实施laplacian 3x3 [英] implement laplacian 3x3
问题描述
我读过Gonzalez和Woods的DIP第二版,并使用wxImage尝试使用拉普拉斯面具(第129和130页)。
Im reading DIP 2nd edition by Gonzalez and Woods and try to my hands dirty with Laplacian mask (page 129&130) using wxImage.
float kernel [3][3]= {{1, 1, 1},{1,-8, 1},{1, 1, 1}};
这里是处理循环:
unsigned char r,g,b;
float rtotal, gtotal, btotal; rtotal = gtotal = btotal = 0.0;
//ignore the border pixel
for(int i = 1; i<imgWidth-1; i++)
{
for(int j = 1; j<imgHeight-1; j++)
{
rtotal = gtotal=btotal =0.0;
for(int y = -1; y<=1;y++)
{
for(int x = -1; x<=1;x++)
{
// get each channel pixel value
r = Image->GetRed(i+y,j+x);
g = Image->GetGreen(i+y,j+x);
b = Image->GetBlue(i+y,j+x);
// calculate each channel surrouding neighbour pixel value base
rtotal += r* kernel[y+1][x+1];
gtotal += g* kernel[y+1][x+1] ;
btotal += b* kernel[y+1][x+1];
}
}
//edit1: here is how to sharpen the image
// original pixel - (0.2 * the sum of pixel neighbour)
rtotal = loadedImage->GetRed(x,y) - 0.2*rtotal;
gtotal = loadedImage->GetGreen(x,y) - 0.2*gtotal;
btotal = loadedImage->GetBlue(x,y) - 0.2*btotal;
// range checking
if (rtotal >255) rtotal = 255;
else if (rtotal <0) rtotal = 0;
if(btotal>255) btotal = 255;
else if(btotal < 0) btotal = 0;
if(gtotal > 255) gtotal = 255;
else if (gtotal < 0 ) gtotal =0;
// commit new pixel value
Image->SetRGB(i,j, rtotal, gtotal, btotal);
我把它应用到北极图片(灰色图片),我得到的是一个黑点和白色像素!
I applied that to the North Pole picture (grey image) and all I get is a blob of black and white pixels!
任何想法我可能错过了在for循环中的一些东西?
Any ideas where may I have missed something in the for loops?
Edit1:得到的答案后,在谷歌翻阅。这个dsp东西是绝对棘手!我添加到上面的代码,它将锐化图像。
Finally get the answer after looking around on google. This dsp stuff is definitely tricky! I added to the code above, it will sharpen the image.
干杯
推荐答案
首先,与拉普拉斯卷积的结果可以具有负值。考虑由0包围的值为1的像素。在该像素处的卷积的结果将是-8。
First, the result of convolving with a Laplacian can have negative values. Consider a pixel with a value of 1 surrounded by 0's. The result of the convolution at that pixel will be -8.
其次,结果的范围将在[-8 * 255,8 * 255]之间,这绝对不适合8位。基本上,当您进行范围检查时,您将丢失大部分信息,并且大部分生成的像素将最终为0或255.
Second, the range of the result will be between [-8 * 255, 8 * 255], which definitely does not fit into 8 bits. Essentially, when you do your range checking, you are losing most of the information, and most of your resulting pixels will end up either being 0 or 255.
您有什么要做的是将结果存储在一个类型的数组,该数组是有符号的,足够宽以处理该范围。然后,如果要输出8位图像,则需要重新调整值,以便-8 * 255映射为0,并且8 * 255映射为255.或者,您可以重新缩放,以使最小值映射到0和最大值映射到255.
What you have to do is store the result in an array of a type that is signed and wide enough to handle the range. Then, if you wish to output an 8-bit image, you would need to rescale the values so that -8 * 255 maps to 0, and 8 * 255 maps to 255. Or you can rescale it so that the least value maps to 0 and the greatest value maps to 255.
编辑:在此特定情况下,您可以执行以下操作:
in this specific case, you can do the following:
rtotal = (rtotal + 8 * 255) / (16 * 255) * 255;
这简化为
rtotal = (rtotal + 8 * 255) / 16;
这会将rtotal映射到0到255之间的范围,而不会截断。您应该对 gtotal
和 btotal
执行相同操作。
This would map rtotal into a range between 0 and 255 without truncation. You should do the same for gtotal
and btotal
.
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