SVGCompress 0.19

Compress svg graphics

Highlights

SVGcompress is a pure python module for simplifying/compressing svg (Scalable Vector Graphics) files. Have you ever tried to output a plot in vector format (pdf, svg, eps, etc.) and been surprised that your file weighs 10 or 20MB? Needed to submit a vector figure for publication but ran up against the file size limit? Before you try to get away with the old standby of embedding a raster image in your vector and hoping the journal doesn’t notice, try SVGCompress! SVGCompress can help pare down your file size by:

• Removing tiny polygons - Reduce the number of polygons in your image by removing those below a small threshold size. The size threshold can be based on polygon area or circumference.

• Simplifying shapes - Reduce the complexity of your polygons using the Ramer–Douglas–Peucker algorithm.

• Merging adjacent or overlapping shapes - Merging can be accomplished by taking the union of overlapping polygons or through the construction of a minimum convex hull.

Installation

SVGCompress has only been tested in Python 2.7

Installation should be through pip:

$ pip install SVGCompress

Requires the following non-standard libraries:

• Numpy

• svg.path

• Shapely

• rdp

Important

SVGCompress depends upon Shapely, which requires the GEOS framework (http://trac.osgeo.org/geos). If you operate on Windows, pip will install the required files along with Shapely, but this will NOT happen with other operating systems. For non-Windows users, the most convenient way of installing the GEOS framework is through a program such as Canopy (free with academic license) or similar IDLE with an included package manager.

Usage Notes

Usage of SVGCompress is through the class Compress, or through the convenience function compress_by_method. The function svg_compress.test() contains usage examples demonstrating all of the compression methods with compress_by_method.

compress_by_method API:

Convenience function for 1-step compression of svg files.

Inputs:

filename (str) - Path to svg file to compress, e.g. ‘test_vector.svg’

compression_type (str) - how to carry out the compression. Options are ‘delete’ (remove polygons by size), ‘simplify’ (simplify polygons), and ‘merge’ (merge neighboring or overlapping polygons).

curve_fidelity (int) - All polygons affected by compression (e.g. those that are simplified) need to first be linearized so as to convert smooth curves into a set of discrete coordinates. curve_fidelity sets the number of coordinates to use to interpolate a curve. The larger the number, the more computation the code will need to perform. Optional, defaults to 10.

outputfile (str) - Path to output svg. Optional, defaults to ‘originalname_compressed.svg’

pre_select (bool) - If True, will perform the compression only on a subset of the polygons in the svg that are below a certain size threshold. Optional, defaults to False.

selection_tuple (tuple) - If pre_select == True, the selection tuple (‘criteria’, threshold) determines the criteria for selection (‘bboxarea’ for the area of the bounding box of a polygon, or ‘circumference’ for its circumference) and the threshold size. Optional, defaults to (‘’, ‘’)

kwargs - Depending on the compression type and the pre-selection criteria, additional key word arguments may be required. See compress_by_merging, compress_by_deletion, and compress_by_simplification in class Compress for the valid keyword arguments when compression_type = ‘merge’, ‘delete’, and ‘simplify’ respectively.

Outputs:

Compressed svg in the directory given by outputfile or in the code directory with the name ‘originalname_compressed.svg’.

A report string outputted to the console will also state some general indicators about the success of the compression, the path of the outputted svg, and the initial and compressed file sizes.

Producing/converting svg graphics

Producing your figures in svg format can be done through Matplotlib. This is especially convenient if you have a graphics editor such as Inkscape (free) which will allow you to do things such as modify the font and color of text or lines directly in the svg, without having to re-run your code. You can also use this to convert one of your svg files into an alternate vector format such as pdf or eps.

Examples

The directory SVGCompress/test contains examples of each compression algorithm on three different files: One is a demonstration graphic (test_vector.svg) and the second and third are actual vector plots (map_test.svg, matplotlib_test.svg)

For example, running the following call to SVGCompress.compress_by_method:

compress_by_method(filename = 'test_vector.svg', compression_type = 'merge',
                                  curve_fidelity = 10, pre_select = True, selection_tuple = ('bboxarea', 300),
                                  epsilon = 5, bufferDistance = 5, operation_key = 'hull')

compresses the test_vector.svg demonstration file from 87 to 30 KB by constructing convex hulls (operation_key = ‘hull’) around small neighboring polygons (bounding box area < 1000 pixels) to lessen the total number of polygons and then using the Ramer–Douglas–Peucker algorithm to simplify them.

The ‘test_vector series’ in the folder ‘test’ contains examples of other compression routines. Note that these examples were designed to make the changes that occur during compression obvious. For a more subtle example of compression, see the map_test series.

Version

0.19 - Not extensively tested. Please email me to let me know of any issues.

Changelog

0.19 (JULY/22/2014)

• Changed compress_by_merging default behavior to group_by_color = True

• Appended README with critical information on Shapely installation

0.18 (JULY/22/2014)

• Fixed issue with clipping paths - Code previously threw an exception when trying to extract coordinate data from clipping paths

• Updated README with a usage example

• Fixed bug in install_requires that crashed installation with pip