Merge pull request #652 from refotografia/main

Added modes to contrast filter
brendan-duncan · May 22, 2024 · 7fa05e9 · 7fa05e9
2 parents a43a391 + dae22d0
commit 7fa05e9
Showing 1 changed file with 33 additions and 13 deletions.
diff --git a/lib/src/filter/contrast.dart b/lib/src/filter/contrast.dart
@@ -1,3 +1,4 @@
+import 'dart:math';
 import 'dart:typed_data';
 
 import '../color/channel.dart';
@@ -7,31 +8,50 @@ import '../util/math_util.dart';
 num? _lastContrast;
 late Uint8List _contrast;
 
+enum ContrastMode { proportional, scurve }
+
 /// Set the [contrast] level for the image [src].
 ///
-/// [contrast] values below 100 will decrees the contrast of the image,
-/// and values above 100 will increase the contrast. A contrast of of 100
+/// [contrast] values below 100 will decrease the contrast of the image,
+/// and values above 100 will increase the contrast. A contrast of 100
 /// will have no affect.
+
 Image contrast(Image src,
     {required num contrast,
     Image? mask,
-    Channel maskChannel = Channel.luminance}) {
+    Channel maskChannel = Channel.luminance,
+    ContrastMode mode = ContrastMode.proportional}) {
   if (contrast == 100.0) {
     return src;
   }
   if (src.hasPalette) {
     src = src.convert(numChannels: src.numChannels);
   }
-  if (contrast != _lastContrast) {
-    _lastContrast = contrast;
-
-    contrast = contrast / 100.0;
-    contrast = contrast * contrast;
-    _contrast = Uint8List(256);
-    for (var i = 0; i < 256; ++i) {
-      _contrast[i] = (((((i / 255.0) - 0.5) * contrast) + 0.5) * 255.0)
-          .clamp(0, 255)
-          .toInt();
+  if (mode == ContrastMode.proportional) {
+    if (contrast != _lastContrast) {
+      _lastContrast = contrast;
+
+      contrast = contrast / 100.0;
+      contrast = contrast * contrast;
+      _contrast = Uint8List(256);
+      for (var i = 0; i < 256; ++i) {
+        _contrast[i] = (((((i / 255.0) - 0.5) * contrast) + 0.5) * 255.0)
+            .clamp(0, 255)
+            .toInt();
+      }
+    } else {
+      if (contrast != _lastContrast) {
+        _lastContrast = contrast;
+/// 0.12 is an arbitrary adjustment to use 100 as mid point
+        contrast = (contrast / 100.0) - 0.12;
+        _contrast = Uint8List(256);
+        for (var i = 0; i < 256; ++i) {
+          _contrast[i] =
+              (((tan(((i / 128) - 1) * contrast) + 1.0) / 2.0) * 255.0)
+                  .clamp(0, 255)
+                  .toInt();
+        }
+      }
     }
   }