0Responsive background images for websites

I’ve recently been updat­ing my web­sites and web serv­er and adding a new site (LoveCrete.org). I wanted to have a back­ground image on LoveCrete and real­ised that of course 1 size does­n’t fit all screens. Here is a sum­mary of what my think­ing was and what I did to cater for the numer­ous screen sizes and orientations.

Which orientation

I star­ted by mak­ing myself a little table of all the com­mon res­ol­u­tions used on PCs and tab­lets (in hori­zont­al ori­ent­a­tion). I decided to focus on this because most images are avail­able in land­scape so this is a sens­ible place to start.

I decided that I would place images cent­rally on the page and let the edges be lost off the edge of the screen in some instances. When a phone is used in por­trait ori­ent­a­tion it will load the image based on height (not width) and will lose a lot from both edge of the image. Doing it any oth­er way would mean need­ing images cropped to a totally dif­fer­ent shape or hav­ing a land­scape image “tile” on a tall screen, which is not desirable.

The ratios of the max­im­um size image to make in each group were all around 1.6 with a few a bit high­er. To keep things sim­pler I decided to use a ratio of 16:10 for all images and came up with sizes to make accordingly.

This means in most cases the image will not be a per­fect fit to the screen size, but all screens will get some­thing very close and no screen will end up with some­thing too small. It also means a source image can be cropped to 16:10 once and then mul­tiple sizes eas­ily created

Common landscape resolution groups

As you can see I have grouped quite a few res­ol­u­tions and will then make 1 image that will cov­er all heights up to the largest height in that group. I will make sure the image is also wide enough for the max­im­um width such a height might be paired with on a nor­mal screen. I haven’t taken account of unusu­al con­fig­ur­a­tions like 21:9 mon­it­ors or mul­tiple screens — there has to be a lim­it somewhere!

Because CSS uses the view­port or browser size and not the screen size land­scape screens need to use width rather than height — as on most sys­tems the top and bot­tom lose space to title bars etc whilst the width is usu­ally max­im­ised. How­ever, for por­trait dis­plays it is bet­ter to use the height prop­erty. This can be done as CSS can identi­fy the screen orientation

The CSS used then looks as follows

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