Added ability to specify lossless WebP compression by specifying a qu…

…ality factor of -1

ChangeLog

@@ -1,3 +1,7 @@
+16/01/2024:
+	- Added ability to specify lossless WebP compression by specifying a quality factor of -1
+
+
 15/01/2024:
 	- Fix to IIIF size calculation for region requests that go beyond the boundaries of the image
 

src/Environment.h

@@ -148,8 +148,8 @@ class Environment {
     int quality;
     if( envpara ){
       quality = atoi( envpara );
-      if( quality > 100 ) quality = 900;
-      if( quality < 0 ) quality = 0;
+      if( quality > 100 ) quality = 100;
+      if( quality < -1 ) quality = -1;  // Allow -1 = lossless
     }
     else quality = WEBP_QUALITY;
 

src/Main.cc

@@ -385,7 +385,9 @@ int main( int argc, char *argv[] )
     logfile << "Setting default PNG compression level to " << png_quality << endl;
 #endif
 #ifdef HAVE_WEBP
-    logfile << "Setting default WebP compression level to " << webp_quality << endl;
+    logfile << "Setting default WebP compression level to ";
+    if( webp_quality == -1 ) logfile << "lossless" << endl;
+    else logfile << webp_quality << endl;
 #endif
     logfile << "Setting maximum CVT size to " << max_CVT << endl;
     logfile << "Setting HTTP Cache-Control header to '" << cache_control << "'" << endl;

src/WebPCompressor.h

@@ -1,7 +1,7 @@
 /*  WebP Compressor Class:
     Handles alpha channels, ICC profiles and XMP metadata
 
-    Copyright (C) 2022-2023 Ruven Pillay
+    Copyright (C) 2022-2024 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
@@ -65,7 +65,15 @@ class WebPCompressor : public Compressor {
     WebPConfigInit( &config );
     config.method = 0;         // Fastest encoding
     config.thread_level = 1;   // Enable threading
-    config.quality = this->Q;  // WebP's quality range is 0-100
+
+    // Update our WebP config structure depending on whether lossless or lossy compression requested
+    if( compressionLevel == -1 ){
+      // -1 indicates lossless
+      config.lossless = 1;
+      config.quality = 0;      // Zero means fastest for lossless
+    }
+    // WebP's lossy quality range is 0-100
+    else config.quality = this->Q;
 
     // Create our muxer object
     mux = WebPMuxNew();
@@ -138,12 +146,18 @@ class WebPCompressor : public Compressor {
     // WebP quality ranges from 0 (best compression - smallest size) to 100 (worst compression - largest size)
     this->Q = quality;
 
-    // WebP compression level
-    if( Q < 0 ) Q = 0;
+    // Limit to WebP quality range - negative values indicate lossless
+    if( this->Q < 1 ) Q = -1;
     else if( Q > 100 ) Q = 100;
 
-    // Update our WebP config structure
-    config.quality = Q;
+    // Update our WebP config structure depending on whether lossless or lossy compression requested
+    if( this->Q == -1 ){
+      // -1 indicates lossless
+      config.lossless = 1;
+      config.quality = 0;      // Zero means fastest for lossless
+    }
+    // WebP's lossy quality range is 0-100
+    else config.quality = this->Q;
   }