Updated README.md

README.md

@@ -1,3 +1,87 @@
 # libcaesium
 [![Build Status](https://travis-ci.org/Lymphatus/libcaesium.svg?branch=master)](https://travis-ci.org/Lymphatus/libcaesium)  
-The Caesium compression library written in C
+
+Libcaesium is a simple library performing JPEG and PNG compression/optimization using [mozjpeg](https://github.com/mozilla/mozjpeg) and [zopfli](https://github.com/google/zopfli).
+
+
+## Basic usage
+
+Libcaesium exposes one single function, auto-detecting the input file type:
+```C
+bool cs_compress(const char *input,
+                 const char *output,
+                 cs_image_pars *options);
+```
+#### Parameters
+**input** - input file path  
+**output** - output file path  
+**options** - pointer to the options struct, containing compression parameters (see below)  
+
+#### Return value
+**true** if the compression has successfully ended, or **false** if any error occurs.
+
+## Compression options
+Libcaesium supports a few compression parameters for each JPEG and PNG.
+They are defined into a top level struct containing each supported file parameters, as follows:
+```C
+typedef struct cs_image_pars
+{
+	cs_jpeg_pars jpeg;
+	cs_png_pars png;
+} cs_image_pars;
+```
+### JPEG
+```C
+typedef struct cs_jpeg_pars
+{
+	int quality;
+	bool exif_copy;
+	int dct_method;
+	/*
+	 * Parameters you have no reason to set as they will be
+	 * overwritten during the process
+	 */
+	int color_space;
+	enum TJSAMP subsample;
+	int width;
+	int height;
+} cs_jpeg_pars;
+```
+The first 3 parameters matters, in term of compression, while the others will be set by the compressor/decompressor
+during the compression progress and thus they will be overwritten.
+- **quality**: in a range from 0 to 100, the quality of the resulting image. **Note** that 0 means _optimization_ (see below). Default: 65.
+- **exif_copy**: set it to _true_ to copy EXIF tag info after compression. Default: false;
+- **dct_method**: one of the turbojpeg DCT flags. Default: TJFLAG_FASTDCT.
+
+### PNG
+```C
+typedef struct cs_png_pars
+{
+	int iterations;
+	int iterations_large;
+	int block_split_strategy;
+	bool lossy_8;
+	bool transparent;
+	int auto_filter_strategy;
+} cs_png_pars;
+```
+Those are the zopflipng compression parameters.
+- **iterations**: number of iterations (more means more compression). Default: 10.
+- **iteration_large**: number of iterations for large files. Default: 5.
+- **block_split_strategy**: filter strategy. Default: 4;
+- **lossy_8**: convert 16-bit per channel image to 8-bit per channel. Default: true.
+- **transparent**: remove colors behind alpha channel 0. Default: true.
+- **auto_filter_strategy**: legacy.
+
+# Compilation
+TODO
+
+# Installation
+TODO
+
+## Compression vs Optimization
+JPEG is a lossy format: that means you will always lose some information after each compression. So, compressing a file with
+100 quality for 10 times will result in a always different image, even though you can't really see the difference.
+Libcaesium also supports optimization, by setting the _quality_ to 0. This performs a lossy process, resulting in the same image,
+but with a smaller size (10-15% usually).  
+PNG is lossless, so libcaesium will always perform optimization rather than compression.

caesium/cstypes.h

@@ -7,9 +7,13 @@
 typedef struct cs_jpeg_pars
 {
 	int quality;
-	int color_space;
-	int dct_method;
 	bool exif_copy;
+	int dct_method;
+	/*
+	 * Parameters you have no reason to set as they will be
+	 * overwritten during the process
+	 */
+	int color_space;
 	enum TJSAMP subsample;
 	int width;
 	int height;