--- a/lib/sparklines.rb	2023-04-26 07:46:30.263829168 +0200
+++ b/lib/sparklines.rb	2023-04-26 07:48:47.140656193 +0200
@@ -685,7 +685,7 @@
     @draw = Magick::Draw.new
     @draw.pointsize = @@pointsize # TODO Use height
     @draw.pointsize = @options[:font_size] if @options.has_key?(:font_size)
-    @canvas = Magick::Image.new(w , h) { self.background_color = bkg_col }
+    @canvas = Magick::Image.new(w , h) { |image| image.background_color = bkg_col }
 
     # Make room for label and last value
     unless @options[:label].nil?
@@ -697,7 +697,7 @@
       w += @label_and_data_last_width
     end
 
-    @canvas = Magick::Image.new(w , h) { self.background_color = bkg_col }
+    @canvas = Magick::Image.new(w , h) { |image| image.background_color = bkg_col }
     @canvas.format = "PNG"
 
     # Draw label and last value