pieroxy.netcompression

JPEG Compression: Is 80 the magic quality - Part 1 - the retina screens

Sun, 01 May 2016 07:45:00 GMT

Foreword - encoding JPEGs

How do you encode your JPEGs ?

Let's take a concrete example. You you have a 150x150 image. You want to compress it in JPG, but which quality settings should you use? JPEG encoders usually take a quality setting as a parameter, between Q1 and Q100, where 1 is the worst quality and 100 the best.

An image encoded in different qualities. The legend shows the quality setting and the corresponding filesize.

Q 10 - 1579B

Q 20 - 1960B

Q 30 - 2260B

Q 40 - 2513B

Q 50 - 2729B

Q 60 - 2973B

Q 70 - 3308B

Q 80 - 3826B

Q 90 - 4939B

Q 100 - 32KB

We can see that the greater the quality, the better and bigger the image. There is clearly a compromise to be done as Q100 is clearly too big an image and the increase in filesize doesn't translate to an equivalent increase in visual quality. 80 seems a sensible choice. The filesize is 3.8KB.

While this 80 quality settings is the most sensible, we're going to show that in some circumstances it is completely off the mark.

In this first part, we'll focus on high density displays, aka retina screens as they were first introduced by Apple a few years ago.

lz-string: We'll try to make it faster

Tue, 21 May 2013 08:19:00 GMT

I've setup a small page where I share my findings in trying to optimize the implementation of lz-string. This work will continue in the coming weeks. You can leave a comment in this blog entry for any feedback.

Just released: lz-string

Thu, 09 May 2013 09:27:00 GMT

lz-string is a compression program for JavaScript in the browser, based on LZW. It is fast, meant for localStorage or any other string-based storage in JavaScript, and is particularly efficient on short strings.

All can be read on the home page: https://pieroxy.net/blog/pages/lz-string/index.html And a demo can be found below for live compression: https://pieroxy.net/blog/pages/lz-string/demo.html