From 1dd06eb0da3fc96bc030c6bd0fb4584d220d71a2 Mon Sep 17 00:00:00 2001
From: Kumataro <Kumataro@users.noreply.github.com>
Date: Fri, 1 Aug 2025 09:49:43 +0900
Subject: [PATCH] imgcodecs: png: adjust value range for
 IMWRITE_PNG_ZLIBBUFFER_SIZE

---
 .../imgcodecs/include/opencv2/imgcodecs.hpp   |  2 +-
 modules/imgcodecs/src/grfmt_png.cpp           |  6 +++++-
 modules/imgcodecs/src/grfmt_spng.cpp          |  6 ++++++
 modules/imgcodecs/test/test_png.cpp           | 20 +++++++++++++++++++
 4 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/modules/imgcodecs/include/opencv2/imgcodecs.hpp b/modules/imgcodecs/include/opencv2/imgcodecs.hpp
index 039482017f..841d5b32cf 100644
--- a/modules/imgcodecs/include/opencv2/imgcodecs.hpp
+++ b/modules/imgcodecs/include/opencv2/imgcodecs.hpp
@@ -97,7 +97,7 @@ enum ImwriteFlags {
        IMWRITE_PNG_STRATEGY        = 17, //!< For PNG, One of cv::ImwritePNGFlags, default is IMWRITE_PNG_STRATEGY_RLE.
        IMWRITE_PNG_BILEVEL         = 18, //!< For PNG, Binary level PNG, 0 or 1, default is 0.
        IMWRITE_PNG_FILTER          = 19, //!< For PNG, One of cv::ImwritePNGFilterFlags, default is IMWRITE_PNG_FILTER_SUB.
-       IMWRITE_PNG_ZLIBBUFFER_SIZE = 20, //!< For PNG, sets the size of the internal zlib compression buffer in bytes.
+       IMWRITE_PNG_ZLIBBUFFER_SIZE = 20, //!< For PNG with libpng, sets the size of the internal zlib compression buffer in bytes, from 6 to 1048576(1024 KiB). Default is 8192(8 KiB). For normal use, 131072(128 KiB) or 262144(256 KiB) may be sufficient. If WITH_SPNG=ON, it is not supported.
        IMWRITE_PXM_BINARY          = 32, //!< For PPM, PGM, or PBM, it can be a binary format flag, 0 or 1. Default value is 1.
        IMWRITE_EXR_TYPE            = (3 << 4) + 0 /* 48 */, //!< override EXR storage type (FLOAT (FP32) is default)
        IMWRITE_EXR_COMPRESSION     = (3 << 4) + 1 /* 49 */, //!< override EXR compression type (ZIP_COMPRESSION = 3 is default)
diff --git a/modules/imgcodecs/src/grfmt_png.cpp b/modules/imgcodecs/src/grfmt_png.cpp
index 55e5f7ff11..4d3d8f9d8d 100644
--- a/modules/imgcodecs/src/grfmt_png.cpp
+++ b/modules/imgcodecs/src/grfmt_png.cpp
@@ -1007,7 +1007,11 @@ bool  PngEncoder::write( const Mat& img, const std::vector<int>& params )
                         break;
 
                     case IMWRITE_PNG_ZLIBBUFFER_SIZE:
-                        png_set_compression_buffer_size(png_ptr, params[i+1]);
+                        // The default value is 8 KiB.
+                        // The minimum limit is 6, which is from from https://github.com/opencv/opencv/blob/4.12.0/3rdparty/libpng/pngset.c#L1600 .
+                        // The maximum limit is 1 MiB, which has been provisionally set. libpng limitation is 2 GiB(INT32_MAX), but it is too large.
+                        // For normal use, 128 or 256 KiB may be sufficient. See https://zlib.net/zlib_how.html .
+                        png_set_compression_buffer_size(png_ptr, MIN(MAX(params[i+1],6), 1024*1024));
                         break;
 
                     default:
diff --git a/modules/imgcodecs/src/grfmt_spng.cpp b/modules/imgcodecs/src/grfmt_spng.cpp
index 8057af1222..e2f6f02bb9 100644
--- a/modules/imgcodecs/src/grfmt_spng.cpp
+++ b/modules/imgcodecs/src/grfmt_spng.cpp
@@ -23,6 +23,7 @@
 #include <zlib.h>
 
 #include "grfmt_spng.hpp"
+#include <opencv2/core/utils/logger.hpp>
 
 /*
  * libspng does not support RGB -> Gray conversion. In order to decode colorful images as grayscale
@@ -554,6 +555,11 @@ bool SPngEncoder::write(const Mat &img, const std::vector<int> &params)
                 filter = params[i+1];
                 set_filter = true;
             }
+            if( params[i] == IMWRITE_PNG_ZLIBBUFFER_SIZE )
+            {
+                // See https://libspng.org/docs/migrate-libpng/#miscellaneous-functions
+                CV_LOG_WARNING(nullptr, "libspng does not support png_set_compression_buffer_size() which is required for IMWRITE_PNG_ZLIBBUFFER_SIZE");
+            }
         }
 
         ihdr.bit_depth = depth == CV_8U ? isBilevel ? 1 : 8 : 16;
diff --git a/modules/imgcodecs/test/test_png.cpp b/modules/imgcodecs/test/test_png.cpp
index 0d2512fd20..967b852d76 100644
--- a/modules/imgcodecs/test/test_png.cpp
+++ b/modules/imgcodecs/test/test_png.cpp
@@ -569,6 +569,26 @@ INSTANTIATE_TEST_CASE_P(/**/,
         make_tuple("../perf/512x512.png", 8, 153708),
         make_tuple("../perf/512x512.png", 9, 152181)));
 
+// See https://github.com/opencv/opencv/issues/27614
+typedef testing::TestWithParam<int> Imgcodecs_Png_ZLIBBUFFER_SIZE;
+TEST_P(Imgcodecs_Png_ZLIBBUFFER_SIZE, encode_regression_27614)
+{
+    Mat img(320,240,CV_8UC3,cv::Scalar(64,76,43));
+    vector<uint8_t> buff;
+    bool status = false;
+    ASSERT_NO_THROW(status = imencode(".png", img, buff, { IMWRITE_PNG_ZLIBBUFFER_SIZE, GetParam() }));
+    ASSERT_TRUE(status);
+}
+
+INSTANTIATE_TEST_CASE_P(/*nothing*/, Imgcodecs_Png_ZLIBBUFFER_SIZE,
+                        testing::Values(5,
+                                        6,         // Minimum limit
+                                        8192,      // Default value
+                                        131072,    // 128 KiB
+                                        262144,    // 256 KiB
+                                        1048576,   // Maximum limit
+                                        1048577));
+
 #endif // HAVE_PNG
 
 }} // namespace