Added convenience function to Rawtile class to duplicate bands for encoders that cannot natively handle single band monochrome images: simplifies WebP encoding

Author: ruven

ChangeLog

@@ -1,3 +1,8 @@
+05/09/2024:
+	- Added convenience function to Rawtile class to duplicate bands for encoders that cannot natively handle
+	  single band monochrome images: simplifies WebP encoding.
+
+
 29/06/2024:
 	- Updated autoconf tiff m4 to search for tiffio.h rather than just tiff.h when using TIFFOpen().
 	- Switched metadata assignment within input image classes to use more efficient map insert() syntax.

src/RawTile.h

@@ -2,7 +2,7 @@
 
 /*  IIPImage Server
 
-    Copyright (C) 2000-2023 Ruven Pillay.
+    Copyright (C) 2000-2024 Ruven Pillay.
 
     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
@@ -271,7 +271,7 @@ class RawTile {
     unsigned char* src_ptr = (unsigned char*) buffer;
     unsigned char* dst_ptr = (unsigned char*) data;
 
-    // Copy one scanline at a time
+    // Copy one entire scanline at a time
     unsigned int dlen = w * channels * (bpc/8);
     unsigned int slen = width * channels * (bpc/8);
 
@@ -293,6 +293,44 @@ class RawTile {
 
 
 
+  /// Expand monochrome 1 band image to 3 by duplicating channels 
+  void triplicate() {
+
+    if( channels != 1 ) return;
+
+    // Keep track of original data buffer and whether we manage it
+    void* buffer = data;
+    int mm = memoryManaged;
+
+    // Create a new buffer with the new size - make sure we update channel number first
+    channels = 3;
+    allocate();
+
+    // Loop through each pixel and duplicate
+    unsigned int len = width * height;
+    uint32_t n = 0;
+    for( uint32_t i=0; i<len; i++ ){
+      for( uint8_t k=0; k<3; k++ ){
+	if( bpc == 32 ){
+	  if( sampleType == SampleType::FLOATINGPOINT ) ((float*) data)[n+k] = ((float*) buffer)[i];
+	  else               ((unsigned   int*) data)[n+k] = ((unsigned   int*) buffer)[i];
+	}
+	else if( bpc == 16 ) ((unsigned short*) data)[n+k] = ((unsigned short*) buffer)[i];
+	else                 ((unsigned  char*) data)[n+k] = ((unsigned  char*) buffer)[i];
+      }
+      n += 3;
+    }
+
+    // Delete original memory buffer
+    if( mm ) deallocate( buffer );
+
+    // Set the new tile dimensions and data storage size
+    capacity = len;   // Need to set this manually as deallocate sets this to zero
+    dataLength = len;
+  };
+
+
+
   /// Overloaded equality operator
   friend int operator == ( const RawTile& A, const RawTile& B ) {
     if( (A.tileNum == B.tileNum) &&

src/WebPCompressor.cc

@@ -33,6 +33,7 @@ void WebPCompressor::InitCompression( const RawTile& rawtile, unsigned int strip
   tile.width = rawtile.width;
   tile.height = rawtile.height;
   tile.channels = rawtile.channels;
+  tile.bpc = rawtile.bpc;
   tile.data = rawtile.data;
   tile.dataLength = rawtile.dataLength;
   tile.memoryManaged = 0;   // We don't want the RawTile destructor to free this memory
@@ -84,24 +85,11 @@ unsigned int WebPCompressor::Finish( unsigned char* output ){
 /// Compress a single tile of data
 unsigned int WebPCompressor::Compress( RawTile& rawtile ){
 
-  // Import data from our RawTile structure
-  unsigned char* tmp = NULL;
-  const uint8_t* rgb = (uint8_t*) rawtile.data;
-
   // WebP cannot handle greyscale, so duplicate our data to 3 bands
-  if( rawtile.channels == 1 ){
-    unsigned int len = rawtile.width*rawtile.height;
-    tmp = new unsigned char[len*3];
-    unsigned int n = 0;
-    for( unsigned int i=0; i<len; i++ ){
-      tmp[n++] = rgb[i];
-      tmp[n++] = rgb[i];
-      tmp[n++] = rgb[i];
-    }
-    rgb = (uint8_t*) tmp;
-    rawtile.channels = 3;
-  }
+  if( rawtile.channels == 1 ) rawtile.triplicate();
 
+  // Import data from our RawTile structure
+  const uint8_t* rgb = (uint8_t*) rawtile.data;
 
   // Create WebP input data structure
   WebPPicture pic;
@@ -129,9 +117,7 @@ unsigned int WebPCompressor::Compress( RawTile& rawtile ){
     }
   }
 
-  // Delete any temporary buffer
-  if( tmp ) delete[] tmp;
-  
+
   // Encode our image buffer
   WebPEncode( &config, &pic );
 
@@ -173,6 +159,7 @@ unsigned int WebPCompressor::Compress( RawTile& rawtile ){
     rawtile.capacity = size;
   }
 
+
   // Copy our data back into our rawtile buffer
   memcpy( rawtile.data, buffer, size );
   rawtile.dataLength = size;