In the worst case, the browser will load an image completely before it starts loading the next one. Progressive JPEGs alone are therefore not the solution to give the user the fastest possible impression of the page. This is because modern browsers only allow six simultaneous connections to a domain. If your website consists of many JPEGs, you will notice that even progressive JPEGs load one after the other. For files larger than 10 kB, there is a 94 percent probability of a smaller image when using progressive mode according to Stoyan Stefanov of the Yahoo development team. In addition to the better user experience provided by the appearance that is displayed more quickly, progressive JPEGs are usually also smaller than their baseline-encoded counterparts. Baseline mode ( Large preview) Progressive mode ( Large preview) Instead of having the image built up from top to bottom during loading (baseline mode), a blurred image can be displayed very quickly, which gradually becomes sharper and sharper (progressive mode).
JPEG files, for which lazy loading is mostly used, have the possibility, according to the specification, to store the data contained in them in such a way that first the coarse and then the detailed image contents are displayed. What if you could present a preview image to the website visitor without having to load additional data? This will be displayed blurred and later replaced by the original image. What both have in common is that you first generate a low-quality preview image. Low Quality Image Preview (LQIP) and the SVG-based variant SQIP are the two predominant techniques for lazy image loading. The Embedded Image Preview (EIP) technique introduced in this article allows us to load preview images during lazy loading using progressive JPEGs, Ajax and HTTP range requests without having to transfer additional data.
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