color model refinements

improvements to visual masking

BUILD

@@ -0,0 +1,24 @@
+cc_library(
+    name = "butteraugli_lib",
+    srcs = [
+        "butteraugli/butteraugli.cc",
+        "butteraugli/butteraugli.h",
+    ],
+    hdrs = [
+        "butteraugli/butteraugli.h",
+    ],
+    copts = ["-Wno-sign-compare"],
+    visibility = ["//visibility:public"],
+)
+
+cc_binary(
+    name = "butteraugli",
+    srcs = ["butteraugli/butteraugli_main.cc"],
+    copts = ["-Wno-sign-compare"],
+    visibility = ["//visibility:public"],
+    deps = [
+        ":butteraugli_lib",
+        "@jpeg_archive//:jpeg",
+        "@png_archive//:png",
+    ],
+)

README.md

@@ -1,27 +1,27 @@
-# Butteraugli — a tool for measuring differences between images
+# butteraugli
+
+> A tool for measuring perceived differences between images
 
 ## Introduction
 
 Butteraugli is a project that estimates the psychovisual similarity of two
-images. It gives a score for the images that is reliable in the domain of
-barely noticeable differences. Butteraugli not only gives a scalar score,
-but also a spatial map of the level of differences.
+images. It gives a score for the images that is reliable in the domain of barely
+noticeable differences. Butteraugli not only gives a scalar score, but also
+computes a spatial map of the level of differences.
 
-One of the main motivations for this project is the statistical differences
-in location and density of different color receptors, particularly the
-low density of blue cones in the fovea. Another motivation comes from
-more accurate modeling of ganglion cells, particularly the frequency
-space inhibition. 
+One of the main motivations for this project is the statistical differences in
+location and density of different color receptors, particularly the low density
+of blue cones in the fovea. Another motivation comes from more accurate modeling
+of ganglion cells, particularly the frequency space inhibition.
 
 ## Use
 
-Butteraugli can work as a quality metric for lossy image and
-video compression. On our small test corpus butteraugli performs
-better than our implementations of the reference methods, psnrhsv-m,
-ssim, and our yuv-color-space variant of ssim. One possible use is to
-define the quality level setting used in a jpeg compression, or to
-compare two or more compression methods at the same level of psychovisual
-differences.
+Butteraugli can work as a quality metric for lossy image and video compression.
+On our small test corpus butteraugli performs better than our implementations of
+the reference methods, psnrhsv-m, ssim, and our yuv-color-space variant of ssim.
+One possible use is to define the quality level setting used in a jpeg
+compressor, or to compare two or more compression methods at the same level of
+psychovisual differences.
 
 Butteraugli is intended to be a research tool more than a practical tool for
 choosing compression formats. We don't know how well butteraugli performs with
@@ -30,7 +30,39 @@ roughly corresponding to jpeg qualities 90 to 95.
 
 ## Interface
 
-Only a C++ interface is provided. The interface takes two images, gives out a
-map and a scalar value defining the difference. The scalar value can be
-compared to two reference values that divide the value space into three
-experience classes: 'great', 'acceptable' and 'not acceptable'. 
+Only a C++ interface is provided. The interface takes two images and outputs a
+map together with a scalar value defining the difference. The scalar value can
+be compared to two reference values that divide the value space into three
+experience classes: 'great', 'acceptable' and 'not acceptable'.
+
+## Build instructions
+
+Install [Bazel](http://bazel.io) by following the
+[instructions](https://www.bazel.io/docs/install.html). Run `bazel build -c opt
+//:butteraugli` in the directory that contains this README file to build the
+[command-line utility](#cmdline-tool). If you want to use Butteraugli as a
+library, depend on the `//:butteraugli_lib` target.
+
+Alternatively, you can use the Makefile provided in the `butteraugli` directory,
+after ensuring that [libpng](http://www.libpng.org/) and
+[libjpeg](http://ijg.org/) are installed. On some systems you might need to also
+install corresponding `-dev` packages.
+
+The code is portable and also compiles on Windows after defining
+`_CRT_SECURE_NO_WARNINGS` in the project settings.
+
+## Command-line utility {#cmdline-tool}
+
+Butteraugli, apart from the library, comes bundled with a comparison tool. The
+comparison tool supports PNG and JPG images as inputs. To compare images, run:
+
+```
+butteraugli image1.{png|jpg} image2.{png|jpg}
+```
+
+The tool can also produce a heatmap of differences between images. The heatmap
+will be output as a PNM image. To produce one, run:
+
+```
+butteraugli image1.{png|jpg} image2.{png|jpg} heatmap.pnm
+```

WORKSPACE

@@ -0,0 +1,25 @@
+workspace(name = "butteraugli")
+
+new_http_archive(
+  name = "png_archive",
+  url = "http://github.com/glennrp/libpng/archive/v1.2.53.zip",
+  sha256 = "c35bcc6387495ee6e757507a68ba036d38ad05b415c2553b3debe2a57647a692",
+  strip_prefix = "libpng-1.2.53",
+  build_file = "png.BUILD",
+)
+
+new_http_archive(
+  name = "zlib_archive",
+  url = "http://zlib.net/zlib-1.2.8.tar.gz",
+  sha256 = "36658cb768a54c1d4dec43c3116c27ed893e88b02ecfcb44f2166f9c0b7f2a0d",
+  strip_prefix = "zlib-1.2.8",
+  build_file = "zlib.BUILD",
+)
+
+new_http_archive(
+  name = "jpeg_archive",
+  url = "http://www.ijg.org/files/jpegsrc.v9a.tar.gz",
+  sha256 = "3a753ea48d917945dd54a2d97de388aa06ca2eb1066cbfdc6652036349fe05a7",
+  strip_prefix = "jpeg-9a",
+  build_file = "jpeg.BUILD",
+)

butteraugli/Makefile

@@ -0,0 +1,7 @@
+LDLIBS += -lpng -ljpeg
+CXXFLAGS += -std=c++11 -I..
+LINK.o = $(LINK.cc)
+
+all: butteraugli.o butteraugli_main.o butteraugli
+
+butteraugli: butteraugli.o butteraugli_main.o