Windows 8.1 is just a few weeks away from its official October 18th launch date and Microsoft has begun promoting some of the improvements it has made to Internet Explorer 11. This week, Microsoft has revealed that the browser has a new image decoding pipeline, claiming it greatly increases the speed of loading JPG images from websites.
In a post on the official IE blog, Microsoft says that images take up 61 percent of all of the data downloaded from websites, and that 47 percent of web images are JPG files. Microsoft claims that their new method loads JPG images up to 45 percent faster in IE11, on Windows 8.1, compared with older IE versions.
The blog goes into some technical details on how JPG files are normally encoded, starting from its RGB (red, green and blue) color components, shown above, to the YCbCr color space. Then the image size is compressed via chroma subsampling, followed by discrete cosine transformation, quantization, and Huffman encoding processes to get the final encoded JPG file.
Naturally, decoding a JPG image on a web browser means taking the encoding process and reversing it. Older versions of IE would run the first steps on the CPU and then run the final RGB bitmap in the GPU for rendering. IE11 on Windows 8.1 does things differently by giving the GPU more of the earlier decoding duties. The blog states:
IE11 decodes the JPG image into the chroma subsampled YCbCr color space on the CPU, but then does the chroma upsampling and YCbCr to RGB color conversion steps on the GPU at draw time, where it can happen much faster and in parallel. This process frees CPU time to perform other operations, as the CPU is a common bottleneck in modern sites and apps. In addition to the decode time improvements, copying the much smaller YCbCr image to the GPU reduces the amount of memory that is copied and stored on the GPU (a limited resource). Using less CPU and memory also reduces power consumption and increases data locality.
The JPG image of a barn located in the Grand Tetons Mountains, that's shown above, took 31.9ms to decode in IE10 along with 81.5ms to draw the same image in the browser. With IE11 on Windows 8.1, Microsoft says it took just 17.9ms to decode the same image and 57.5ms to draw that JPG file.
While IE11 users should see the benefits of this new image decoding method with no extra effort, Microsoft is recommending web developers compress their JPG images on their sites by using either 4:2:2 or 4:2:0 chroma subsampling modes so that their images have the best chance of being used by IE11's new downloading features.
Source: Microsoft | Image via Microsoft