1 What are the characteristics of vectors and bits? 2 What are the common color patterns? What are the characteristics? 3 What are the common file formats? What are the characteristics?

1, vector diagram: enlargement will not become empty, but bitmap enlargement will become empty. Vector diagram has nothing to do with pixels, because it describes the image according to geometric characteristics, and magnification does not affect the clarity;

Bitmap: An image consists of pixels, and each pixel is a unit of color. If the picture is enlarged, the pixels will be blurred.

2. Commonly used color modes are:

RGB: Most of the visible spectrum in nature can be represented by a mixture of red, green and blue light with different proportions and intensities. RGB stands for three colors: R stands for red, G stands for green and B stands for blue. The RGB model is also called the addition model, as shown in Figure 5. RGB mode is usually used for lighting, video and screen image editing.

CMKY:CMYK color mode is based on the light absorption characteristics of printing ink on paper. Each pixel in the image consists of indigo (C), magenta (M), yellow (Y) and black (K) in different proportions. Each printing ink in each pixel is assigned a percentage value, the brightest (highlighted) color is assigned a lower percentage value of printing ink color, and the darker (dark tone) color is assigned a higher percentage value. In a CMYK image, when the values of all four components are 0%, pure white will be produced. There are four channels in the image of CMYK color mode, and the graph we see is the composite effect of these four channels.

HSB:HSB color pattern is a set of color patterns based on the visual characteristics of human eyes in daily life, which is closest to the way human beings think about color recognition. The HSB color model uses hue (H), saturation (S) and brightness (B) to describe the basic characteristics of color.

Tone refers to the color reflected or transmitted by an object. On the standard color wheel of 0 to 360 degrees, hue is measured by position. Usually, tones are identified by color names, such as red, orange or green.

Saturation refers to the intensity or purity of color, expressed by the proportion of gray components in hue, with 0% being pure gray and 100% being completely saturated. On the standard color wheel, the saturation from the center position to the edge position increases.

Brightness refers to the relative lightness and darkness of a color. Generally, 0% is defined as black and 100% is defined as white.

The HSB color mode is easier to understand than the above two color modes. However, due to the limitation of equipment, it should be converted to RGB mode when displayed on the computer screen, and to CMYK mode when printed. This limits the use of HSB mode to some extent.

Lab color mode: It consists of photometric component (L) and two chroma components, namely component A (from green to red) and component B (from blue to yellow). Lab color mode has nothing to do with devices. No matter what devices (such as monitors, printers or scanners) are used to create or output images, the colors produced by this color mode are consistent.

Indexed color mode: Use up to 256 colors. When you convert an image to indexed color mode, you usually build a color palette to store and index the colors in the image. If the color in the original image does not appear in the palette, the program will select the closest color from the existing colors, or use the existing colors to simulate the color.

In indexed color mode, you can reduce the file size by limiting the number of colors in the palette while maintaining the same visual quality. Images in indexed mode are often needed in web pages.

Bitmap color mode: The image in bitmap mode consists of only black and white pixels, and each pixel is represented by a "bit". "Bit" has only two states: 0 means there is a bit, and 1 means there is no bit. Bitmap mode was mainly used in the early days for devices that could not recognize colors and grayscales. If it is necessary to represent gray scale, it needs to be simulated by point jitter.

Bitmap mode is usually used for character recognition. If you scan an image file that needs to be recognized by OCR (Optical Character Recognition) technology, you must convert the image into bitmap mode.

Gray-scale color mode: Gray-scale mode uses at most 256 gray levels to represent the image, and the brightness value of each pixel in the image is between 0 (black) and 255 (white). Gray value can also be expressed as the percentage of black ink coverage (0% for white and 100% for black).

When a color image is converted into a grayscale image, all the color information in the original image will be discarded. Compared with bitmap mode, gray mode can show high-quality image effect.

It should be noted that although some image processing software allows you to re-convert an image in gray mode into an image in color mode, the original lost color cannot be restored after conversion, and the image can only be re-colored. Therefore, when an image in color mode is converted into an image in gray mode, the backup file should be kept as much as possible.

