Selecting Image File Format: Improving Image Processing Quality (I)

Each beautiful wallpaper of the computer can express personal sentiment and style; when we design web pages, we often miss the decoration of the pictures. So what are the images that we normally touch? What are the common image file formats?

One, BMP format

BMP is an abbreviation of English Bitmap. It is a standard image file format in the Windows operating system and can be supported by various Windows applications. With the popularity of the Windows operating system and the development of rich Windows applications, the BMP bitmap format is naturally widely used. The characteristic of this format is that the contained image information is rich and hardly compressed, but this leads to its inherent disadvantage - it takes up too much disk space. Therefore, at present, BMP is more popular on stand-alone machines.

Second, the GIF format

GIF is an acronym for Graphics Interchange Format. As the name suggests, this format is used to exchange images. In fact, in the 1980s, CompuServe, a well-known online information service organization in the United States, developed the GIF image format in response to the limitations of network transmission bandwidth at that time.

The GIF format is characterized by high compression ratio and less disk space usage, so this image format has rapidly been widely used.

The original GIF was simply used to store a single still image (called GIF87a). Later, as the technology developed, several still images could be stored at the same time to form a continuous animation, making it one of the few to support 2D animation at the time. One of the formats (called GIF89a), and transparent areas can be specified in the GIF89a image, so that the image has an extraordinary display effect, which makes the GIF more full of scenery. At present, most of the color animation files used on the Internet are mostly files of this format, also known as GIF89a format files.

In addition, taking into account the actual situation in the network transmission, the GIF image format has also increased the fade-out mode, that is, during the image transmission process, the user can first see the outline of the image, and then gradually along with the transmission process. See the details in the image, so as to adapt to the user's "from ambiguous to clear" viewing psychology. At present, most color animation files used on the Internet are mostly files in this format.

However, the GIF has a minor drawback: it cannot store more than 256 colors. However, this format is still popular on the Internet, which is inseparable from the advantages of short GIF image files, fast download speeds, and the ability to compose animations with many image files of the same size.

Three, JPEG format

JPEG is also a common image format. It was developed by the Joint Photographic Experts Group and is named "ISO 10918-1". JPEG is just a common name. JPEG files have the extension .jpg or .jpeg, and their compression technology is very advanced. It uses lossy compression to remove redundant images and color data, and achieves extremely high compression rates while displaying very rich and vivid images. In other words, you can get better image quality with the least amount of disk space.

At the same time JPEG is a very flexible format, with the ability to adjust the image quality, allowing you to compress this file with different compression ratios. For example, we can compress a 1.37MB BMP bitmap file to 20.3KB. Of course we can find a balance between image quality and file size.

Due to the excellent quality and outstanding performance of JPEG, its application is also very extensive, especially on the network and CD-ROM readings, certainly can find its shadow. Currently, all types of browsers support the JPEG image format. Because the file size of the JPEG format is small and the downloading speed is fast, it is possible for a Web page to provide a large amount of beautiful images with a short download time, and JPEG becomes a logical choice at the same time. The most popular image format on the web.

Fourth, JPEG2000 format

JPEG 2000 was also developed by the JPEG organization. It has a formal name called "ISO 15444". Compared with JPEG, it has a new generation of still image compression technology with higher compression rate and more new features.

JPEG2000 is an upgraded version of JPEG and its compression rate is about 30% higher than that of JPEG. Unlike JPEG, JPEG2000 supports both lossy and lossless compression, while JPEG only supports lossy compression. Lossless compression is very useful for saving some important pictures. One of the most important features of JPEG2000 is its ability to achieve progressive transmission. This is similar to the "fade-out" of GIF. It transfers the contour of the image first, then gradually transmits the data, and continuously improves the image quality. To show clearly, instead of being like JPEG now, slowly from top to bottom.

In addition, JPEG2000 also supports the so-called "region of interest" feature. You can arbitrarily specify the compression quality of the region of interest on your image, and you can also select the specified portion to decompress first.

JPEG 2000 has obvious advantages compared to JPEG and is backward compatible, so replacing the traditional JPEG format is just around the corner.

JPEG2000 can be applied to the traditional JPEG market, such as scanners, digital cameras, etc. It can also be applied in emerging fields such as network transmission, wireless communication and so on. (to be continued)