Area Calculation in binary image
显示 更早的评论
I have to calculate the area of an object in binary image. i have used "nnz" for this but it gives result in number of pixels, hw can i convert it to area unit? I want the result in mm, during searching I have found that resolution or dpi can be used for this. But am confused about coding
o=nnz(bw3)
dpi = get(0, 'ScreenPixelsPerInch');
inches = o ./ dpi;
mm = inches * 2.54;
Is that correct?
回答（1 个）
Image Analyst
2012-7-26
编辑：Image Analyst
2012-7-26
1 个投票
What are your units? Square centimeters? Square kilometers? A pixel image does not know. You have to specify the spatial calibration. Do you know the size of your field of view, or of any object in your image, in real world units?
Regarding your update. No that's not correct. That will get you distance on the screen in cm, not mm (because there is 25.4 mm in an inch, not 2.54), and certainly not area in mm^2. You'd have to multiply by 25.4^2. Plus, o is a horrible letter to pick for a variable name - it looks too much like zero.
Do you want the real world area of your actual object that you took a picture of, or do you want the area that it takes up on your screen monitor?
2 个评论
Sehrish
2012-7-27
gargoyle
2012-8-2
Assuming that you want to measure an object which you took a picture of:
While acquiring your image you will need something of a known distance to set your scale with. Using this as a ruler you can determine (manually) the number of pixels per unit distance. once you know that, and assuming that all your images are taken at under the same conditions, you can apply the pixels to distance conversion. If all your images are not taken under the same conditions you will need that ruler for every image.
类别
在 帮助中心 和 File Exchange 中查找有关 Image Arithmetic 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
