From 766e67ce575aaa6f817c842d591948c7c02b84cc Mon Sep 17 00:00:00 2001
From: Sam <sam.saffron@gmail.com>
Date: Wed, 2 Jan 2019 17:19:52 +1100
Subject: [PATCH] FEATURE: introduce lossy color optimization on resized pngs

This feature ensures optimized images run via pngquant, this results extreme amounts of savings for resized images. Effectively the only impact is that the color palette on small resized images is reduced to 256.

To ensure safety we only apply this optimisation to images smaller than 500k.

This commit also makes a bunch of image specs less fragile.
---
 app/models/optimized_image.rb       |   6 +++++-
 lib/file_helper.rb                  |   9 +++++++--
 spec/fixtures/images/pngquant.png   | Bin 0 -> 9558 bytes
 spec/lib/upload_creator_spec.rb     |  21 +++++++++++++++++++++
 spec/models/optimized_image_spec.rb |  23 ++++++++++++-----------
 5 files changed, 45 insertions(+), 14 deletions(-)
 create mode 100644 spec/fixtures/images/pngquant.png

diff --git a/app/models/optimized_image.rb b/app/models/optimized_image.rb
index 01f870baa6b..5e5e8e41919 100644
--- a/app/models/optimized_image.rb
+++ b/app/models/optimized_image.rb
@@ -318,9 +318,13 @@ class OptimizedImage < ActiveRecord::Base
     convert_with(instructions, to, opts)
   end
 
+  MAX_PNGQUANT_SIZE = 500_000
+
   def self.convert_with(instructions, to, opts = {})
     Discourse::Utils.execute_command(*instructions)
-    FileHelper.optimize_image!(to)
+
+    allow_pngquant = to.downcase.ends_with?(".png") && File.size(to) < MAX_PNGQUANT_SIZE
+    FileHelper.optimize_image!(to, allow_pngquant: allow_pngquant)
     true
   rescue => e
     if opts[:raise_on_error]
diff --git a/lib/file_helper.rb b/lib/file_helper.rb
index f146b8b139d..3f148fc278c 100644
--- a/lib/file_helper.rb
+++ b/lib/file_helper.rb
@@ -82,7 +82,12 @@ class FileHelper
     tmp
   end
 
-  def self.optimize_image!(filename)
+  def self.optimize_image!(filename, allow_pngquant: false)
+    pngquant_options = false
+    if allow_pngquant
+      pngquant_options = { allow_lossy: true }
+    end
+
     ImageOptim.new(
       # GLOBAL
       timeout: 15,
@@ -92,7 +97,7 @@ class FileHelper
       advpng: false,
       pngcrush: false,
       pngout: false,
-      pngquant: false,
+      pngquant: pngquant_options,
       # JPG
       jpegoptim: { strip: SiteSetting.strip_image_metadata ? "all" : "none" },
       jpegtran: false,
diff --git a/spec/fixtures/images/pngquant.png b/spec/fixtures/images/pngquant.png
new file mode 100644
index 0000000000000000000000000000000000000000..2ffb274f20acd27e4e90a621370c709e50b09dbb
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diff --git a/spec/lib/upload_creator_spec.rb b/spec/lib/upload_creator_spec.rb
index 04ac72f00b1..897c946aeea 100644
--- a/spec/lib/upload_creator_spec.rb
+++ b/spec/lib/upload_creator_spec.rb
@@ -98,6 +98,27 @@ RSpec.describe UploadCreator do
       end
     end
 
+    describe 'pngquant' do
+      let(:filename) { "pngquant.png" }
+      let(:file) { file_from_fixtures(filename) }
+
+      it 'should apply pngquant to optimized images' do
+        upload = UploadCreator.new(file, filename,
+          pasted: true,
+          force_optimize: true
+        ).create_for(user.id)
+
+        # no optimisation possible without losing details
+        expect(upload.filesize).to eq(9558)
+
+        thumbnail_size = upload.get_optimized_image(upload.width, upload.height, {}).filesize
+
+        # pngquant will lose some colors causing some extra size reduction
+        expect(thumbnail_size).to be < 7500
+      end
+
+    end
+
     describe 'converting to jpeg' do
       let(:filename) { "should_be_jpeg.png" }
       let(:file) { file_from_fixtures(filename) }
diff --git a/spec/models/optimized_image_spec.rb b/spec/models/optimized_image_spec.rb
index 45c96abbcd2..9aaa86442c8 100644
--- a/spec/models/optimized_image_spec.rb
+++ b/spec/models/optimized_image_spec.rb
@@ -6,7 +6,7 @@ describe OptimizedImage do
 
   unless ENV["TRAVIS"]
     describe '.crop' do
-      it 'should work correctly (requires correct version of image optim)' do
+      it 'should produce cropped images' do
         tmp_path = "/tmp/cropped.png"
 
         begin
@@ -17,12 +17,15 @@ describe OptimizedImage do
             5
           )
 
-          fixture_path = "#{Rails.root}/spec/fixtures/images/cropped.png"
-          fixture_hex = Digest::MD5.hexdigest(File.read(fixture_path))
+          # we don't want to deal with something new here every time image magick
+          # is upgraded or pngquant is upgraded, lets just test the basics ...
+          # cropped image should be less than 120 bytes
 
-          cropped_hex = Digest::MD5.hexdigest(File.read(tmp_path))
+          cropped_size = File.size(tmp_path)
+
+          expect(cropped_size).to be < 120
+          expect(cropped_size).to be > 50
 
-          expect(cropped_hex).to eq(fixture_hex)
         ensure
           File.delete(tmp_path) if File.exists?(tmp_path)
         end
@@ -128,7 +131,7 @@ describe OptimizedImage do
     end
 
     describe '.downsize' do
-      it 'should work correctly (requires correct version of image optim)' do
+      it 'should downsize logo' do
         tmp_path = "/tmp/downsized.png"
 
         begin
@@ -138,12 +141,10 @@ describe OptimizedImage do
             "100x100\>"
           )
 
-          fixture_path = "#{Rails.root}/spec/fixtures/images/downsized.png"
-          fixture_hex = Digest::MD5.hexdigest(File.read(fixture_path))
+          info = FastImage.new(tmp_path)
+          expect(info.size).to eq([100, 27])
+          expect(File.size(tmp_path)).to be < 2300
 
-          downsized_hex = Digest::MD5.hexdigest(File.read(tmp_path))
-
-          expect(downsized_hex).to eq(fixture_hex)
         ensure
           File.delete(tmp_path) if File.exists?(tmp_path)
         end