Clean-up solarize code

Author: brendan-duncan

doc/filters.md

@@ -328,6 +328,15 @@ Image sobel(Image src, { num amount = 1, Image? mask, Channel maskChannel = Chan
 
 ![sobel](images/filter/sobel.png)
 
+### [solarize](https://pub.dev/documentation/image/latest/image/solarize.html)
+
+```dart
+enum SolarizeMode { highlights, shadows }
+Image solarize(Image src, { required int threshold, SolarizeMode mode = SolarizeMode.highlights })
+```
+
+![solarize](images/filter/solarize_highlights.png)
+
 ### [stretchDistortion](https://pub.dev/documentation/image/latest/image/stretchDistortion.html)
 
 ```dart

doc/images/filter/solarize_highlights.png

@@ -77,6 +77,7 @@ export 'src/filter/sepia.dart';
 export 'src/filter/sketch.dart';
 export 'src/filter/smooth.dart';
 export 'src/filter/sobel.dart';
+export 'src/filter/solarize.dart';
 export 'src/filter/stretch_distortion.dart';
 export 'src/filter/vignette.dart';
 export 'src/font/arial_14.dart';

doc/images/filter/solarize_shadows.png

@@ -1,25 +1,23 @@
 import '../image/image.dart';
 import '../util/min_max.dart';
 
-  enum Modes {
-    highlights,
-    shadows
-  }
-/// Solarize the colors of the [src] image - Started from invert.dart file.
-Image solarize(Image src, {required int threshold, required int md}) {
-  /// threshold should be int from 1 to 254; mode should either '0' or '1'
-  /// mode '0' is normal solarization, bright objetcs become black
-  /// mode '1' will solarize the shadows like a Man Ray photograph
+enum SolarizeMode { highlights, shadows }
+
+/// Solarize the colors of the [src] image.
+/// {threshold} should be int from 1 to 254. If {mode} is
+/// SolarizeMode.highlights, bright objects become black, otherwise it will
+/// solarize shadows.
+Image solarize(Image src,
+    {required int threshold, SolarizeMode mode = SolarizeMode.highlights}) {
   final max = src.maxChannelValue;
-  final trld = (max * (threshold / 255)).toInt();
-  final mode = Modes.values[md].toString();
+  final thresholdRange = (max * (threshold / 255)).toInt();
   for (final frame in src.frames) {
     if (src.hasPalette) {
       final p = frame.palette!;
       final numColors = p.numColors;
       for (var i = 0; i < numColors; ++i) {
-        if (mode == "highlights") {
-          if (p.getGreen(i) > trld) {
+        if (mode == SolarizeMode.highlights) {
+          if (p.getGreen(i) > thresholdRange) {
             final r = max - p.getRed(i);
             final g = max - p.getGreen(i);
             final b = max - p.getBlue(i);
@@ -31,7 +29,7 @@ Image solarize(Image src, {required int threshold, required int md}) {
             p.setRgb(i, r, g, b);
           }
         } else {
-          if (p.getGreen(i) < trld) {
+          if (p.getGreen(i) < thresholdRange) {
             final r = max - p.getRed(i);
             final g = max - p.getGreen(i);
             final b = max - p.getBlue(i);
@@ -47,8 +45,8 @@ Image solarize(Image src, {required int threshold, required int md}) {
     } else {
       if (max != 0.0) {
         for (final p in frame) {
-          if (mode == "highlights") {
-            if (p.g > trld) {
+          if (mode == SolarizeMode.highlights) {
+            if (p.g > thresholdRange) {
               p
                 ..r = max - p.r
                 ..g = max - p.g
@@ -60,7 +58,7 @@ Image solarize(Image src, {required int threshold, required int md}) {
                 ..b = p.b;
             }
           } else {
-            if (p.g < trld) {
+            if (p.g < thresholdRange) {
               p
                 ..r = max - p.r
                 ..g = max - p.g
@@ -77,8 +75,7 @@ Image solarize(Image src, {required int threshold, required int md}) {
     }
   }
 
-  /// I used code from normalize here with the original
-  /// max value and zero to improve contrast
+  /// max value and zero are used to improve contrast
   const num a = 0;
   final num b = max;
 
@@ -94,7 +91,7 @@ Image solarize(Image src, {required int threshold, required int md}) {
   final fM = mx.toDouble();
 
   if (mn != a || mx != b) {
-    for (var frame in src.frames) {
+    for (final frame in src.frames) {
       for (final p in frame) {
         p
           ..r = (p.r - fm) / (fM - fm) * (b - a) + a

lib/image.dart

@@ -0,0 +1,27 @@
+import 'dart:io';
+import 'package:image/image.dart';
+import 'package:test/test.dart';
+
+import '../_test_util.dart';
+
+void main() {
+  group('Filter', () {
+    test('solarize highlights', () {
+      final bytes = File('test/_data/png/buck_24.png').readAsBytesSync();
+      final i0 = decodePng(bytes)!;
+      solarize(i0, threshold: 100);
+      File('$testOutputPath/filter/solarize_highlights.png')
+        ..createSync(recursive: true)
+        ..writeAsBytesSync(encodePng(i0));
+    });
+
+    test('solarize shadows', () {
+      final bytes = File('test/_data/png/buck_24.png').readAsBytesSync();
+      final i0 = decodePng(bytes)!;
+      solarize(i0, threshold: 100, mode: SolarizeMode.shadows);
+      File('$testOutputPath/filter/solarize_shadows.png')
+        ..createSync(recursive: true)
+        ..writeAsBytesSync(encodePng(i0));
+    });
+  });
+}