英文:
Sobel filter - How to correctly display convolution result?
问题
I'm currently trying to implement my own version of the Sobel-Filter/Operator. I tried to pull as much information as possible from Wikipedia(https://en.wikipedia.org/wiki/Sobel_operator) and numerous explanations on YouTube, but I can't find a solution to my problem.
So after gray-scaling my image:
public BufferedImage grayscale(String path) {BufferedImage img = readImage(path);for (int x = 0; x < img.getWidth(); x++) {for (int y = 0; y < img.getHeight(); y++) {Color oldColor = new Color(img.getRGB(x, y));int red = oldColor.getRed();int green = oldColor.getGreen();int blue = oldColor.getBlue();int grayValue = (int) (0.244 * red + 0.587 * green + 0.114 * blue);Color newColor = new Color(grayValue, grayValue, grayValue);img.setRGB(x, y, newColor.getRGB());}}return img;}
I tried to extract the part of the image that should be convolved with the Sobel-Operator Sx. Since I gray-scaled the entire image, I figured it should be fine to use the red-portion since all values should be the same:
public void sobel(BufferedImage grayScaledImg) {for (int x = 1; x < grayScaledImg.getWidth() - 1; x++) {for (int y = 1; y < grayScaledImg.getHeight() - 1; y++) {int field1 = new Color(grayScaledImg.getRGB(x - 1, y - 1)).getRed();int field2 = new Color(grayScaledImg.getRGB(x, y - 1)).getRed();int field3 = new Color(grayScaledImg.getRGB(x + 1, y - 1)).getRed();int field4 = new Color(grayScaledImg.getRGB(x - 1, y)).getRed();int field5 = new Color(grayScaledImg.getRGB(x, y)).getRed();int field6 = new Color(grayScaledImg.getRGB(x + 1, y)).getRed();int field7 = new Color(grayScaledImg.getRGB(x - 1, y + 1)).getRed();int field8 = new Color(grayScaledImg.getRGB(x, y + 1)).getRed();int field9 = new Color(grayScaledImg.getRGB(x + 1, y + 1)).getRed();int[] currentPartOfImage = {field1, field2, field3, field4, field5, field6, field7, field8, field9};
And I'm pretty sure that in the following piece of code, I did something wrong but I can't figure out what:
int newGrayScale = sobelX(currentPartOfImage);grayScaledImg.setRGB(x, y, new Color(newGrayScale, newGrayScale, newGrayScale).getRGB());}}}
The sobelX-Function looks like this:
public int sobelX(int[] image) {return Math.abs(image[2] + (2 * image[5]) + image[8] - image[0] - (2 * image[3]) - image[6]);}
Problem: Some of the values I get while doing the convolution are larger than 255, which means they aren't valid RGB-values. So I'm currently not sure how to properly use those values?
Thanks in advance for the help! 
英文:
I'm currently trying to implement my own version of the Sobel-Filter/Operator. I tried to pull as much information as possible from Wikipedia(<https://en.wikipedia.org/wiki/Sobel_operator>) and numerous explanations on YouTube, but i can't find a solution to my problem.
So after gray-scaling my image:
public BufferedImage grayscale(String path) {BufferedImage img = readImage(path);for (int x = 0; x < img.getWidth(); x++) {for (int y = 0; y < img.getHeight(); y++) {Color oldColor = new Color(img.getRGB(x, y));int red = oldColor.getRed();int green = oldColor.getGreen();int blue = oldColor.getBlue();int grayValue = (int) (0.244 * red + 0.587 * green + 0.114 * blue);Color newColor = new Color(grayValue, grayValue, grayValue);img.setRGB(x, y, newColor.getRGB());}}return img;}
I tried to extract the part of the image that should be convolved with the Sobel-Operator Sx. Since i gray-scaled the entire image, i figured it should be fine to use the red-portion since all values should be the same:
public void sobel(BufferedImage grayScaledImg) {for (int x = 1; x < grayScaledImg.getWidth() - 1; x++) {for (int y = 1; y < grayScaledImg.getHeight() - 1; y++) {int field1 = new Color(grayScaledImg.getRGB(x - 1, y - 1)).getRed();int field2 = new Color(grayScaledImg.getRGB(x, y - 1)).getRed();int field3 = new Color(grayScaledImg.getRGB(x + 1, y - 1)).getRed();int field4 = new Color(grayScaledImg.getRGB(x - 1, y)).getRed();int field5 = new Color(grayScaledImg.getRGB(x, y)).getRed();int field6 = new Color(grayScaledImg.getRGB(x + 1, y)).getRed();int field7 = new Color(grayScaledImg.getRGB(x - 1, y + 1)).getRed();int field8 = new Color(grayScaledImg.getRGB(x, y + 1)).getRed();int field9 = new Color(grayScaledImg.getRGB(x + 1, y + 1)).getRed();int[] currentPartOfImage = {field1, field2, field3, field4, field5, field6, field7, field8, field9};
And i'm pretty sure that in the following piece of code i did something wrong but i cant figure out what..
int newGrayScale = sobelX(currentPartOfImage);grayScaledImg.setRGB(x, y, new Color(newGrayScale, newGrayScale, newGrayScale).getRGB());}}}
The sobelX-Function looks like this:
public int sobelX(int[] image) {return Math.abs(image[2] + (2 * image[5]) + image[8] - image[0] - (2 * image[3]) - image[6]);}
Problem <br />
Some of the values i get while doing the convolution are larger than 255, which means they aren't valid RGB-values. So i'm currently not sure how to properly use those values?
Thanks in advance for the help!
答案1
得分: 1
在执行卷积时，我得到的一些值大于255
通常可以通过使用"clamp"函数来解决这个问题。它是一个函数，用于检查参数是否在允许的范围内，如果不在范围内，则返回最接近的允许值。
int clamp(int value) {if (value > 255) return 255;if (value < 0) return 0;return value;}
这是如何使用它的方法：
int newGrayScale = clamp(sobelX(currentPartOfImage));
英文:
> Some of the values i get while doing the convolution are larger than 255
This is often solved by using a "clamp" function. It is a function that checks if the argument is in the allowed range, and if not, returns the closest allowed value.
int clamp(int value) {if (value > 255) return 255;if (value < 0) return 0;return value;}
And this is how you use it:
int newGrayScale = clamp(sobelX(currentPartOfImage));
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