Optimization suggestions for CSS images

This article mainly introduces some relevant suggestions for CSS image optimization. It mainly provides a brief introduction to Sprites image integration technology. Friends in need can refer to it

CSS image optimization is to compress the size of the image as much as possible. Speeds up page loading, which is useful for large websites. Don't underestimate it, it can greatly improve web page loading speed. The method usually used by everyone is css sprites.

The purpose of CSS Sprites (image integration technology) is to reduce the number of requests to the server by integrating images, thereby speeding up page loading. I think many people are already using this technology. Let me give you a brief introduction and summarize some of my techniques when using CSS sprites.
　 CSS Sprites implementation method:

First integrate the small pictures into a large picture, and then position the background according to the position of the specific icon on the big picture.
　 Summary of CSS Sprites technical points:

1. When integrating small pictures, follow the order from top to bottom, rather than arranging one picture next to another from left to right. Arranging the value of background-position in this way is clear at a glance, which is much more convenient when writing CSS. It is also for the sake of later maintenance. Imagine that if the size of one of the images is changed during later maintenance, the background-position of all surrounding elements will change accordingly, which will be a headache.

　2. When integrating small pictures, try to be as far left or right as possible. These two positions are very flexible and are very suitable for placing icons in front of text. When writing styles, they will not be interfered by other CSS Sprites images. Based on point 1, we can start integrating the pictures from top to bottom along the leftmost and rightmost sides.

　3. It is not recommended to leave gaps above and below different small pictures. Because this will cause the image size to increase and thus increase the file size. These gaps are not necessary.

　4. Combining images with close or identical colors can reduce the number of colors, because the file size of images with a small number of colors will be relatively small.
Image optimization:

After we integrate all the small pictures into one big picture, we must start to consider the issue of image optimization. You can take a look at the current file size of the image. Is there something unsatisfactory? It doesn’t matter. The following steps can solve it.

Since the background of the integrated large image is basically completely transparent, we will save it in png format. You may say that the file size of gif is smaller than that of png. Don’t we need to optimize it? Why not gif? Because GIF images will have a lot of aliases when processing curves such as rounded corners, or diagonal lines, which we don't want to see. And some small picture pixels that are close to white may be lost. Moreover, we can also find a format smaller than gif, which is the PNG8 format I will introduce today.

For non-animated GIFs, it is recommended to use PNG8 because it can achieve the same effect as the original png image, and can save you 10%-30% of the file size, even more than gif images.
　How to convert pictures to png8 format

　1. Picture preparation: No matter what drawing software you use to draw the picture, just follow the normal operation and save it in png format. There is no conversion operation to png8 in photoshop, so we need to turn to fireworks.

　2. Open the integrated large image in fireworks.

　3. Select File—Image Preview.

　4. Select PNG8 in the "Format" drop-down box. There is no need to select anything else. Just click the "Export" button to select the path.

It’s very simple~ Take a look at the size of your png8 picture and compare it with the previous picture. You will be surprised! ~~Looking at the picture quality, it is simply perfect~~

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