From 659b53ed5cba9a17b7b1724fcba17031aa2a835a Mon Sep 17 00:00:00 2001
From: Mark Hoekveen <mark@hoekveen.net>
Date: Sun, 12 May 2024 14:37:41 +0200
Subject: [PATCH] DCT mask calculation updated

---
 src/bin/dctfilename.rs |  2 +-
 src/descriptors/dct.rs | 66 +++++++++++++++++++++++++++++++++++++-----
 2 files changed, 59 insertions(+), 9 deletions(-)

diff --git a/src/bin/dctfilename.rs b/src/bin/dctfilename.rs
index 931ced6..0641c45 100644
--- a/src/bin/dctfilename.rs
+++ b/src/bin/dctfilename.rs
@@ -33,7 +33,7 @@ fn main() {
         .expect("Unable to open file");
     let phash: u64 = desc.describe(&img);
     debug!("Phash integer:\n{phash}");
-    debug!("Phash binary:\n{phash:b}");
+    debug!("Phash binary:\n{phash:064b}");
     let output = URL_SAFE_NO_PAD.encode(phash.to_be_bytes());
     println!("{output}")
 }
diff --git a/src/descriptors/dct.rs b/src/descriptors/dct.rs
index 1244af9..d6835fa 100644
--- a/src/descriptors/dct.rs
+++ b/src/descriptors/dct.rs
@@ -107,7 +107,7 @@ impl Descriptor for DCT {
         debug!("DCT-coefficients:\n {}", print_matrix(dct_values));
 
         // Quantization:
-        debug!("Using quantization matrix:\n{}", print_matrix(self.quantization_matrix));
+        //debug!("Using quantization matrix:\n{}", print_matrix(self.quantization_matrix));
         for i in 0..64 {
             dct_values[i] = (dct_values[i] / self.quantization_matrix[i] as f64).round();
         }
@@ -119,11 +119,10 @@ impl Descriptor for DCT {
             for i in 0..64 {
                 dct_values[i] = dct_values[i] * self.quantization_matrix[i] as f64;
             }
-            debug!("DCT-coefficients, de-quantized:\n {}", print_matrix(dct_values));
+            //debug!("DCT-coefficients, de-quantized:\n {}", print_matrix(dct_values));
 
             // Reconstruction original pixel values:
             let reconstructed = self.idct(dct_values);
-            debug!("Reconstructed pixel values:\n{}", print_matrix(reconstructed));
 
             save_buffer(
                 "reconstructed.png",
@@ -135,13 +134,64 @@ impl Descriptor for DCT {
         }
 
         // Calculating descriptor from dct values:
-        let mut mask: u64 = 0;
-        for dct in dct_values {
-            if dct > 0.0 {
-                mask += 1
+
+        // Zigzag order for our flattened array,
+        // first 28 elements only
+        let zigzag: [usize; 28] = [
+            0, 
+            1, 8,
+            16, 9, 2,
+            3, 10, 17, 24,
+            32, 25, 18, 11, 4,
+            5, 12, 19, 26, 33, 40,
+            48, 41, 34, 27, 20, 13, 6,
+        ];
+
+        // Mask that indicates if a dct coefficient is positive or negative
+        // By convention, when sign bit is 1, number is negative
+        let mut sign_mask: u64 = 0;
+        // If first horizontal AC coefficient is negative
+        // This might account for horizontal flips when applied to all horizontal coefficients.
+        let sign_mult = dct_values[1].signum();
+
+        // Mask that indicates if a coefficient is bigger or smaller than previous in order
+        let mut pearson_mask: u64 = 0;
+        let mut prev = dct_values[0];
+
+
+        for i in zigzag {
+            let cur = dct_values[i];
+            if cur > prev {
+                pearson_mask += 1;
             }
-            mask = mask << 1;
+            prev = cur;
+
+            let signum = dct_values[i].signum();
+            // Only multiply sign if dct-coefficient contains a horizontal component.
+            if 
+                i % 8 != 0 && sign_mult * signum < 0.0
+                ||
+                signum < 0.0
+            {
+                sign_mask += 1;
+            }
+
+            // Shift masks
+            sign_mask = sign_mask << 1;
+            pearson_mask = pearson_mask << 1;
         }
+        debug!("Sign    mask: {:028b}", sign_mask);
+        debug!("Pearson mask: {:028b}", pearson_mask);
+
+        let mut mask = sign_mask;
+        debug!("Mask: {:064b}", mask);
+        mask = mask << 28;
+        debug!("Mask: {:064b}", mask);
+        mask += pearson_mask;
+        debug!("Mask: {:064b}", mask);
+        mask = mask << 8;
+        debug!("Mask: {:064b}", mask);
+        // TODO: Do something with these last 8 bits.
         mask
     }
 }
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