Merge pull request OSGeo#11553 from rouault/png_16bit_interlaced

PNG: fix reading 16-bit interlaced images (on little-endian machines)
innFactory · Dec 28, 2024 · a6fed4d · a6fed4d
2 parents 8d5ca35 + 73839c4
commit a6fed4d
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diff --git a/autotest/gdrivers/data/png/uint16_interlaced.png b/autotest/gdrivers/data/png/uint16_interlaced.png
diff --git 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
@@ -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)