Set admin picture thumbnail quality to 90

Make the picture thumbnail quality independent from the
frontend output_image_quality config.

Using 90 as value for quality should be a good compromise
between file size and image quality.

The same image with quality of 100 is three times the size of an image with quality of 90 while having nearly the same image
quality for a small thumbnail. An large thumbnail (as used in the
image cropper) is ten times the size in 100% quality!

app/models/alchemy/picture.rb

@@ -22,6 +22,8 @@
 
 module Alchemy
   class Picture < BaseRecord
+    THUMBNAIL_QUALITY = 90
+
     THUMBNAIL_SIZES = {
       small: "80x60",
       medium: "160x120",
@@ -195,14 +197,16 @@ def url(options = {})
     # Returns an url for the thumbnail representation of the picture
     #
     # @param [String] size - The size of the thumbnail
+    # @param [Integer] quality - The quality of the thumbnail
     #
     # @return [String]
-    def thumbnail_url(size: "160x120")
+    def thumbnail_url(size: "160x120", quality: THUMBNAIL_QUALITY)
       return if image_file.nil?
 
       url(
         flatten: true,
         format: "webp",
+        quality: quality,
         size: size
       )
     end

app/models/concerns/alchemy/picture_thumbnails.rb

@@ -84,7 +84,8 @@ def thumbnail_url_options
         crop_from: crop && crop_from.presence || default_crop_from&.join("x"),
         crop_size: crop && crop_size.presence || default_crop_size&.join("x"),
         flatten: true,
-        format: "webp"
+        format: "webp",
+        quality: Alchemy::Picture::THUMBNAIL_QUALITY
       }
     end
 

lib/alchemy/test_support/having_picture_thumbnails_examples.rb

@@ -382,6 +382,7 @@
           crop_size: nil,
           flatten: true,
           format: "webp",
+          quality: Alchemy::Picture::THUMBNAIL_QUALITY,
           size: "160x120"
         )
       end
@@ -401,6 +402,7 @@
             crop_size: nil,
             flatten: true,
             format: "webp",
+            quality: Alchemy::Picture::THUMBNAIL_QUALITY,
             size: "160x120"
           )
         end

spec/models/alchemy/picture_spec.rb

@@ -335,6 +335,7 @@ module Alchemy
           expect(picture).to receive(:url).with(
             flatten: true,
             format: "webp",
+            quality: Alchemy::Picture::THUMBNAIL_QUALITY,
             size: "160x120"
           )
           thumbnail_url
@@ -347,11 +348,26 @@ module Alchemy
             expect(picture).to receive(:url).with(
               flatten: true,
               format: "webp",
+              quality: Alchemy::Picture::THUMBNAIL_QUALITY,
               size: "800x600"
             )
             thumbnail_url
           end
         end
+
+        context "with quality given" do
+          subject(:thumbnail_url) { picture.thumbnail_url(quality: 50) }
+
+          it "returns the url to the thumbnail" do
+            expect(picture).to receive(:url).with(
+              flatten: true,
+              format: "webp",
+              quality: 50,
+              size: "160x120"
+            )
+            thumbnail_url
+          end
+        end
       end
     end