PNG images are compressed and slow

Web Performance Discuss Test Results
1

http://www.webpagetest.org/result/121127_JQ_301/1/details/

Item 21 to 28. Most of them are repeated images.

I don’t know why test shown that there are compressed. The loading time for those images also slow compare to their size…

<IfModule mod_mime.c> AddType application/x-javascript .js AddType text/css .css </IfModule> <IfModule mod_deflate.c> AddOutputFilterByType DEFLATE text/css application/x-javascript text/x-component text/html text/richtext image/svg+xml text/plain text/xsd text/xsl text/xml image/x-icon application/javascript <IfModule mod_setenvif.c> BrowserMatch ^Mozilla/4 gzip-only-text/html BrowserMatch ^Mozilla/4\.0[678] no-gzip BrowserMatch \bMSIE !no-gzip !gzip-only-text/html </IfModule> <IfModule mod_headers.c> Header append Vary User-Agent env=!dont-vary </IfModule> </IfModule>

2

Based on the response headers the images aren’t being gzipped see WebPageTest Test - WebPageTest Details for example.

How are the images stored?

TTFB i.e. time between request being made and the start of response received is slow, which suggests either the request takes a long time to get there or the server is slow generating the response.

If you look at request 22 for example 2757ms to receive a response but only 1ms to download it (it probably fits in a single TCP packet)

Most of the images are pretty small, have you thought about using datauris or a sprite image?

3

I looked at Full Optimization Checklist and there are 82% compresss img and from 18 to last img are checked. Thus I thought there were compressed…

Those img are repeated img and I excluded them from sprites. At least I tried included them and applied to website but I can see other imgs in the sprite.

I did informed my host regarding TTFB and webpagetest but they told me it mostly test scripts or something like that… I asked them to reduced it without increasing the resources.

4

Image compression looks at JPEG images and looks for an opportunity to save bytes by compressing them FURTHER (not that they aren’t compressed at all). It is super-conservative and tries re-compressing jpeg images at a quality level of 85 which should not have any perceivable visual difference.

5

It seems that when I applied subdomain like images1.domain.com/mod/ to those images will make them load longer. Now I removed it and just put /mod/xxx.png…

Any reason why this happen? I thought it could help to reduce loading time but not increase them…

http://www.webpagetest.org/result/121130_MH_1EM/1/details/

6

A new sub-domain (sharding) has some start-up cost where the browser has to do the DNS lookup and establish new connections. It usually only pays off if you have a LOT of static content that you need to serve.