Clarification of "% Crop"

[Jeff Dyck]

A clarification for me --> When folks on the site share a photograph and state this is a such-and-such "% crop" are they referring to the reduction in the area of the image or the length of a side?

Example - If a full frame image out of a camera is 6000x4000 pixels and the image is subsequently cropped down to 3000x2000 pixels what "% crop" would you consider that to be?

[Dan Brown]

Hi Jeff, there was a looooong thread regarding this sometime last year and I don't think a standard method was established? I refer to the rough % of the long edge of the original frame that I end up using. A simple method for a simple mind :bg3:

[Daniel Cadieux]

Here's that thread Dan talks about:

http://www.birdphotographers.net/forums/showthread.php/67504-How-Much-of-a-Crop-Part-II?highlight=crop

I'll use the same analogy as I did then, which Doug liked:t3: If I cut a lasagna in exactly half then eat one of the pieces...then I have only half left (50%). If I cut it in four equal parts and eat one piece, I have 3/4 left (75% of original). Some people prefer calculating the area, which gives a different result...but I'll stick to my method of calculating - makes me hungry!:S3:

[Jeff Dyck]

Thanks for the link Daniel - exactly the discussion I was looking for. I don't think there's actually a clear answer to the question in there, but it is apparent I am not the only one that is confused...

[Roger Clark]

Jeff,

I advocate not giving percent crop, but crop to X megapixels. For example, with a 1D Mark IV image, you can say: "I cropped to 12 megapixels" or "cropped from 16 to 12 megapixels." That is not ambiguous.

Roger

[WIlliam Maroldo]

I've gone round and round with this one, and I finally came to the same solution as Roger. As he stated, it is not ambiguous. It is easily checked in ACR (before and after the crop). regards~Bill

[Dave Leroy]

Thanks Bill.

I could not figure out to get the correct comparison. ACR was the answer.

Dave

[Dan Brown]

I've gone round and round with this one, and I finally came to the same solution as Roger. As he stated, it is not ambiguous. It is easily checked in ACR (before and after the crop). regards~BillAny recommendations for figuring the megapixel change if you don't use ACR? Is there a formula? I'm using Capture NX2, is there a way with this converter?

[William Malacarne]

Would it be possible to take the way that Roger suggested of doing this and present it to the powers that be and maybe post to the various forums so that every one will get on the same page.

Bill

[Doug Schurman]

The mega pixels should just be just simple arithmetic multiplying length by height in pixels right after making the crop?

For example, with the 7D the original file is 5,184 x 3,456 pixels. You multiply the two together and you get 17,915,904 or 17.9 megapixels (divide by 1 million). Let’s say you crop the image to 3,000 by 2,000 pixels. You now have a 6 megapixel image.

[John Chardine]

I think we are doomed to never solve this one here at BPN or anywhere!

I want something quick and easy so what I've been saying lately is "cropped to about x% of original size" based on a quick estimate of area of the cropped version compared to the original. So if the final processed image looked to be about 60% of the size (area) of the original I would say "cropped to about 60% of original size, i.e., 60% is left. I think this is the lasagne example of Daniel's. Anyway, this one makes sense to me.

[Ákos Lumnitzer]

What I use is a simple MS Excel formula. See attached image. I simply multiply width x height in both original resolution and cropped resolution fields, then the formula tells me the new size as a percentage of the original file. This particular example shows that the cropped image is exactly 58% of the original.

[Dan Brown]

What I use is a simple MS Excel formula. See attached image. I simply multiply width x height in both original resolution and cropped resolution fields, then the formula tells me the new size as a percentage of the original file. This particular example shows that the cropped image is exactly 58% of the original.Hey Akos, this is a great idea!

My opinion on the whole crop % issue is - that the crop question is "how much of full frame is this final image derivative?". For now I agree with John C. and Daniel C., an estimate of the % of the original frame is good enough.

So, if I am asked "how much did you crop this?" I can state "to about 60% of full frame" and this covers it. I don't have to reveal my original megapixel or do any math. If it becomes a requirement to state the exact crop, I would either us the ACR auto measurement or Mr. Lumnitzer's fine little Excel formula:S3:.