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by Larry Shuman on Thu Feb 14, 2013 5:29 pm
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I've been digital since 2004. I shoot birds and crop most images, however I am not familiar with figuring out a crop percentage.
Is this a math excerise? If so I'm in deep trouble.

Thanks Much
Larry
 

by E.J. Peiker on Fri Feb 15, 2013 10:09 am
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Crop factor is simply the linear crop on a single side. So if you have an image that is 4000 pixels wide and you crop it down to 2000 pixels wide it is a crop factor of 2 or a linear reduction of 50%. Note that the area reduction is the square of the crop factor so when you do what I used as an example above, the area, or the remaining number of pixels is 1/4 of the original total so you are left with just 25% of the pixels. But the crop factor is the linear crop, not the area crop.

Lets say you have a 24 megapixel camera that puts out 6000x4000 pixel images. If you apply a crop factor of 2 (50% linear reduction) you are left with a 3000x2000 image which is only 6 megapixels. So the area reduction factor is 4 (75% area reduction or 25% area remaining) but the crop factor is 2. Hope that explains it :)
 

by LeOrmand on Fri Feb 15, 2013 11:35 am
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What EJ said makes my head hurt hah... on another nature photography website, I and other bird photographs subscribe to a simple standard to explain how much of an image is cropped.

You multiply the dimensions of the cropped image and then divide it by original dimensions. So, using EJ's numbers, you would simply multiply 3,000 X 2,000 which = 12,000,000 (pixels). Now you divide it by the number of pixels of your camera (say 24,000,000 or 24 MP). Again, this = 50%. I don't see a reason to talk about a "crop factor" or to discuss the number of pixels remaining though it is relevant to include the # of pixels your camera has.

Hmm... not sure this is any more simple than EJ's above!
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by Larry Shuman on Fri Feb 15, 2013 12:36 pm
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My image is 4556 X 2832. The camera is Nikon D3. The file size is 14.56MP because I've set the
camera to 14bit.
So 4556 X 2832 = 129,025,592 and divide that by 12,000,000 = 1.07
My cropped dim is 1800 X 1200
I still do not understand.

Thanks
Larry
 

by J. DeYoung on Fri Feb 15, 2013 12:57 pm
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Larry, I believe that would be 16.7%

Your original file size is 4556x2832 or 12,902,592 megapixels (The bit depth doesn't matter)
Your cropped file size is 1800x1200 or 2,160,000 megapixels

Divide the cropped file size by the original file size.
2,160,000 / 12,902,592 = 0.167

Then Multiply that number by 100 to get the percent.
0.167 * 100 = 16.7%
 

by E.J. Peiker on Fri Feb 15, 2013 1:04 pm
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LeOrmand wrote:What EJ said makes my head hurt hah... on another nature photography website, I and other bird photographs subscribe to a simple standard to explain how much of an image is cropped.

You multiply the dimensions of the cropped image and then divide it by original dimensions.  So, using EJ's numbers, you would simply multiply 3,000 X 2,000 which = 12,000,000 (pixels).  Now you divide it by the number of pixels of your camera (say 24,000,000 or 24 MP).  Again, this = 50%.  I don't see a reason to talk about a "crop factor" or to discuss the number of pixels remaining though it is relevant to include the # of pixels your camera has.

Hmm... not sure this is any more simple than EJ's above!
Um no ;)  The last time I checked 3x2=6 not 12 :D
 

by E.J. Peiker on Fri Feb 15, 2013 1:14 pm
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Larry Shumanlbs wrote:My image is 4556 X 2832. The camera is Nikon D3. The file size is 14.56MP because I've set the
camera to 14bit.
So 4556 X 2832 =  129,025,592 and divide that by 12,000,000 = 1.07
My cropped dim is 1800 X 1200
I still do not understand.

Thanks
Larry
No, that isn't how you calculate crop percentage, that is how you calculate area percentage.

The simple explanation: If you go from 4556 wide to 1800 wide you now have  39.5% of the width that you had so your crop factor is 1/0.395 or 2.53.

