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compute mean and standard deviation of RGB color

Posted on 1998-04-15
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Last Modified: 2008-03-17
Hello..., I really need your help..URGENT..and please reply as soon as
possible. I was given a few sample of images in BMP format (device-
independent-bitmap(DIB). Can you give me a few sample of the source code
on how to compute the mean and the standard deviation on the RGB color
for each sample to take the average color to get the standard color of the
image( for example I took 10 sample of images of pepper berries). Thanx.
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Question by:juexxs
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4 Comments
 
LVL 11

Expert Comment

by:alexo
ID: 1184303
Sounds like homework...
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Expert Comment

by:nietod
ID: 1184304
I'm not sure.  That sounds too weird to be even homework.  

There is a lot involved in this process.  Can you tell us what you problem areas are?  also if it is homework, we will still be happy to HELP you, but we won't do it for you.  For (100 points on a question of this size, no one is likely to do it for you in any case).
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LVL 10

Accepted Solution

by:
RONSLOW earned 60 total points
ID: 1184305
Should be fairly simple..

Load the bitmap file into a HBITMAP object in memory

Once you have the bitmap object, associate a device context with it (CreateCompatibleDC and select the bitmap into it).

You can get the RGB (COLORREF) data at any pixel with GetPixel()

Write nexted for loops that go through the entire bitmap and accumulate and count the rgb components of each pixel.  Then do the statistics

An alternative is to use some of the OpenGL code which reads in bitmap files and stores them in an array of RGB values.  Then you can just do some array arithmetic

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Expert Comment

by:RONSLOW
ID: 1184306
Here is some code using OpenGL functions to read in the bitmap from a file and compute the average colour

#include <glu.h>
#include <GLAUX.H>

COLORREF AverageColor (LPCTSTR filename) {
  AUX_RGBImageRec *pImage;

  glPixelStorei(GL_PACK_ALIGNMENT, 1);
  glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

  pImage = ::auxDIBImageLoad(filename);

  int sum[3] = {0,0,0};
  int ave[3];

  int n = pImage->sizeX*pImage->sizeY;
  for (int i = 0; i < n*3; i+=3) {
    sum[0] += pImage->data[i+0];
    sum[1] += pImage->data[i+1];
    sum[2] += pImage->data[i+2];
  }
  ave[0] = unsigned char (sum[0]/n);
  ave[1] = unsigned char (sum[1]/n);
  ave[2] = unsigned char (sum[2]/n);

  return RGB(ave[0],ave[1],ave[2]);
}

You can expand this to do std dev etc.

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