How to get the histogram's Std Dev

[raxby]

  getRedHistogramStdDev(); 

  function getRedHistogramStdDev() {

      var channels = app.activeDocument.channels;

      var red = channels[0].histogram;

      alert(getStdDev(red));

  }

function getStdDev(arry){

        var length = arry.length; 

        var tarry = new Array(length);

        var si = 0;

        var s = 0;

        for (var i = 0; i < arry.length; i += 1) {

            if (arry[i] > 0) {

                s += i;

                si += arry[i];

            }

        }

        var average = si / s;

        for (var i = 0; i < length; i++) {

            var dev = parseFloat(arry[i]) - parseFloat(average);

            tarry = Math.pow(dev, 2);  

        }

        var powSum = 0;

        for (var j = 0; j < tarry.length; j++) {

            if (tarry[j].toString() != "" || tarry[j].toString() != null) {

                powSum = parseFloat(powSum) + parseFloat(tarry[j].toString()); 

            }

        }

        return Math.sqrt(parseFloat(powSum) / parseFloat(length)).toFixed(2);

}

This is my code, but the result is inconsistent with the histogram's StdDev data.Please help me, thanks.

[c.pfaffenbichler · Accepted solution]

Does this work more consistently? 

// 2018, use at your own risk;

#target "photoshop-120.032"

//#target photoshop

if (app.documents.length > 0 && activeDocument.mode == DocumentMode.RGB) {

var theR = histogramMeanStandardDeviation(activeDocument.channels[0].histogram);

var theG = histogramMeanStandardDeviation(activeDocument.channels[1].histogram);

var theB = histogramMeanStandardDeviation(activeDocument.channels[2].histogram);

alert ((theR[2]+theG[2]+theB[2])/3);

};

////// get mean of histogram //////

function histogramMeanStandardDeviation (theHist) {

// get total number;

var thePixels = 0;

for (var m = 0; m < theHist.length; m++) {

  thePixels = thePixels + theHist[m]

  };

// get mean and median;

var theMean = 0;

var aTotal = 0;

var check = false;

for (var n = 0; n < theHist.length; n++) {

  theMean = theMean + (n * theHist[n] / thePixels);

  aTotal = aTotal + theHist[n];

  if (aTotal >= thePixels / 2 && check == false) {

  theMedian = n;

  check = true;

  }

  };

// get standard deviation;

var theStandDev = 0;

for (var o = 0; o < theHist.length; o++) {

  theStandDev = theStandDev + (Math.pow ((o - theMean), 2) * theHist[o])

  };

theStandDev = Math.sqrt (theStandDev / thePixels);

//

return ([theMean, theMedian, theStandDev]);

};

[raxby]

Yes,It works very well,thank you very much！

[raxby]

Hi c.pfaffenbichler,sorry to disturb you.I want to get value of theMax and theMin in histogram not the the pixels,how to get this? Thanks

[c.pfaffenbichler]

Does this work? (Edit: Otherwise I may have misunderstood your intention.)

// 2018, use at your own risk;

#target "photoshop-120.032"

//#target photoshop

if (app.documents.length > 0 && activeDocument.mode == DocumentMode.RGB) {

var theMinMax = histogramMinMax(activeDocument.histogram);

alert ("min "+theMinMax[0]+"\nmax "+theMinMax[1]);

};

////// get mean of histogram //////

function histogramMinMax (theHist) {

// the minimum;

var check = false;

var theMin = 0;

while (check == false) {

if (theHist[theMin] != 0) {

check = true

} else {theMin++}

};

// the maximum;

var check = false;

var theMax = 255;

while (check == false) {

if (theHist[theMax] != 0) {

check = true

} else {theMax--}

};

//

return ([theMin, theMax]);

};

[raxby]

It is that i mean, forgive me for not being clear,because i am not clear about the relationship with them which like "n * theHist" in histogram.Thanks again.

[c.pfaffenbichler]

n being the index also indicated the luminance while theHist indicates the number of pixels of that luminance.

[Kukurykus]

You got almost full stake! Last time I looked at, you was at 8 lvl. It'll take another century your skull will be finally inpaled 🙂

[c.pfaffenbichler]

I think the last »bar« of those levels takes a lot of points, no hurry …

[raxby]

Ok,thanks

[Kukurykus]

I got it. I have ling54k in list of users I follow, actually he added me first. It's why I was announced of his topic.

[rechmbrs]

Will this work on 32 bpc floating point data?  If not, is there a quick workaround?

Thanks,

RONC

[rechmbrs]

It does work on 32 bpc data very well.  Just need to display the histograms.

RONC

[Kukurykus]

That's 3rd topic during last month I'm called constantly to although neither I haven't posted anything on here nor anyone mentioned my forum name 😕 That must be some error 😕

[c.pfaffenbichler]

Well, would not be the first time the Forum software displays »issues«, would it?

Have you tried contacting an Admin or asking about the issue on

Forum comments

yet?

[Kukurykus]

No that is no problem for me, it doesn't happen often, especially taking into consideration I forgot 's' at end of 'month' in last post. So once a 1,5 month something causing I'm alerted of new posts in certain topic.

[Rudolf L]

Hello dearest people and @c.pfaffenbichler !

I don't get this script working. Gives me a spinning cursor and after that nothing happens. Then i fired it in ESTK and it gave me "theMedian is undefined". I tried to figure it out by myself but the best what i get out of it is "NaN" lol.
Is this again some typo error because of the glorious change of forum software? If yes, i don´t find it,

The first script from @raxby gives me "0.00" all the time btw.
Thanks for your help in advance!

[Stephen_A_Marsh]

I can also add that I can't get the script working in later versions either, looking for the Std Dev.

[Kukurykus]

I corrected the scripts.

[Stephen_A_Marsh]

@Kukurykus  – thank you!