The full explanation:
Your math is wrong :)

First off 4556x2832= 12,902,592 - you have an extra 5 in there.
1800x1200=2160,000

So you are left with 16.7% of the original pixels.  Your area reduction is from 100% to 16.7% but this is NOT crop factor.  That is area reduction.  Your area percentage of the original image which is the same as the pixel percentage of the original image is 16.7%.

Your crop which is measured along a linear side is 39.5% of the original (1800/4556=0.395 or 39.5%)
 

by Larry Shuman on Fri Feb 15, 2013 1:36 pm
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Many thanks EJ. It all makes sense now.
I have never been good at math.

Larry
 

by Randy Mehoves on Sat Feb 16, 2013 11:29 am
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Dang, almost all the answers make it very confusing, even if you know how!
Simple answer is:
crop pixels (length x width) divided by camera native size (length x width)= percentage of original image size. (after moving decimal point to the right 2 places)
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by E.J. Peiker on Sat Feb 16, 2013 11:55 am
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Randy Mehoves wrote:Dang, almost all the answers make it very confusing, even if you know how!
Simple answer is:
crop pixels (length x width) divided by camera native size (length x width)= percentage of original image size. (after moving decimal point to the right 2 places)
Yes but that wasn't the question!  The question was crop percentage, not area percentage ;)  Crop is measured on a single axis, area is the product of both axis.

Otherwise something like the 1.5x DX crop would be 2.25 which is the area reduction but not the crop factor.  Nothing confusing about it at all :mrgreen:
 

by LeOrmand on Sat Feb 16, 2013 12:00 pm
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E.J. Peiker wrote:
LeOrmand wrote:What EJ said makes my head hurt hah... on another nature photography website, I and other bird photographs subscribe to a simple standard to explain how much of an image is cropped.

You multiply the dimensions of the cropped image and then divide it by original dimensions.  So, using EJ's numbers, you would simply multiply 3,000 X 2,000 which = 12,000,000 (pixels).  Now you divide it by the number of pixels of your camera (say 24,000,000 or 24 MP).  Again, this = 50%.  I don't see a reason to talk about a "crop factor" or to discuss the number of pixels remaining though it is relevant to include the # of pixels your camera has.

Hmm... not sure this is any more simple than EJ's above!
Um no ;)  The last time I checked 3x2=6 not 12 :D
Must have forgot to carry the one!  Thanks EJ!
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by Randy Mehoves on Sat Feb 16, 2013 7:55 pm
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E.J. Peiker wrote:
Randy Mehoves wrote:Dang, almost all the answers make it very confusing, even if you know how!
Simple answer is:
crop pixels (length x width) divided by camera native size (length x width)= percentage of original image size. (after moving decimal point to the right 2 places)
Yes but that wasn't the question!  The question was crop percentage, not area percentage ;)  Crop is measured on a single axis, area is the product of both axis.

Otherwise something like the 1.5x DX crop would be 2.25 which is the area reduction but not the crop factor.  Nothing confusing about it at all :mrgreen:
I wish the OP would chime in because I believe 9 times out of 10 the term "crop percentage" gets used when what is really meant is how much of the original image remains after the crop. Plus I think it's much easier for the average person to comprehend the area left rather than trying to discern the camera model so they can figure crop factor and then how much was actually cropped away.
Maybe that's just the way I think..........LOL.
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by E.J. Peiker on Sun Feb 17, 2013 12:14 am
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He did chime in and said that he understands now ;)
 

by Steve Cirone on Tue May 14, 2013 7:51 am
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Does the percentage even matter?

When desperate, I crop until the image falls apart, then I know I went too crazy.

Best to shoot as full frame as possible. Gotta love all those pixels. For super crop freaks, nothing beats the new Nikon D 800 at 36 megs. You can buzz saw those images to death and still have a nice image left. Within reason of course.
 
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by dbostedo on Tue May 14, 2013 3:00 pm
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While this seems to be taken care of for the OP, I'd prefer (and I think it's easy) if someone says that the image posted is x% of the original area/pixels. So if you started with 20MP and your image is cropped to 10MP, it would be a 50% crop.

I know that doesn't match with the crop-factor used for sensors, which is clearly linear, not area based. But it seems more intuitive to me. Maybe I just think in 2D. (Or symantically, to me, a "50% crop" sounds like it should refer to area.)
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