Goal
- Decrease the amount of data to download.
- Improve page display speed.
- Decrease the energy impact related to the consultation of the site.
Implementation
For image preview vignettes, use specific versions of them and not original images resized using their HTML attributes or CSS properties.
Control
For all HTML images present in the source code or generated via javascript:
- Check that they do not have CSS
height
orwidth
properties which modify the apparent size of the images in relation to their actual dimensions.To do this, use "deactivate all CSS styles" using a web development tool to find images whose dimensions change after deactivating CSS styles. - Also check that the dimensions indicated in the
width
andheight
attributes of the generated HTML code correspond to the actual dimensions of the image using a development tool.
For example, the following will be invalidated:
- An image of the type <img height="300" width="600" class="thumb"/> if the
.thumb
class imposes the CSS propertiesheight: 100px
andwidth: auto
. - An image of the type <img height="100" width="200"/> if the actual dimensions of the image are 300px high and 600px wide.