From 56b94542a69cabe8a1795bf26da679f829e61c0e Mon Sep 17 00:00:00 2001
From: Felix Hanau <hanau2@illinois.edu>
Date: Thu, 27 Jun 2019 18:44:34 +0100
Subject: [PATCH] Fix decoding interlaced images with height or width <= 2
 (#175)

---
 src/png/scan_lines.rs     |  28 +++++++++++++++++++++-------
 tests/files/issue-175.png | Bin 0 -> 71 bytes
 tests/regression.rs       |  12 ++++++++++++
 3 files changed, 33 insertions(+), 7 deletions(-)
 create mode 100644 tests/files/issue-175.png

diff --git a/src/png/scan_lines.rs b/src/png/scan_lines.rs
index 38f98e0f..8cd7e1b9 100644
--- a/src/png/scan_lines.rs
+++ b/src/png/scan_lines.rs
@@ -97,6 +97,8 @@ impl Iterator for ScanLineRanges {
         let (pixels_per_line, current_pass) = if let Some(ref mut pass) = self.pass {
             // Scanlines for interlaced PNG files
             // Handle edge cases for images smaller than 5 pixels in either direction
+            // No extra case needed for skipping pass 7 as this is already handled by the
+            // self.left == 0 check above
             if self.width < 5 && pass.0 == 2 {
                 pass.0 = 3;
                 pass.1 = 4;
@@ -106,13 +108,25 @@ impl Iterator for ScanLineRanges {
                 pass.0 = 4;
                 pass.1 = 0;
             }
-            let (pixels_factor, y_steps) = match pass {
-                (1, _) | (2, _) => (8, 8),
-                (3, _) => (4, 8),
-                (4, _) => (4, 4),
-                (5, _) => (2, 4),
-                (6, _) => (2, 2),
-                (7, _) => (1, 2),
+            if self.width < 3 && pass.0 == 4 {
+                pass.0 = 5;
+                pass.1 = 2;
+            }
+            if self.height < 3 && pass.0 == 5 {
+                pass.0 = 6;
+                pass.1 = 0;
+            }
+            if self.width == 1 && pass.0 == 6 {
+                pass.0 = 7;
+                pass.1 = 1;
+            }
+            let (pixels_factor, y_steps) = match pass.0 {
+                1 | 2 => (8, 8),
+                3 => (4, 8),
+                4 => (4, 4),
+                5 => (2, 4),
+                6 => (2, 2),
+                7 => (1, 2),
                 _ => unreachable!(),
             };
             let mut pixels_per_line = self.width / pixels_factor as u32;
diff --git a/tests/files/issue-175.png b/tests/files/issue-175.png
new file mode 100644
index 0000000000000000000000000000000000000000..10d480005ddd55a1220067a84a00d73a1c5af6a6
GIT binary patch
literal 71
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TTM3;3$}o7k`njxgN@xNAnO_bW

literal 0
HcmV?d00001

diff --git a/tests/regression.rs b/tests/regression.rs
index 1b20edee..a5d8bd39 100644
--- a/tests/regression.rs
+++ b/tests/regression.rs
@@ -623,3 +623,15 @@ fn issue_171() {
         BitDepth::Eight,
     );
 }
+
+#[test]
+fn issue_175() {
+    test_it_converts(
+        "tests/files/issue-175.png",
+        None,
+        ColorType::Grayscale,
+        BitDepth::One,
+        ColorType::Grayscale,
+        BitDepth::One,
+    );
+}
\ No newline at end of file