Use image_file_extension for picture variant rendering

app/models/alchemy/picture.rb

@@ -263,7 +263,7 @@ def deletable?
     end
 
     def image_file_extension
-      image_file&.ext&.downcase
+      read_attribute(:image_file_format)
     end
     alias_method :suffix, :image_file_extension
     deprecate suffix: :image_file_extension, deprecator: Alchemy::Deprecation

app/models/alchemy/picture_variant.rb

@@ -89,20 +89,20 @@ def encoded_image(image, options = {})
       end
 
       options = {
-        flatten: !render_format.in?(ANIMATED_IMAGE_FORMATS) && picture.image_file_format == "gif"
+        flatten: !render_format.in?(ANIMATED_IMAGE_FORMATS) && picture.image_file_extension == "gif"
       }.with_indifferent_access.merge(options)
 
       encoding_options = []
 
-      convert_format = render_format.sub("jpeg", "jpg") != picture.image_file_format.sub("jpeg", "jpg")
+      convert_format = render_format.sub("jpeg", "jpg") != picture.image_file_extension.sub("jpeg", "jpg")
 
       if encodable_image? && (convert_format || options[:quality])
         quality = options[:quality] || Alchemy.config.get(:output_image_quality)
         encoding_options << "-quality #{quality}"
       end
 
       if options[:flatten]
-        if render_format.in?(TRANSPARENT_IMAGE_FORMATS) && picture.image_file_format.in?(TRANSPARENT_IMAGE_FORMATS)
+        if render_format.in?(TRANSPARENT_IMAGE_FORMATS) && picture.image_file_extension.in?(TRANSPARENT_IMAGE_FORMATS)
           encoding_options << "-background transparent"
         end
         encoding_options << "-flatten"

spec/models/alchemy/picture_spec.rb

@@ -454,7 +454,7 @@ module Alchemy
 
     describe "#convertible?" do
       let(:picture) do
-        Picture.new(image_file_format: "image/png")
+        Picture.new(image_file_format: "png")
       end
 
       subject { picture.convertible? }
@@ -473,16 +473,16 @@ module Alchemy
         end
 
         context "and the image has a convertible format" do
-          before do
-            expect(picture).to receive(:has_convertible_format?) { true }
+          let(:picture) do
+            Picture.new(image_file_format: "png")
           end
 
           it { is_expected.to be(true) }
         end
 
         context "but the image has no convertible format" do
-          before do
-            expect(picture).to receive(:has_convertible_format?) { false }
+          let(:picture) do
+            Picture.new(image_file_format: "svg")
           end
 
           it { is_expected.to be(false) }