How To Optimize Png Images

My previous post introduces unopen to tools to optimize JPEG images. The focus of this postal service is on optimizing PNG images. Two gratis tools volition live on presented: optipng, together with pngquant. The former, lossless, together with the latter, lossy.

optipng

optipng optimizes a PNG file past times compressing it losslessly.

The ascendance to install optipng on Debian/Ubuntu is:

 $ sudo apt-get install optipng 

For Fedora/Centos/RedHat, execute:

 $ sudo yum install optipng 

To optimize a PNG file named input.png:

 $ optipng -o7 -strip all -out out.png -clobber input.png 

Notes:

• Output PNG file.

  By default, optipng compresses the PNG file in-place, thus overwriting the master copy file. To write the output to a dissimilar file, role the -out choice to specify a novel output file. If the specified output file already exists, the -clobber choice allows it to live on overwritten. The -clobber is useful if y'all are running the ascendance to a greater extent than than once.

  Alternatively, supersede -out out.png amongst the -backup option. As a result, optipng commencement backs upward the master copy input file earlier compressing the input file in-place.

• Meta data.

  The -strip all choice removes all meta information from the image.

• Optimization level.

  The -o choice specifies the optimization level, which ranges from 0 to 7. Level seven offers the highest compression, only also takes the longest fourth dimension to complete. It has been reported that in that location is a marginal supply of improved compression equally y'all growth the optimization level. The results obtained from my ain 1-image evidence confirm that. The tests demo that the default optimization score of ii is pretty good, together with that higher levels create non offering a big growth inward compression.

  Optimization level	Compression fourth dimension (Seconds)	File Size (Bytes)	% Reduction
  Original	N/A	285,420	N/A
  0	0.03	285,012	0.14
  1	3.07	242,548	15.02
  ii	5.77	242,548	15.02
  three	10.33	242,175	15.15
  four	17.54	241,645	15.34
  five	34.61	241,258	15.47
  half dozen	35.86	241,645	15.34
  seven	71.37	241,258	15.47

pngquant

pngquant uses lossy compression techniques to cut down the size of a PNG image. It converts a 32-bit PNG icon to a 8-bit paletted image. More specifically, instead of storing each pixel equally a 4-channel, 32-bit RGBA value, each pixel is stored equally an 8-bit reference for mapping to a color inward a palette. This 8-bit color palette is embedded inward the image, together with is capable of defining 256 unique colors. The fox together with then becomes how to cut down the full position out of colors inward an icon without sacrificing likewise much perceivable quality.

To install pngquant on Debian/Ubuntu:

 $ sudo apt-get install pngquant 

Note that the pngquant version shipped on Debian Wheezy is obsolete (1.0), together with non recommended past times the official pngquant spider web site. The examples below were run on version 2.0.0.

To install pngquant on Fedora/Centos/Redhat:

 $ sudo yum install pngquant 

To optimize a PNG image:

 $ pngquant -o output.png --force --quality=70-80 input.png 

Notes:

• Specify the output icon file advert using the -o option. Without it, the default output advert is the same equally the input except that the extension is changed (for example, input-fs8.png).
• Without the --force option, pngquant volition non overwrite the output file if it already exists.
• Since the introduction of the --quality=min-max choice inward version 1.8, the position out of colors is automatically derived based on the specified instant together with max lineament values. The instant together with max values arrive at from 0 to 100, 100 existence the highest quality.

  pngquant uses solely the to the lowest degree position out of colors required to watch or overstep the max lineament score (80 inward the inward a higher house example). If it cannot accomplish fifty-fifty the instant lineament value (70), the output icon is non saved.

Below summarizes the results of optimizing i randomly chosen PNG image. It is non intended to live on scientific or conclusive. Rather, I promise to hand y'all an sentiment of the scale of reduction that is possible.

Quality min-max	Orig	70-90%	70-80%
File Size (Bytes)	1,281,420	445,464	376,221
% Reduction	-	65.2	70.6

The ii programs - optipng together with pngquant - are non mutually exclusive. You volition larn the close compression from running pngquant. But if y'all desire to larn the final possible 1% or so compression, y'all may commencement run pngquant, together with then optipng.

 $ pngquant -o lossy.png --force --quality=70-80 input.png $ optipng -o7 -strip all -out output.png lossy.png 

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