Negative mean from ImageStatistics?

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RandoJones

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Jan 14, 2021, 5:22:41 PM1/14/21
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Hey all,

Would you expect a negative mean from an image whose smallest value is 0?

BufferedImage bi =imp.getStack().getProcessor(m).convertToShortProcessor().get16BitBufferedImage();
System.out.println("Stats: "+imp.getStack().getProcessor(m).convertToShortProcessor().getStatistics() );
        
Stats: stats[count=2114116, mean=1775.7265202098654, min=0.0, max=65535.0]  //ok
...
GrayU16 input16 = ConvertBufferedImage.convertFromSingle(bi,null,GrayU16.class);
System.out.println("Mean of input image: " +ImageStatistics.mean(input) );
System.out.println("Max of input image: " +ImageStatistics.max(input) );
System.out.println("Min of input image: " +ImageStatistics.min(input) );

Mean of input image: -255.84000499499555.  //???
Max of input image: 65535
Min of input image: 0

I also scanned through the pixels manually and did not detect any negative values.

Thanks in advance.

RandoJones

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Jan 14, 2021, 5:25:13 PM1/14/21
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input = input16...typo.  

RandoJones

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Jan 14, 2021, 5:26:15 PM1/14/21
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Question still relevant.

Peter A

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Jan 14, 2021, 6:56:02 PM1/14/21
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I'll double check, but I'm betting the integer overflowed as it was summing. Might need to add a "safe" variant which is slower but much harder to overflow.

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RandoJones

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Jan 15, 2021, 11:51:32 AM1/15/21
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Thanks for looking into it!

For some additional information:  I attempted to compute the image mean manually.  Retrieving the individual pixel values using the get() accessor:

...
int v = subInput.get(i,j);
sum = sum + v;
...

Sum:   -1210085007

---

If I retrieve them as double or long, I get a positive result.

Thanks!
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