Opencv4nodejs: [ Request ] compareHist sample code

[bgsuello]

hi,

can I request a sample code for comparing histogram of two different image?

thanks,

[justadudewhohacks]

Hi,

There is an example how to create and plot histograms:
https://github.com/justadudewhohacks/opencv4nodejs/blob/master/examples/plotHist.js

Comparing histograms is done by const val = hist1.compareHist(hist2, method), where method is one of the OpenCV codes for the comparison methods.

I am not quite sure, but I think at the moment opencv4nodejs can only handle up to 3 dimensional histograms.

[bgsuello]

If that is the case then i'm doing it right, but in electronjs, when I try to compare histogram the renderer process is crashing(white screen) although I successfully plot H1 and H2 using your example code, just the part with H1.compareHist(H2, cv.HISTCMP_CORREL) keeps crashing.

let mat1 = cv.imread('image1.jpg')
const H1= this.calcHist(mat1) // this will return 3d histogram
let mat2 = cv.imread('image2.jpg')
const H2 =this.calcHist(mat2) 

const result = H1.compareHist(H2, cv.HISTCMP_CORREL) // this line keeps on crashing

i'm on windows 10, using opencv 3.4.

Any idea why is this happening?

[justadudewhohacks]

Crashing without any error message or stacktrace? You can check segfaults via npm segfault handle. But it doesnt work with multithreaded code

[bgsuello]

_Crashing without any error message or stacktrace?_ __YES__

i will try that, thanks a lot.

[bgsuello]

So I was able to make it work.
Thanks a lot for awesome work @justadudewhohacks 👍

const cv = require('../');

let baseImg = cv.imread('../data/ph-1.jpg').convertTo(cv.CV_32F);
let sampleImg= cv.imread('../data/Lenna.png').convertTo(cv.CV_32F);

let baseHist = cv.calcHist(baseImg, [{channel: 1, ranges: [0, 255], bins: 255}]).convertTo(cv.CV_32F)
let sampleHist = cv.calcHist(sampleImg, [{channel: 1, ranges: [0, 255], bins: 255}]).convertTo(cv.CV_32F)

console.log(sampleHist.compareHist(baseHist, cv.HISTCMP_CORREL)) // 0.03410325814186557

[justadudewhohacks]

Great!