Format characteristics of mobile phone pictures

There are 9 formats of mobile phone pictures, including BMP, JPEG, JP2, GIF, TIFF, PNG, EXIF, WBMP and MBM.

① BMP-BMP image file format

BMP: BMP is an image file format that has nothing to do with hardware devices, and it is also a standard bitmap format under Windows system, which is widely used. It uses bitmap storage format and does not use any other compression except image depth, so BMP files take up a lot of space. The image depth of BMP file can be selected as lbit, 4bit, 8bit and 24bit. A typical BMP image file consists of three parts: a bitmap file header data structure, which contains information such as the type and display content of the BMP image file; Bitmap information data structure, including BMP image width, height, compression mode, defined color and other information. When data is stored in a BMP file, images are scanned from left to right and from bottom to top. Its biggest advantage is that it can be "accepted" by most software, which can be called a universal format.

BMP is a popular image format in the past. Now, when PC runs Window, BMP (Window bitmap) image is mainly used as wallpaper. Programmers sometimes use BMP images in their software help functions. Some people simply refer to BMP images as bitmap images, but this word is sometimes confused. Usually, a pixel-based image is called a bitmap image. ) BMP can provide lossless compression, and the compression method is RLE (Run-length Coding), which is an excellent choice when creating wallpaper image files. Sometimes, when looking for wallpaper pictures saved as RLE compressed files, there will be recognition errors in Window. Therefore, it is best to turn off RLE compression function before use.

② JPG-JPEG file format

JPEG is the abbreviation of Joint Photographic Experts Group (the name of the organization that developed this format), and the file name is ". Jpg "or" jpeg”。 JPEG format is one of the most widely used formats at present, and almost all image programs in Mac and Windows systems can open and save JPEG images. JPEG is also one of the two main file formats used for image processing on the World Wide Web (JPEG and GIF, JPEG files are generally smaller than GIF files).

One advantage of JPEG format is that it can compress image data. JPEG is a lossy compression format, which can compress images in a small storage space. Repeated or unimportant data in images will be lost, so it is easy to damage image data. Especially, if the compression ratio is too high, the quality of the restored image after final decompression will obviously decrease. If you pursue high-quality images, you should not use too high compression ratio. But JPEG compression technology is very advanced. It uses lossy compression to remove redundant image data, and can display very rich and vivid images at the same time, in other words, it can obtain better image quality with the least disk space. Moreover, JPEG is a very flexible format with the function of adjusting image quality. It allows files to be compressed at different compression ratios and supports multiple compression levels. The compression ratio is usually between 10: 1 and 40: 1. The higher the compression ratio, the lower the mass. On the contrary, the smaller the compression ratio, the better the quality.

Therefore, JPEG image files are relatively small. The smaller the image file, the more disk space will be saved, and the more time will be saved when downloading from the Internet. The problem is that JPEG uses a lossy compression scheme. This means that some image data will be lost in the compression process. Every time an image is opened, edited and saved, it is repeatedly compressed, resulting in more losses. JPEG supports extremely high compression ratio. JPEG format saves storage space by accurately recording the brightness of each pixel and averaging its hue, so it has little impact on image quality, so it can obtain better image quality with relatively small disk space. You can choose different compression ratios to compress JPEG files, that is, both compression ratio and image quality are optional.

JPEG format can support 16M color, can reproduce full-color images well, and is suitable for storing photographic images. Because the compression algorithm of JPEG format is to balance the brightness and color between pixels, it is more beneficial to express the image with gradual color change and unclear outline. JPEG (Still Image Compression Standard) image format can support 24-bit full color. It accurately records the brightness of each pixel, but it compresses the image in a balanced tone, so that our naked eyes can't clearly distinguish it. In fact, it is recording the description of the image, rather than compressing it when it appears. The web browser or image editing software used by the viewer will interpret the recorded description as a dot matrix image, so that it looks very similar to the original image.

The accuracy of the reproduced image depends on the compression ratio you choose. You can choose JPEG compression ratio from most image editing tools. These interpreted tones are put into the template area one by one in a diffused shape. Because these template areas will overlap with each other, it is difficult to clearly distinguish the boundaries of different colors in the case of a lot of data. However, this technique is very suitable for photographic works with gradual color changes and inconspicuous edges. For example, tropical birds are particularly suitable for JPEG format.

