[英]C++ Image Processing: Uniform Smoothing Operation Makes Image Darker
I'm trying to reduce noise in an image by creating a 2D uniform smoothing algorithm in C++. 我正在尝试通过在C ++中创建2D均匀平滑算法来减少图像中的噪声。 The function I'm using for each pixel computes the average value of neighboring pixels within a square odd window and uses that as the new value.
我为每个像素使用的函数计算平方奇数窗内相邻像素的平均值,并将其用作新值。
Whenever I run the code, however, the pixels in the new image become darker (a pixel value of 255=white, and 0=black). 但是,无论何时运行代码,新图像中的像素都会变暗(像素值255 =白色,0 =黑色)。 Here is the function for obtaining the new pixel value:
这是获取新像素值的函数:
int utility::windowAverage (image &src, int x, int y, int window_size)
{
int sum = 0;
int avg;
for(int i = x-(window_size/2); i < x+(window_size/2);++i)
{
for(int j = y-(window_size/2); j < y+(window_size/2);++j)
{
sum += src.getPixel(i,j);
}
}
avg = sum/(window_size*window_size);
return avg;
}
The parameter image &src
is the source image, and the function src.getPixel(i,j)
returns an integer from 0 to 255 representing the brightness of the pixel at the specified coordinates (i,j). 参数
image &src
是源图像,函数src.getPixel(i,j)
返回0到255之间的整数,表示指定坐标(i,j)处像素的亮度。
I am running the code over gray-level images of the .pgm format. 我正在.pgm格式的灰度图像上运行代码。
How can I smooth the image while maintaining the same brightness? 如何在保持相同亮度的同时平滑图像?
The problem is that you are not actually adding the pixels in a window with the dimension of windows_size*windows_size, but you are missing the last pixel in each dimension when computing sum
. 问题是您实际上没有在窗口尺寸为windows_size * windows_size的像素中添加像素,但是在计算
sum
时,每个尺寸的最后一个像素都丢失了。
You can fix this by using <=
instead of <
in both of your for loops. 您可以通过在两个for循环中使用
<=
代替<
来解决此问题。
Example of what is going wrong for window_size = 3
and x=0
and y=0
: window_size = 3
且x=0
和y=0
出问题的示例 :
The integer division by 2 in your for loops is floored, which means that your loops would become for (int i=-1; i < 1; i++)
. for循环中的整数除以2是有底数的,这意味着您的循环将变为
for (int i=-1; i < 1; i++)
。 This obviously only loops over the (two) pixles -1 and 0 in the given direction, but you still divide by the full window_size
of 3, which makes the image darker (in this case by one third if it has constant color values). 显然,这仅沿给定方向在(两个)像素-1和0上循环,但您仍需将
window_size
的完整值除以3,这会使图像更暗(在这种情况下,如果颜色值恒定,则为三分之一)。
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