### 计算机代写|图像处理代写Image Processing代考|ECE6123

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• Statistical Inference 统计推断
• Statistical Computing 统计计算
• (Generalized) Linear Models 广义线性模型
• Statistical Machine Learning 统计机器学习
• Longitudinal Data Analysis 纵向数据分析
• Foundations of Data Science 数据科学基础

## 计算机代写|图像处理代写Image Processing代考|Half-Tone Output Technology

To further understand the relationship between image spatial resolution and amplitude resolution and image visual quality, let’s look at the half-tone technology and dithering technology commonly used in image printouts. Their principles are also very helpful for understanding the concept of images and pixels.
1.1.4.1 Half-Tone Output Technology
General printing equipment can only directly output binary images. For example, the grayscale output of a laser printer has only two levels (either printing, outputting black; or not printing, outputting white). To output a grayscale image on a binary image output device and maintain its original grayscale level, a technique called half-tone output is often used.
Half-tone output technology can be regarded as a technology that converts grayscale images into binary images. It converts various gray scales in the intended output image into a binary point mode so that the grayscale image can be output by a printing device that can only directly output binary points. At the same time, it takes advantage of the integrated characteristics of the human eye, by controlling the form of the output binary point pattern (including number, size, shape, etc.) to give people a visual sense of multiple gray levels. In other words, the image output by the half-tone output technology is still a binary image at a very fine scale, but due to the spatial local averaging effect of the eyes, what is perceived is a grayscale image at a coarser scale. For example, in a binary image, the gray level of each pixel is only white or black, but from a certain distance, the unit perceived by the human cyc is composed of multiple pixcls, then the gray level perccived by the human eye is the average gray level of all pixels in this unit (proportional to the number of black pixcls).

Half-tone output technology is mainly divided into two types: amplitude modulation (AM) technology and frequency modulation (FM) technology, which will be introduced separately below.

## 计算机代写|图像处理代写Image Processing代考|Dithering Technology

Half-tone output technology improves the resolution of the image amplitude by reducing the spatial resolution of the image or sacrificing the number of spatial points of the image to increase the number of gray levels of the image. It can be seen from the above discussion that if one wants to output an image with more gray levels, the spatial resolution of the image will be greatly reduced; if one wants to maintain a certain spatial resolution, the output gray level will be relatively small. That is, if one wants to preserve the spatial details, the number of gray levels cannot be too much. However, when the gray level of an image is relatively small, the visual quality of the image will be relatively poor, such as the appearance of false contours. To improve the quality of the image, dithering technology is often used, which improves the display quality of the quantized coarse image by adjusting or changing the amplitude value of the image.

Dithering can be achieved by adding a random small noise $d(x, y)$ to the original image $f(x, y)$. Since the value of $d(x, y)$ has no regular relationship with $f(x, y)$, it can help eliminate false contours in the image caused by insufficient quantization.

A specific method of dithering is as follows. Let $b$ be the number of bits in the image display, then the value of $d(x, y)$ can be obtained with uniform probability from the following 5 numbers: $-2^{(6-b)},-2^{(5-b)}, 0,-2^{(5-b)}$, and $2^{(6-b)}$. Adding the $b$ most significant bits of such a random small noise $d(x, y)$ to $f(x, y)$ provides the final output pixel values.

Figure $1.10$ shows a set of examples of dithering. Figure $1.10$ a is a part $(128 \times 128)$ of an original image with 256 gray levels (Figure 1.1a); Figure 1.10b shows the output effect of half-tone printing at the same size as the original image, by using the $3 \times 3$ half-tone mask. Since there are only 10 gray levels now, there are obvious false contour phenomena in regions where the gray-level change is relatively slow, such as the face and shoulders (the original continuously changing gray levels seem to have sharply changed gray levels now). Figure $1.10 \mathrm{c}$ is the result of adjusting the original image using dithering technology, and the superimposed dithering value is evenly distributed in the interval $[-8,8]$; Figure 1.10d shows the output effect of half-tone printing of the same size image after the dithering technology is used for improvement. The false contour phenomenon has been amended.

# 图像处理代考

1.1.4.1 半色调输出技术

## 有限元方法代写

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## MATLAB代写

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