When saving an image in JPEG format, you usually encounter a dialog box as shown in the figure, so you need to determine the amount of compression you want to use. In order to ensure the minimum data loss and the best printed image effect, the highest quality setting (minimum compression at this time) should be selected. For images on the Web, you can use a medium-quality compression setting. If you need to save an image in JPEG format, you'd better wait until the final editing of the image is completed. In this way, you only need to compress the image once, and you can keep the data loss to a minimum. When stored in JPEG format in Photoshop software, the compression level of 1 1 is provided, which is represented by 0- 10. Level 0 has the highest compression ratio and the worst image quality. The compression ratio can reach 5: 1 even if the quality maintenance with almost no loss of details is adopted. 4. When saving in BMP format, the image file of 28 MB is obtained, while when saving in JPG format, it is only 178KB, and the compression ratio reaches 24: 1. After many comparisons, eight-level compression is the best ratio of storage space and image quality.

③ JP2-JPEG2000 file format

As an upgraded version of JPEG, JPEG2000 has a compression ratio about 30% higher than that of JPEG, and supports both lossy and lossless compression. An extremely important feature of JPEG2000 format is that it can realize progressive transmission, that is, the outline of the image is transmitted first, and then the data is transmitted step by step, so as to continuously improve the image quality and make the image display from hazy to clear. In addition, JPEG2000 also supports the so-called region of interest function, which can arbitrarily specify the compression quality of the region of interest on the image, or select the specified part to decompress first.

Compared with JPEG, JPEG2000 has obvious advantages and backward compatibility, so it can replace the traditional JPEG format. JPEG2000 can be applied to both traditional JPEG market, such as scanners and digital cameras, and emerging fields, such as network transmission and wireless communication.

④ GIF-GIF file format

GIF (Graphic Interchange Format) originally means "Image Interchange Format", which is an image file format developed by CompuServe Company in 1987. The data of GIF file is a continuous tone lossless compression format based on LZW algorithm. Its compression ratio is generally around 50%, which does not belong to any application. Almost all related software supports it, and a large number of software in the public domain are using GIF image files. The data of GIF image file is compressed by variable length compression algorithm. Therefore, the image depth of GIF varies from lbit to 8bit, which means that GIF can support 256-color images at most. Another feature of GIF format is that images with multiple colors can be stored in a GIF file. If the data of multiple images stored in a file are read out one by one and displayed on the screen, the simplest animation can be formed.

GIF (Image Interchange Format) of CompuServe compresses image files in two ways: First, it uses an encoding method called lem pel-Clark, which treats pixels with similar colors in the same row and column as a unit. Secondly, it limits the indexed color of the document itself. In other words, a GIF file cannot have more than 256 colors, so you must reduce the colors used in the image before using it. This is why the GIF format is not suitable for photos or high-color images. Although GIF has few colors, it can be greatly compressed: colors below 128 or 128 are represented by 7-bit data; 64 colors are represented by 6-bit data. In this way, GIF is the best choice for simple line drawings, which means that it has its own advantages and disadvantages in adding or deleting colors. The image in GIF format can only reach 256 colors at most, which is "not enough" for images with transition colors and gradient colors, but the compression rate in GIF format is very high. For images with less than 256 colors, the lossless compression in GIF format almost maintains the clarity of the original image. This is also one of the characteristics of GIF format pictures.

GIF: It can be divided into static GIF and animated GIF. It supports transparent background images and is suitable for various operating systems. Its "body shape" is very small, and many small animations on the Internet are in GIF format. In fact, GIF is to save multiple pictures as a picture file to form an animation, so in the final analysis, GIF is still a picture file format.

GIF decoding is faster, because interlaced GIF images can be divided into four scans when decoding and displaying. Although the first scan only showed one-eighth of the whole image, and the second scan only showed 1/4, it has already shown an overview of the whole image. When displaying GIF pictures, staggered pictures will make you feel that its display speed seems to be faster than other pictures, which is the advantage of staggered storage.

