns
+///
+/// A RGBA image with four channels (rgba8).
+pub fn read_image_png_rgba8(file_path: impl AsRef<Path>) -> Result<Image<u8, 4>, IoError> {
+    let (buf, size) = read_png_impl(file_path)?;
+    Ok(Image::new(size.into(), buf)?)
+}
+
+/// Read a PNG image with a single channel (mono16).
+///
+/// # Arguments
+///
+/// * `file_path` - The path to the PNG file.
+///
+/// # Returns
+///
+/// A grayscale image with a single channel (mono16).
+pub fn read_image_png_mono16(file_path: impl AsRef<Path>) -> Result<Image<u16, 1>, IoError> {
+    let (buf, size) = read_png_impl(file_path)?;
+
+    // convert the buffer to u16
+    let mut buf_u16 = Vec::with_capacity(buf.len() / 2);
+    for chunk in buf.chunks_exact(2) {
+        buf_u16.push(u16::from_be_bytes([chunk[0], chunk[1]]));
+    }
+
+    Ok(Image::new(size.into(), buf_u16)?)
+}
+
+// utility function to read the png file
+fn read_png_impl(file_path: impl AsRef<Path>) -> Result<(Vec<u8>, [usize; 2]), IoError> {
+    // verify the file exists
+    let file_path = file_path.as_ref();
+    if !file_path.exists() {
+        return Err(IoError::FileDoesNotExist(file_path.to_path_buf()));
+    }
+
+    // verify the file extension
+    if let Some(extension) = file_path.extension() {
+        if extension != "png" {
+            return Err(IoError::InvalidFileExtension(file_path.to_path_buf()));
+        }
+    } else {
+        return Err(IoError::InvalidFileExtension(file_path.to_path_buf()));
+    }
+
+    let file = File::open(file_path)?;
+    let mut reader = Decoder::new(file)
+        .read_info()
+        .map_err(|e| IoError::PngDecodeError(e.to_string()))?;
+
+    let mut buf = vec![0; reader.output_buffer_size()];
+    let info = reader
+        .next_frame(&mut buf)
+        .map_err(|e| IoError::PngDecodeError(e.to_string()))?;
+
+    Ok((buf, [info.width as usize, info.height as usize]))
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::error::IoError;
+    use crate::png::read_image_png_mono8;
+
+    #[test]
+    fn read_png_mono8() -> Result<(), IoError> {
+        let image = read_image_png_mono8("../../tests/data/dog.png")?;
+        assert_eq!(image.size().width, 258);
+        assert_eq!(image.size().height, 195);
+        Ok(())
+    }
+}