Add a way to configure threshold

config/responsive-images.php

@@ -36,7 +36,7 @@
     |
     */
     'force_absolute_urls' => false,
-    
+
     /*
     |--------------------------------------------------------------------------
     | Queue
@@ -61,6 +61,20 @@
 
     'max_width' => null,
 
+    /*
+    |--------------------------------------------------------------------------
+    | Dimension Calculator Threshold
+    |--------------------------------------------------------------------------
+    |
+    | Define the file size threshold at which the default
+    | dimension calculator decides to generate a new
+    | variant. By default, this is 30% smaller.
+    | Must be a value: 0 < x < 1
+    |
+    */
+
+    'dimension_calculator_threshold' => 0.7,
+
     /*
     |--------------------------------------------------------------------------
     | Placeholder

src/ResponsiveDimensionCalculator.php

@@ -77,7 +77,7 @@ protected function calculateDimensions(int $assetFilesize, int $assetWidth, int
         $pixelPrice = $predictedFileSize / $area;
 
         while (true) {
-            $predictedFileSize *= 0.7;
+            $predictedFileSize *= config('statamic.responsive-images.dimension_calculator_threshold', 0.7);
 
             $newWidth = (int) floor(sqrt(($predictedFileSize / $pixelPrice) / $ratioForFilesize));
 

tests/Feature/DimensionCalculatorTest.php

@@ -130,6 +130,23 @@ function getWidths(Asset $asset, Breakpoint $breakpoint): array
     ]);
 });
 
+it('can calculate the optimized widths for different dimensions with a custom threshold', function () {
+    config()->set('statamic.responsive-images.dimension_calculator_threshold', 0.25);
+
+    $stubbedAsset = stubAsset(2400, 1800, 3000 * 1024);
+    $breakpoint = new Breakpoint($stubbedAsset, 'default', 0, []);
+
+    $widths = getWidths($stubbedAsset, $breakpoint);
+
+    expect($widths)->toEqual([
+        0 => 2400,
+        1 => 1200,
+        2 => 600,
+        3 => 300,
+        4 => 150,
+    ]);
+});
+
 it('filters out widths to be less than max width specified in config', function() {
     config()->set('statamic.responsive-images.max_width', 300);
 
@@ -205,4 +222,4 @@ function getWidths(Asset $asset, Breakpoint $breakpoint): array
     $calculatedDimensions = app(DimensionCalculator::class)->calculateForImgTag($breakpoint);
 
     expect($calculatedDimensions->getHeight())->toEqual(170);
-});
+});