Add write_to_csv template function implementation

Add write_to_csv template function implementation

Author: Jimmy-Hu

image_io.h

@@ -101,6 +101,56 @@ namespace TinyDIP
             }
         }
 
+        // -------------------------------------------------------------------------
+        // write_to_csv template function implementation (OpenMP Fallback)
+        // -------------------------------------------------------------------------
+        template<class ElementT = double>
+        requires TinyDIP::is_streamable<ElementT>
+        void write_to_csv(const char* const filename, const Image<ElementT>& input, const int precision = -1)
+        {
+            if (input.getDimensionality() != 2)
+            {
+                throw std::runtime_error("Input is not a 2D image!\n");
+            }
+
+            std::ofstream file(filename);
+            if (!file.is_open())
+            {
+                throw std::runtime_error("Could not open file for writing!\n");
+            }
+
+            const std::size_t height = input.getHeight();
+            const std::size_t width = input.getWidth();
+            
+            // Pre-allocate vector size to prevent race conditions
+            std::vector<std::string> row_strings(height);
+
+            #pragma omp parallel for
+            for (std::ptrdiff_t y = 0; y < static_cast<std::ptrdiff_t>(height); ++y)
+            {
+                std::ostringstream oss;
+                if (precision >= 0)
+                {
+                    oss << std::fixed << std::setprecision(precision);
+                }
+                
+                for (std::size_t x = 0; x < width; ++x)
+                {
+                    oss << input.at_without_boundary_check(x, static_cast<std::size_t>(y));
+                    if (x < width - 1)
+                    {
+                        oss << ",";
+                    }
+                }
+                row_strings[static_cast<std::size_t>(y)] = oss.str();
+            }
+
+            // Write appropriately sequenced rows into the target file
+            for (std::size_t y = 0; y < height; ++y)
+            {
+                file << row_strings[y] << '\n';
+            }
+        }
     }
 
     namespace pnm