From 73839c499a6e2b9dd42b49b2e60432ddf663afd8 Mon Sep 17 00:00:00 2001
From: Even Rouault <even.rouault@spatialys.com>
Date: Sat, 28 Dec 2024 18:01:55 +0100
Subject: [PATCH] PNG: fix reading 16-bit interlaced images (on little-endian
 machines)

Fixes https://lists.osgeo.org/pipermail/gdal-dev/2024-December/059989.html
---
 autotest/gdrivers/data/png/uint16_interlaced.png | Bin 0 -> 775 bytes
 autotest/gdrivers/png.py                         |  10 ++++++++++
 frmts/png/pngdataset.cpp                         |  15 +++++++++++++++
 3 files changed, 25 insertions(+)
 create mode 100644 autotest/gdrivers/data/png/uint16_interlaced.png

diff --git a/autotest/gdrivers/data/png/uint16_interlaced.png b/autotest/gdrivers/data/png/uint16_interlaced.png
new file mode 100644
index 0000000000000000000000000000000000000000..a8888de766b77915f0745bf178f1c8edc201bd69
GIT binary patch
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diff --git a/autotest/gdrivers/png.py b/autotest/gdrivers/png.py
index 7260ec251484..70c1688806aa 100755
--- a/autotest/gdrivers/png.py
+++ b/autotest/gdrivers/png.py
@@ -471,3 +471,13 @@ def test_png_copy_mdd():
     ds = None
 
     gdal.Unlink(filename)
+
+
+###############################################################################
+# Read test of 16-bit interlaced
+
+
+def test_png_read_interlace_16_bit():
+
+    ds = gdal.Open("data/png/uint16_interlaced.png")
+    assert ds.GetRasterBand(1).Checksum() == 4672
diff --git a/frmts/png/pngdataset.cpp b/frmts/png/pngdataset.cpp
index 1f1fe174730b..cfe5981879c6 100644
--- a/frmts/png/pngdataset.cpp
+++ b/frmts/png/pngdataset.cpp
@@ -1405,6 +1405,21 @@ CPLErr PNGDataset::LoadInterlacedChunk(int iLine)
 
     bool bRet = safe_png_read_image(hPNG, png_rows, sSetJmpContext);
 
+    // Do swap on LSB machines. 16-bit PNG data is stored in MSB format.
+#ifdef CPL_LSB
+    if (bRet && nBitDepth == 16)
+    {
+        for (int i = 0; i < GetRasterYSize(); i++)
+        {
+            if (i >= nBufferStartLine && i < nBufferStartLine + nBufferLines)
+            {
+                GDALSwapWords(png_rows[i], 2,
+                              GetRasterXSize() * GetRasterCount(), 2);
+            }
+        }
+    }
+#endif
+
     CPLFree(png_rows);
     CPLFree(dummy_row);
     if (!bRet)