A brief description of common Web page image format: bmp/jpg/gif

One, BMP image files

The BMP image file, which was first applied to the Windows operating system, is the standard image file format in the Windows operating system and is the simplest image format.

BMP image format is very simple, only the most basic image data storage function, can store each pixel 1-bit, 4-bit, 8-bit and 24-bit bitmap. Although the information it provides is too simple, but because of the popularity of Windows and BMP itself has a simple format, standard, transparent features, BMP image File format has been promoted, it is generally applied to the Windows system screen display and some simple image system.

The feature of this format is that the information contained in the image is richer and almost uncompressed, but it has the inherent disadvantage of taking up too much disk space. It is rarely used in Web pages.

A 24-bit 800x600 BMP format graphic file size:

800x600x3byte=1440000byte≈1440byte≈1.44m

Second, GIF image files

GIF format is characterized by high compression ratio, less disk space, so this image in the Web page to use a lot.

Two versions of GIF:

GIF87A: Simply used to store a single still image.

GIF89A: A number of still images can be stored at the same time in order to form a continuous animation, to support the 2D animation format. You can specify transparent areas so that the image has an extraordinary display effect, which makes the GIF more beautiful. Most of the color animation files used on the Internet today are in this format. Pixel painting. QQ Show, QQ space and so on n more things.

GIF image format also increases the fade way, that is, in the image transmission process, the user can first see the outline of the image, and then as the transmission process continues to gradually see the details of the image, thus adapting to the user's "from hazy to clear" viewing psychology.

Because of the 8-bit storage format limit, so that it can not store more than 256 colors of the image, suitable for the total number of pictures with less than 256 colors.

The best way to show the GIF format:

If the color is less than 256, the palette can be selected as "precise".

Do not select "distorted".

In general, the palette chooses "best fit" and the maximum number of colors is selected "256". If the color is slightly more than 256 colors, you can set the jitter to "100%".

To prevent jagged edges, do not need to be transparent when, as far as possible opaque.

A little trick:

If you want to export slices of the Web page into GIF format, if the color is rich, it is not appropriate to export together, but should be sliced one one of the export. Buttons for the following figure:

Third, JPEG image files

The JPEG file has an extension of. jpg or. jpeg, its compression technology is very advanced, it uses lossy compression method to remove redundant images and color data, obtain extremely high compression rate and can display very rich vivid images, in other words, can use the least disk space to get better image quality.

JPEG 2000 is also developed by the JPEG organization, which has a new generation of static image compression technology with higher compression rates and newer features than JPEG.

JPEG2000 as an upgraded version of JPEG, its compression rate is about 30% higher than JPEG. Unlike JPEG, JPEG2000 supports both lossy and lossless compression, while JPEG can only support lossy compression. Lossless compression is useful for saving important pictures.

An extremely important feature of JPEG2000 is its ability to achieve progressive transmission, which is similar to GIF's "fade", that is, the first transmission of image contour, and then gradually transmit data, constantly improve image quality, so that the image from hazy to clear display.

In addition, JPEG2000 also supports the so-called "area of interest" feature, you can arbitrarily specify the image of your area of interest compression quality, you can also select the specified part of the first decompression.

Use the note point of a JPG image: Find a balance between the image quality and the file size. The general 80% compression rate is more suitable for use in the Web page.