3. Common file formats:

Grating image

BMP:Windows bitmap

Windows bitmaps can store a single raster image of any color depth (from black and white to 24-bit color). Windows bitmap file format is compatible with other Microsoft Windows programs. It does not support file compression, nor does it apply to web pages.

Generally speaking, the disadvantages of Windows bitmap file format outweigh the advantages. To ensure the quality of photo images, please use PNG files, JPEG files or TIFF files. BMP file is suitable for wallpaper in Windows.

Advantages:? 6? 1 BMP supports 1 bit to 24-bit color depth.

6? 1 BMP format is widely compatible with existing Windows programs (especially older programs).

Disadvantages:? 6? 1 BMP does not support compression, which will make the file very large.

6? Web browser does not support 1 BMP file.

Pcx: computer brush

PC brush pictures (also known as Z-Soft bitmaps) store a single raster image at any color depth. Brush drawing is more widely used in early Windows programs and programs based on MS-DOS. Brush drawing is compatible with many newer programs. PCX pictures support RLE internal compression.

Advantages:? 6? 1 PCX is a standard format between many Windows-based programs and MS-DOS-based programs.

6? 1 PCX supports internal compression.

Disadvantages:? 6? The Web browser does not support 1 PCX.

PNG: portable network graphics

PNG pictures store a single raster image at any color depth. PNG is a platform-independent format.

Advantages:? 6? 1 PNG supports advanced lossless compression.

6? 1 PNG supports alpha channel transparency.

6? 1 PNG supports gamma correction.

6? 1 PNG supports interleaving.

6? The latest Web browser supports 1 PNG.

Disadvantages:? 6? 1 Older browsers and programs may not support PNG files.

6? As an Internet file format, 1 provides less JPEG lossy compression.

6? As an Internet file format, PNG does not support multi-image files or animation files. GIF format supports multi-image files and animation files.

JPEG: Joint Photographic Experts Group

JPEG pictures store a single raster image in 24-bit color. JPEG is a platform-independent format that supports the highest level of compression. However, this compression is lossy. Progressive JPEG files support interleaving.

You can increase or decrease the compression level of JPEG files. However, the file size is at the expense of image quality. The compression ratio can be as high as 100: 1. (JPEG format can easily compress files at the ratio of 10: 1 to 20: 1, and the image quality will not decrease. ) JPEG compression can handle realistic photographic works well. However, JPEG compression can not provide ideal results for simple works with few colors, strong contrast, solid color borders or large solid color areas. Sometimes the compression ratio is as low as 5: 1, which seriously loses the integrity of the picture. The reason for this loss is that JPEG compression scheme can compress similar tones well, but JPEG compression scheme can not deal with strong differences in brightness or solid color areas well.

Advantages:? 6? 1 Photographic works or realistic works support advanced compression.

6? 1 You can control the file size with variable compression ratio.

6? 1 supports interleaving (for progressive JPEG files).

6? 1 JPEG widely supports Internet standards.

Disadvantages:? 6? Lossy compression of 1 will reduce the quality of the original image data.

6? 1 When you edit and resave a JPEG file, the quality of the original image data will be reduced due to JPEG mixing. This decline is cumulative.

6? 1 JPEG is not suitable for simple pictures with few colors, similar colors in a large area or obvious brightness difference.

GIF: graphic interchange format

GIF pictures store single raster image data or multiple raster image data in 8-bit colors or 256 colors. GIF pictures support transparent, compressed, interlaced and multi-image pictures (animated GIF).

GIF transparency is not alpha channel transparency, so it cannot support translucent effect. GIF compression is LZW compression, and the compression ratio is about 3: 1. GIF89a version of GIF file specification supports dynamic GIF.

Advantages:? 6? 1 GIF widely supports Internet standards.

6? 1 supports lossless compression and transparency.

6? 1 animated GIF is very popular, and it is easy to make with many GIF animation programs.

Disadvantages:? 6? 1 GIF only supports a 256-color palette, so detailed pictures and realistic photographic images will lose color information, but they look tonal.

6? 1 In most cases, lossless compression is not as good as JPEG format or PNG format.

