regionprops and standard deviation (binary image)

2018 1 26
2 个回答
回答已采纳
更新时间：2018 1 31
4 次查看（30 天）

0 个投票

Hi everyone, i am using the function" regionprops" to get the largest perimeter in my binary image. I have got the value of the largest perimeter but still need to have its standard deviation. Does anyone know how to get this std? Thank you very much

请先登录，再回答此问题。

 采纳的回答

Walter Roberson
Walter Roberson 2018-1-26

0 个投票

When you do the regionprops() also ask for 'PixelIdxList' . When you find the region with the largest perimeter, extract its PixelIdxList. Use that PixelIdxList to index the 2D image, and take std() of the pixels that are returned.
If your original image was color, then sometimes the easiest is to break it into 3 variables and use PixelIdxList on each. That is not the only way, but it is easy to understand whereas the conversion of 2D linear indices to appropriate 3D indices can be a bit tricky to understand.

5 个评论
显示 3更早的评论 隐藏 3更早的评论

marie semaan
marie semaan 2018-1-29
编辑：Walter Roberson 2018-1-29
I appreciate your help in this matter.
I have written the following code:
s = regionprops(binaryimage,'PixelIdxList','Perimeter')% original image is not a color image
allPerimeters =[s.Perimeter]% all perimeters in this binary image
largestPerimeterIs=allPerimeters(1); % the largest perimeter value is the first value in allPerimeters
for k = 1:NumObjects
s(k).RegionNumber = mode(single(originalImage(s(k).PixelIdxList(1))));
end
region_vector = [s.RegionNumber]
How can i extract the PixelIdxList of the region with the largest perimeter in order to apply the std of all those returned pixels?
Thank you again
Walter Roberson
Walter Roberson 2018-1-29
originalImage(s(k).PixelIdxList(1)) is going to be a scalar value, so I do not understand why you would mode() it?
"How can i extract the PixelIdxList of the region with the largest perimeter"
[~, objidx] = max(allPerimeters);
std( double(OriginalImage(s(objidx).PixelIdxList)) )
marie semaan
marie semaan 2018-1-29
编辑：Walter Roberson 2018-1-29
by trying the following code, std is equal to 0. What shall i change in the "std(double(OriginalImage(s(objidx).PixelIdxList)))"?
s = regionprops(binaryimage,'all')
[~, objidx] = max(allPerimeters);
std(double(OriginalImage(s(objidx).PixelIdxList)))
thank you
Walter Roberson
Walter Roberson 2018-1-29
s = regionprops(binaryimage,'all')
[~, objidx] = max(allPerimeters);
obj_pixels = OriginalImage(s(objidx).PixelIdxList);
if length(unique(obj_pixels)) == 1
sprintf('all pixels in the object are exactly the same! All of them have value %d\n', obj_pixels(1));
else
std(double(obj_pixels))
end
Depending how your image was constructed and how you are constructing your binary image, the situation could either be an improbable coincidence or something to be expected. You could post your image and your code that creates the binary image for us to examine.

请先登录，再进行评论。

更多回答（1 个）

Image Analyst
Image Analyst 2018-1-30

0 个投票

You can get the standard deviation of the gray levels in the blob with the largest perimeter more directly (than by using PixelIdxList) like this:
% Get blob with largest perimeter.
binaryImage = bwpropfilt(binaryImage, 'Perimeter', 1);
% Get standard deviation of pixels in that blob
stdGrayLevels = std(double(grayImage(binaryImage)))

1 个评论
显示 -1更早的评论 隐藏 -1更早的评论

marie semaan
marie semaan 2018-1-31
Thank you for your help. I prefer to use the above code in my case. i have tried your code but it did not work.

请先登录，再进行评论。

类别

在 帮助中心 和 File Exchange 中查找有关 Region and Image Properties 的更多信息

产品

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by