Rich Ditch's Photography Blog

March 24, 2009

Crop Percentages

Filed under: Birds, composition, favorite places, technique, Veterans Oasis Park — richditch @ 4:54 pm
Crop Percentage Examples

Crop Percentage Examples

Cropping an image is a fact of life for many of us that work with real subjects in the real world and don’t have the advantages of total control over subjects that move around on their own. I prefer to “shoot lose” when I’m working so I don’t amputate part of my subject with too tight framing; cropping the image in final post processing lets me fine tune the composition for the proper balance between subject and setting that suits my goals.

But from years of posting and critiquing images on various photography sites on the internet I’ve come to see how many people struggle with calculating how much they crop an image, and I’ve taken the time to write down the basics so it is always available for quick reference on my web site.

Calculating Crop Percentages

I feel it is important to disclose how much an image has been cropped if it is posted on a photo critique site where learning and information sharing are primary goals. Disclosing that a posted image is a substantial crop is simply honesty about how close the photographer actually got to the subject; keeping quiet about such a large crop is dishonest and misleads viewers about the photographer’s skills and sets up unreasonable expectations for beginning photographers who haven’t mastered field techniques on getting close.

But there’s no obvious standard way to specify how much an image has been cropped, and a lot of inaccurate and confusing comments are made trying to indicate this. To me, it’s simple: express pixels remaining after the crop as a percentage of the pixels before the crop. Let’s take a 6MP original and crop it as an example:

Original: 3000 px wide by 2000 px high = 3000*2000 = 6MP

Crop: 2500 px wide by 1500 px high = 2500*1500 = 3.75MP

So, the cropped image is (3.75/6) = 62.5% of the original.

Two simple multiplications, and one division, and you’ve got the answer.

Note: you can set up Photoshop to show the pixel dimensions of any open image in the status bar at the bottom of the window, so it is easy to read the before and after dimensions of the image when you crop it.

The image above is a female Redhead photographed at Veterans Oasis Park in Chandler, AZ, with a Nikon D200 and a 55-200mm lens at 200mm. The outer boundary is marked as 100% to indicate this is the full frame recorded. The Yellow line indicates 75% of the full frame (25% cropped away). The Orange line indicates 50$% of the full image (50% cropped away). The White line shows 25% of the full image (75% cropped away). It doesn’t take much cropping to toss away a significant number of pixels, and if you don’t do the actual calculation you will almost always underestimate the damage you are doing to your image.


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