6? 1 GIF supports limited transparency, with no translucent effect or fading effect (such as that provided by alpha channel transparency).

TIFF: tag image file format

TIFF stores a single raster image at any color depth. TIFF can be considered as the most widely supported graphic file format in the printing industry. TIFF supports optional compression and is not suitable for viewing in a Web browser.

TIFF format is an extensible format. This means that programmers can modify the original specification to add functionality or meet specific requirements. Modifying the specification may lead to incompatibility between different types of TIFF pictures.

Advantages:? 6? 1 TIFF is a widely supported format, especially between Macintosh computers and Windows-based computers.

6? 1 supports optional compression.

6? 1 Extensible format supports many optional functions.

Disadvantages:? 6? The Web browser does not support 1 TIFF.

6? The extensibility of 1 will lead to many different types of TIFF pictures. Not all TIFF files are compatible with all programs that support the basic TIFF standard.

Vector picture

DXF:AutoCAD graphic interchange file

DXF is a vector-based ASCII format used by Autodesk AutoCAD programs. AutoCAD can provide very detailed and fully extensible charts.

Advantages:? 6? 1 You can use AutoCAD to create very detailed and accurate charts and graphs.

6? 1 AutoCAD file is very popular in architecture, design and sculpture industries.

Disadvantages:? 6? 1 AutoCAD has limited support in Office, and Office supports AutoCAD versions before R 12.

6? 1 AutoCAD learning curve is steep. Please note that other graphics programs can also export DXF pictures.

Computer graphics metafile

CGM metafile can contain vector information and bitmap information. It is an international standardized file format used by many organizations and government agencies, including British Standards Institute (BSI), American National Standards Institute (ANSI) and US Department of Defense.

Advantages:? 6? 1 CGM is an international standard format.

CDR:CorelDRAW！

CorelDRAW！ Metafiles can contain vector information and bitmap information.

Advantages:? 6? 1 CDR is widely used in prepress industry and art design industry.

Disadvantages:? 6? 1 CDR has limited support in Office, and Office supports CorelDRAW! Version 6 and earlier.

WMF: window metafile

Windows metafile is a 16-bit Tu Tu metafile format, which can contain vector information and bitmap information. It is optimized for the Windows operating system.

Advantages:? 6? 1 WMF is the standard format of Windows, which can be used well in office.

EPS: encapsulated PostScript

"Encapsulated PostScript" format is a special printer description language, which can describe vector information and bitmap information.

Advantages:? 6? 1 EPS can accurately render the effect on any PostScript printer.

6? 1 EPS is an industry standard format.

Disadvantages:? 6? 1 The screen display may be inconsistent with the output display. The screen display may be low resolution, may be a different image, or just a placeholder image.

6? 1 EPS file is used for output. They are not the most suitable formats for displaying information on the screen.

EMF: enhanced metafile

Enhanced metafile is a 32-bit format, which can contain vector information and bitmap information. This format is an improvement on the "Windows Metafile Format" and contains some extended functions, such as the following:

6? 1 Built-in zoom information

6? 1 Built-in description saved with file

6? 1 improvement of color palette and equipment independence

The EMF format is extensible, which means that programmers can modify the original specification to add functions or meet specific requirements. This modification may lead to incompatibility between different types of EMF pictures.

Advantages:? 6? 1 Extensible file format

6? Compared with WMF, 1 has improved functions.

Disadvantages:? 6? The extensibility of 1 will lead to many different types of EMF pictures, and not all EMF files are compatible with all programs that support EMF standards.

PICT: Macintosh pictures

PICT file is a 32-bit bitmap metafile format for Macintosh computers. PICT file uses RLE internal compression, and the effect is quite good. If QuickTime is installed, PICT files support JPEG compression (Macintosh only).

Advantages:? 6? 1 PICT is the best file format for Macintosh computer screen display.

6? 1 PICT is the best output format when outputting from a Macintosh computer to a non-PostScript printer.

Disadvantages:? 6? When 1 moves them between platforms, fonts may not be displayed correctly.

6? 1 QuickTime must be installed to view some PICT files correctly.