quantization matrix wip

src/bin/dctfilename.rs

@@ -18,7 +18,7 @@ impl Cfg{
 
 fn main() {
     //Init all descriptors:
-    let desc = DCT;
+    let desc = DCT::new();
 
     let args: Vec<String> = env::args().collect();
     //dbg!(args);

src/descriptors.rs

@@ -45,14 +45,76 @@ impl Descriptor for Median {
     }
 }
 
-pub struct DCT;
+/// A struct representing a Discrete Cosine Transform descriptor
+/// Transforms an image into an 8x8 grayscale version, and transforms it
+/// into the frequency domain
+pub struct DCT {
+    quantization_matrix: [u8; 64],
+}
+
+
+/// Interprets a 64-element array as an 8x8 matrix
+/// returns a nicely printable string
+fn print_matrix<T: ToString>(array: [T; 64]) -> String {
+    let mut output = String::new();
+    for x in 0..8 {
+        for y in 0..8 {
+            output.push_str(&array[x*8+y].to_string());
+            output.push_str(",\t");
+        }
+        output.push('\n');
+    }
+    output
+}
+
+
+// Define S such that if (Q < 50), then S = 5000/Q, else S = 200 – 2*Q.
+// The output quantization matrix Ts[i,j] at each location of row i and column j is such that 
+// Ts[i,j] = floor((S * Tb[i,j] + 50) / 100)
+
+
+impl DCT {
+    pub fn new() -> DCT {
+        let base_quantization_matrix: [u8; 64] = [
+            16, 11, 10, 16, 24, 40, 51, 61,
+            12, 12, 14, 19, 26, 58, 60, 55,
+            14, 13, 16, 24, 40, 57, 69, 56,
+            14, 17, 22, 29, 51, 87, 80, 62,
+            18, 22, 37, 56, 6, 10, 103, 77,
+            24, 35, 55, 64, 8, 10, 113, 92,
+            49, 64, 78, 8, 10, 12, 12, 101,
+            72, 92, 95, 9, 11, 10, 103, 99,
+        ];
+        DCT { quantization_matrix: base_quantization_matrix }
+    }
+    pub fn quantization_matrix(&self, quality: u8) -> [u8; 64] {
+        let mut quantization_matrix = self.quantization_matrix.clone();
+        let scalar: f32 = match quality {
+            1..=49 => 5000.0/quality as f32,
+            50..=100 => 200.0 - 2.0*quality as f32,
+            _ => 1.0 //TODO: error
+        };
+        for i in 0..64 {
+            quantization_matrix[i] = ((scalar * self.quantization_matrix[i] as f32 + 50.0) / 100.0).floor() as u8;
+            if quantization_matrix[i] == 0 {
+                quantization_matrix[i] = 1;
+            }
+        }
+        quantization_matrix
+    }
+}
 
 impl Descriptor for DCT {
     fn describe(&self, img: image::DynamicImage) -> u64 {
+        let quality: u8 = 15;
+        let qmatrix = self.quantization_matrix(quality);
+
+        println!("Base quantization matrix:\n{}", print_matrix(self.quantization_matrix));
+        println!("Q-{} quantization matrix:\n{}", quality, print_matrix(qmatrix));
         let mut dct_values: [f64; 64] = [0.0; 64];
         let mut reconstructed: [u8; 64] = [0; 64];
         let img = self.resize(img);
-        let _ = img.save("resize.png").expect("Error saving file");
+        img.save("resize.png").expect("Error saving file");
         for u in 0..8 {
             for v in 0..8 {
                 let k = (v*8)+u;
@@ -79,6 +141,17 @@ impl Descriptor for DCT {
                 //println!{"{}", dct_values[k]}
             }
         }
+        println!("DCT-coefficients:\n {}", print_matrix(dct_values));
+        // Quantization:
+        for i in 0..64 {
+            dct_values[i] = (dct_values[i] / qmatrix[i] as f64).round();
+        }
+        println!("DCT-coefficients, quantized:\n {}", print_matrix(dct_values));
+        // De-quantization:
+        for i in 0..64 {
+            dct_values[i] = dct_values[i] * qmatrix[i] as f64;
+        }
+        println!("DCT-coefficients, de-quantized:\n {}", print_matrix(dct_values));
         for k in 0..64  {
             let x = (k%8) as f64;
             let y = (k/8) as f64;
@@ -106,6 +179,7 @@ impl Descriptor for DCT {
             //println!("Reconstructed pixel: {}", sum);
             reconstructed[k] = std::cmp::min(255_u8, sum as u8);
         }
+        //println!("{}", print_matrix(reconstructed));
         save_buffer(
             "reconstructed.png",
             &reconstructed,