Computer Graphics and Image File Formats (1)

Types of Computer Graphics <br> Vector images are well-suited to technical illustrations, but generally do not provide the characteristics of a photo realistic image to be produced. The quality of the focus and lighting is difficult to obtain in a vector image. On the other hand, certain types of bitmap images, such as 1-bit/pixel bitmaps, cannot be successfully used to draw different dimensions that vectors can express.

A good way to compare similarities and differences between different types of computer images is to use a picture tree that describes the type of picture. At the root or base level of a computer image tree is a single image or set of images. On the first level branch of the picture tree, static digital images can be divided into vector images and bitmap images.

A vector graphic is also called face-to-face drawing because an image file of this type contains separate, separate picture elements and can be freely recombined without restriction. Vector graphics are also resolution-independent graphics - they can enlarge a nut to a very large extent, and the image still has the same visual detail, sharpness, and smooth edges when printed. This resolution independence is achieved because vector graphics do not involve real conversions when stored in a file format. A vector graphic exists in some mathematical formulas that are only converted to the screen each time the graphic is edited, and are only converted to the printer after specifying the image size and resolution.

2. The branch of the bitmap

Bitmap images are more likely to give a photo-like feel because their lighting, transparency, and depth of quality are all successfully demonstrated.

Bitmap images are not purely mathematical formulas to create and store. The user must specify the resolution and image size when deciding to create this type of graphics. The most common way people create a bitmap image is by scanning a photo. It is also possible to create a bitmap image by filling a imaginary grid with color dots or pixels through a program of a different drawing type from the vector drawing program. A bitmap image can express the wonderful subtleties of the represented image because it does not rely on any contours and fill mathematical formulas used in the vector.

Bitmap images have four branches. These branches depend on the performance of the image type and the organization of the bitmap information that makes up a graphic.

<1> Line graphics

When a pencil and pen and ink are scanned into the computer, the scanner settings can be specified as the so-called line chart. Software developers and artists also refer to this setup as black and white, bitmap, and 1-bit depth, (a bit, or a binary number).

When set to the line graph mode, the scanner views the source image with one-bit color performance. If the sample of the source image is a black area, the scanner considers it to be 0 and turns off the pixel. Conversely, if it is a white area, the scanner thinks it is 1, turning on the pixels. The original image area between black and white values ​​is given black or white pixels - there are no other values ​​in the online image acquisition mode. This is why a color image scanned in the form of a line graph is as if it were copied multiple times in the digital image state.

<2> Grayscale image

Grayscale images are represented by eight bits of information per pixel compared to one bit per pixel of a line graph, and information for a grayscale image is organized in a different manner to accommodate enhanced color performance. The grayscale image mode provides two 8th power 256 expression image detail luminance values. The information in a grayscale image is organized into a single channel.

<3> Color image

Some scanners sample a source image in 24-bit RGB (red, green, blue) mode, which can sample up to 16.7 million different colors in a scan of the source image. Although a source image may contain only a small amount of color, the scanner samples the data and expresses it in a pattern that can display 16.7 million colors.

<4> Index color

The color information of an image should be described and organized in a way that a computer program can grasp. For example, when scanning an image in RGB mode, Photoshop thinks that the resulting pixel has 24 bits per pixel performance. The colors in an RGB image are usually organized in three separate channels—red, green, and blue—each. Each channel has 256 levels of luminance fields to express the presence of red, green, and blue components.

However, the index color is not organized in three different color channels; instead, it contains only one color channel, where the red, green, and blue components of each pixel are written in a color table with a fixed value. Each indexed color image file contains a special header that informs the application of the color table of the image and where the color is mapped onto the pixel.

Although indexed color images provide computers with a quick and convenient color management system, indexing color images - because of their limited color table - cannot express photo images in real life.

Indexed colors are also often referred to as mapped colors, and indexed color images are not directly obtained but are indirectly created. In the indexed color mode, the colors are pre-defined just like the color crayons, and the user can only get a limited set when coloring. The reason for this limitation is that the color palette of the images cannot effectively describe more than 256 individual colors. value.