How do I draw the cumulative histogram curve in c# ,.net?

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Hi,
I managed to draw the histogram by referring the following link
http://trompelecode.com/blog/2012/04/how-to-create-an-image-histogram-using-csharp-and-wpf/

I drawn input histogram and output histogram i.e after performing the image enhancement operations

Now I want to plot cumulative histogram curve showing the difference in original image pixel and change in pixel after
adjustments like image enhancement operations...

I am referrring following link
http://azzlsoft.com/tag/histogram-equalization/ link

facing problem in the follow code snippet

for (int pixelIndex = 0;
pixelIndex < grayscale.Pixels.Length;
pixelIndex++)
{
byte intensity = (byte)(grayscale.Pixels[pixelIndex] & 0xFF) ;
histogramData[intensity]++;
}
I am not getting the intensity value as writablebitmap grayscale not finding .Pixels[pixelIndex] methode

thanks in advance.... Smile | :)

Posted 9-Sep-14 22:17pm

vdeo1

Updated 10-Sep-14 23:16pm

v3

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Comments

George Jonsson 10-Sep-14 4:54am

Is your problem to calculate or to draw the cumulative histogram?

vdeo1 10-Sep-14 8:16am

calulate the value of cumulative graph..

Member 13341679 29-Sep-17 6:50am

Hi vdeo1, can you please give me the codes to draw the histogram of a bitmap image ?
mail: shubhakantas@gmail.com

2 solutions

Solution 1

Well, if you are working on an image the intensity values for the pixels will have a certain frequency.
10 pixels will have the intensity value of 0, 25 pixels the value of 1, etc.
The cumulative frequency is the sum of the previous frequencies including the current intensity

So you will have a table like this:

Intensity	Frequency	Cumulative Frequency	Calculation
0	10	10	0 + 10
1	25	35	10 + 25
2	30	65	35 + 30
3	35	100	65 + 35
4	30	130	100 + 30
etc.

Posted 10-Sep-14 15:03pm

George Jonsson

Comments

vdeo1 11-Sep-14 2:50am

On which parameters the frequency is defined/decided or we take the frequency randomly??
I just gone through the follw link
http://azzlsoft.com/tag/histogram-equalization/

But I am not getting grayscale.Pixels[pixelIndex] so cant getting the intensity

George Jonsson 11-Sep-14 2:57am

Ehrm, you state in your question that you already have the histogram.
Hence, I showed how to calculate the cumulative frequency from an existing histogram.
What have you done so far?

vdeo1 11-Sep-14 4:27am

I managed to get the histogram by referring the following link
http://trompelecode.com/blog/2012/04/how-to-create-an-image-histogram-using-csharp-and-wpf/

I drawn input histogram and output histogram i.e after performing the image enhancement operations
Now I want to plot curve showing the difference in original image pixel and change in pixel after adjustments like image enhancement operations...

George Jonsson 11-Sep-14 4:35am

So in what part of your code are you stuck?

vdeo1 11-Sep-14 4:43am

On http://azzlsoft.com/tag/histogram-equalization/ link

for (int pixelIndex = 0;
pixelIndex < grayscale.Pixels.Length;
pixelIndex++)
{
byte intensity = (byte)(grayscale.Pixels[pixelIndex] & 0xFF) ;
histogramData[intensity]++;
}
I am not getting the intensity value as writablebitmap grayscale not finding .Pixels[pixelIndex] methode

George Jonsson 11-Sep-14 5:08am

Update your question with this code. Use 'Improve question' above.

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vdeo1 · Accepted Answer · 2014-09-22T00:35:00

int[] histogramData = new int[256];
WriteableBitmap writeableBmp;
System.Drawing.Bitmap bitmap;
using (MemoryStream outStream = new MemoryStream())
{
writeableBmp = new writeableBitmap(System.Windows.Interop.Imaging.CreateBitmapSourceFromHBitmap(img.GetHbitmap(),IntPtr.Zero,Int32Rect.Empty,BitmapSizeOptions.FromEmptyOptions()));
}

int[] a = new int[img.Width * img.Height];
for (int pixelIndex = 1; pixelIndex < 256; pixelIndex++)
{
writeableBmp.CopyPixels(a, 1680, pixelIndex);
}

for (int pixelIndex = 1; pixelIndex < img.Width * img.Height; pixelIndex++)
{

byte intensity = (byte)(a.ElementAt(pixelIndex) & 0xFF);
histogramData[intensity]++;
}

for (int intensity = 1; intensity < 256; intensity++)
{
//now we just add the current probability
//to the previous CDF
cumulativeDistributionFunction[intensity] = ((histogramData[intensity]) / img.Width * img.Height) + cumulativeDistributionFunction[intensity - 1];
}
//curve = cumulativeDistributionFunction;
curve = ConvertToPointCollection(cumulativeDistributionFunction);