⑤ TIFF-TIFF image file format

TIFF (Tag Information File Format) is a general image file format developed by Aldus and Microsoft for desktop publishing system. It was designed by Aldus Company in 1986, and it is a lossless 24-bit color image format. It can keep the color and lines of the original image, but it takes up a lot of space. TIFF is designed for cross-platform use, so it is accepted by most systems and image editing software. The only drawback is that some versions of TIFF are incompatible with each other, so different image editing software may not be able to read each other's TIFF files. But this file has been solved in new popular software such as Photoshop and CorelDraw.

The image file in TIFF format is very large. For example, a 2-megapixel image takes up almost 6MB of memory capacity, so TIFF is usually used for more professional purposes, such as book publishing and posters. , which is rarely used on the Internet.

TIFF format is flexible and changeable. It defines four different formats: TIFF-B is suitable for binary images, TIFF-G is suitable for black and white gray images; TIFF-P is suitable for color images with palette; TIFF-R is suitable for RGB true color images.

TIFF supports a variety of coding methods, including RGB compression, RLE compression and JPEG compression.

TIFF image files consist of three data structures, namely, a file header, one or more directories containing marker pointers called IFD, and the data itself. TIFF image file format is one of the most complicated image file formats, which is extensible, convenient and modifiable, and can be provided for image editing programs running in IBMPC and other environments.

Although most programs, not all programs support LZW compressed Tiff images. If there is a problem when opening a TIFF image, it may be due to compression. At this time, you can try to open the saved image with other programs, so you can cancel the compression.

⑥ PNG-PNG image file format

The full name of PNG is portable network graphics format. This is a very new file format, developed by Web Graphics. At present, the most undistorted format is PNG. It correctly and accurately compresses 24-bit or 32-bit color images-a new alpha or transparency that supports 24-bit images plus 8 bits. It can also compress images with indexed color of 256 or less and support gamma correction. Even better, it is designed into a network format. Although only recent applications can read or create PNG files correctly, the browser of ACDSee 4.0 can support this format even under imperfect environment.

PNG format is different from GIF format and is not limited by 256 colors. Unlike JPEG format, it does not use lossy compression. The advantage of this format is that you can get high-quality images; The disadvantage is that your file is relatively large, which means it takes longer to download your pictures online. PNG is similar to JPG format. There are many pictures in this format on the webpage. The compression ratio is higher than GIF, which supports image transparency. You can use the Alpha channel to adjust the transparency of the image. PNG can provide lossless compressed image files that are 30% shorter than GIF. It also provides 24-bit and 48-bit true color image support and many other technical support. Because PNG is very new, not all programs can use it to store image files at present, but Photoshop can handle PNG image files and can also store them in PNG image file format.

⑦ EXIF-EXIF format

EXIF format is a digital camera image file format advocated by Fuji Company in 1994. In fact, it is the same as JPEG format. The difference is that it can also store exposure data such as shooting date, aperture, shutter and flash data, incidental information and small-size images.

8 WBMP-WBMP format

Wireless bitmap (WBMP) is a standard image format used by mobile computer devices. This format is specially used for WAP pages. WBMP supports 1 bit color, that is, WBMP images only contain black and white pixels, and cannot be made too large for correct display in wap phones.

Pet-name ruby ⑨MBM-MBM format

MBM format file is a bitmap file format of Symbian OS, which is a multi-bitmap file. Window bitmap uses bitmap conversion tool bmconv to create MBM. Since an MBM file may contain multiple bitmaps, bmconv will also generate a bitmap header file MBG, which provides an ID for accessing bitmaps. When loading a bitmap from an MBM file, the corresponding header file should be included, and the appropriate identifier should be used as the parameter of the method of loading the bitmap.

At present, there are nine commonly used formats supported by mobile phones on the market. I'm sure you know exactly which format to choose. Let's talk about the definition of standby screen first. The clarity of a picture is not determined by its size KB, but by: 1, the clarity of the source of the picture itself; 2, the number of pictures; 3. Modify the magnification of the picture; 4. Whether the resolution of the picture matches the resolution supported by the mobile phone; 5. The matching degree between the color of the picture and the mobile phone; 6, the format of the picture. It's decided.