ComponentMeasurements[ _ ,"Centroid"] 结果偏移

发布于 2024-11-16 22:55:52 字数 1381 浏览 7 评论 0 原文

我需要获取一组具有亚像素精度的二进制图像中的组件的质心（质心）。

Mathematica 8 附带了一个很好的补充：

i =  Import@"https://i.sstatic.net/2pxrN.png";  
m1 = ComponentMeasurements[MorphologicalComponents[i], "Centroid"] /. 
                                                                Rule[_, x_] -> x
(*
-> {{403.229, 453.551}, {660.404, 371.383}, {114.389, 434.646}, {295.5, 206.}}
*)

但是当这些结果显示与其他地方完成的其他计算不一致时，我遇到了一些麻烦。

所以我推出了自己的，也许不太好：

i = Import@"https://i.sstatic.net/2pxrN.png";
f[i_] := N@{#[[2]], ImageDimensions[i][[2]] - #[[1]]} & /@
         ( Mean /@
             Function[x, Map[
                Position[x, #, 2] &,
                Complement[Union@Flatten[x], {0}]]]
             [MorphologicalComponents[i]]);
f[i]
Show[i, Graphics[{Red, Disk[#, 10] & /@ f[i]}]]
(*
-> {{403.729, 453.051}, {660.904, 370.883}, {114.889, 434.146}, {296., 205.5}}
*)

在此处输入图像描述

您可以看到这些之间有 0.5 的偏移量结果：

Thread[Subtract[m1, f[i]]]
(*
-> {{-0.5, -0.5, -0.5, -0.5}, {0.5, 0.5, 0.5, 0.5}}
*)

起初我以为问题与图像尺寸的偶数或奇数有关，但事实并非如此。

我更喜欢使用 ComponentMeasurements[ ..,"Centroid"] 并纠正结果，但我担心未来的 Mma 版本可能会修改此行为并破坏结果。

我还可以使用已知图像运行先前的“校准”并计算偏移，因此它会自动更正，但我想首先了解发生了什么。

这是一个错误吗？
关于为什么会发生这种情况有什么想法吗？

原文

I need to get the Center of Mass (Centroid) for components in a set of binary images with subpixel accuracy.

Mathematica 8 comes with a nice addition:

i =  Import@"https://i.sstatic.net/2pxrN.png";  
m1 = ComponentMeasurements[MorphologicalComponents[i], "Centroid"] /. 
                                                                Rule[_, x_] -> x
(*
-> {{403.229, 453.551}, {660.404, 371.383}, {114.389, 434.646}, {295.5, 206.}}
*)

But I went through some troubles when those results showed some inconsistencies with other calculations done elsewhere.

So I rolled my own, perhaps not nice:

i = Import@"https://i.sstatic.net/2pxrN.png";
f[i_] := N@{#[[2]], ImageDimensions[i][[2]] - #[[1]]} & /@
         ( Mean /@
             Function[x, Map[
                Position[x, #, 2] &,
                Complement[Union@Flatten[x], {0}]]]
             [MorphologicalComponents[i]]);
f[i]
Show[i, Graphics[{Red, Disk[#, 10] & /@ f[i]}]]
(*
-> {{403.729, 453.051}, {660.904, 370.883}, {114.889, 434.146}, {296., 205.5}}
*)

enter image description here

You can see that there is a .5 offset between these results:

Thread[Subtract[m1, f[i]]]
(*
-> {{-0.5, -0.5, -0.5, -0.5}, {0.5, 0.5, 0.5, 0.5}}
*)

At first I thought that the problem was related with the image dimensions being even or odd, but that is not the case.

I'd prefer using ComponentMeasurements[ ..,"Centroid"] and correcting the results, but I'm afraid future Mma versions may modify this behavior and spoil the results.

I could also run a previous "calibration" with a known image and calculate the offsets, so it will auto-correct, but I would like to understand what is going on first.

Is this a bug?
Any ideas about why is this happening?