Issue #1937140 by ACF: Convert image_jpeg_quality() to cmi.

core/modules/image/config/image.settings.yml

 preview_image: core/modules/image/sample.png
 allow_insecure_derivatives: false
+jpeg_quality: 75

core/modules/image/image.install

@@ -176,5 +176,6 @@ function image_update_8001() {
 function image_update_8002() {
   update_variables_to_config('image.settings', array(
     'image_style_preview_image' => 'preview_image',
+    'image_jpeg_quality' => 'jpeg_quality',
   ));
 }

core/modules/system/image.gd.inc

@@ -37,7 +37,7 @@ function image_gd_settings() {
       '#description' => t('Define the image quality for JPEG manipulations. Ranges from 0 to 100. Higher values mean better image quality but bigger files.'),
       '#min' => 0,
       '#max' => 100,
-      '#default_value' => variable_get('image_jpeg_quality', 75),
+      '#default_value' => config('image.settings')->get('jpeg_quality'),
       '#field_suffix' => t('%'),
     );
 
@@ -296,7 +296,8 @@ function image_gd_save(stdClass $image, $destination) {
     return FALSE;
   }
   if ($extension == 'jpeg') {
-    $success = $function($image->resource, $destination, variable_get('image_jpeg_quality', 75));
+    $quality = config('image.settings')->get('jpeg_quality');
+    $success = $function($image->resource, $destination, $quality);
   }
   else {
     // Always save PNG images with full transparency.