Digital Software for counting pixels

[EEbal]

I need to be able to count the number of color pixels on an individual picture.   Specifically, my son's science project requires him to compare the effectiveness of cleaning white cloth samples.  I thought the best way to evaluate the results would be via a digital photo.  I would like to take a before and after photo of each sample, and obtain a digital summary of the white/black pixels.  The more white pixels, the cleaner the sample.  Does the Canon software allow you to see an overall summary of the digital photo sumarized in the overall number of black and white pixels?  If not, is there another suggestion that I could use to solve this problem?

[Waddizzle]

No, i would suggest an image editor, like MS Paint, which allow you to zoom in all the way down to the pixel level.

[EDIT]  A typical digital picture contains millions and millions of pixels.  I don't think you want to be counting and comparing pixels.  However, a histogram of the photo may be useful.

http://digital-photography-school.com/understanding-histograms/

The Canon DPP software does display low resolution histograms.  Whether or not the displays are accurate enough for your purposes is an entirely different matter.

[EEbal]

Acutally what I think I need is a delta number as I want to tabulate the relative difference between my before and after pictures of my sample. if the photo is monochrome, then the total number of black pixels to white would be useful.  this way I could measure the impact of the experiment.  do you know if the histrogram can tell me a total number of black and white pixels?

[Waddizzle]

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@EEbal wrote:

Acutally what I think I need is a delta number as I want to tabulate the relative difference between my before and after pictures of my sample. if the photo is monochrome, then the total number of black pixels to white would be useful.  this way I could measure the impact of the experiment.  do you know if the histrogram can tell me a total number of black and white pixels?

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If you make the images monochrome, then you will have to determine what shade of color/grey is the determining factor between black and white. Change the setpoint, and you may get very different results.

I think you're on the right track to reduce the number colors, but monochrome may be cutting it down too far.

The histograms that are available in most photo editors do not give you count of pixels, just a graph that indicates a percentage, which is not very accurate.  What you seek may require custom software. 

Then question to ask yourself is how accurate do I need to be?  Don't lose focus on the goal.  You were trying to determine whether or not a process makes a difference, not necessarily how much of a difference.  Right?

[EEbal]

that is correct.  Just trying to determine a relative difference and perhaps a percentage may be accurate enough.  I don't want to go to a customized software, just something good enough to give my a measurable indication.  So if the two histographs indicate a 1% difference in darker pixels, I would be able to report a result.  With that information, what software would you recommend?

[kvbarkley]

Just try every program you have that shows a histogram and choose the best one.

Do you have a PC or Mac?

[EEbal]

both a Mac and a PC

[kvbarkley]

I checked iPhoto and Photos, but their histograms are not very detailed.

Adobe Photoshop elements - and I assume photoshop - gives you a histogram that will let you view luminosity and show a lot of statistics and when you put the mouse over the histogram will show you the number of pixels in that "slice".

[kvbarkley]

It is not that simple. 255, 255, 255 is white. What about 250,250,250? or 256,256, 240?

You need pretty sophisticated software to do this. You might need photoshop, or even write your own.