Crop Percentages

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.

Reflections

Reflections

It doesn’t take much to make an interesting image, and it isn’t necessary to travel to exotic places if you keep an open mind and simply look around.

I’ve always enjoyed looking for patterns, and an easy way to find them is to look for simple subjects reflected in water. THis shot could have been made almost anywhere, and I bet I’ve walked past similar opportunities many hundreds of times. But on this particular day I noticed this reflection at the Veterans Oasis Park in Chandler, AZ while I was carrying a lens suitable to record it.

There’s no complicated technique involved here, nor any expensive or exotic gear. This was simply “point and shoot” with a modest Nikon D70 and a modest Nikon 55-200 “plastic” lens, hand held at 90mm and ISO 400.

Baseline your gear

Green Heron - Scottsdale, AZ

Any time I add equipment to my kit I like to find out how good it really is, so I try to “baseline” my gear to see the maximum quality I can get out of it under the best conditions. The results of this initial baseline test can then be used to measure how much image quality is lost when I move beyond ideal conditions. I’ve already talked about this here in Just Fooling Around, and also on my web site in the digital tutorial section. If you don’t know what your gear is actually capable of producing then how can you tell when you are giving up quality through sloppy technique (too high ISO, hand holding instead of using a solid support, wrong exposure, etc.) or if your gear is malfunctioning?

This Green Heron was photographed at a park near my office a week after I received my Nikon D200 – it was essentially the first chance I had to get out and take a few photos. Even though it was the lunch hour I had some luck with the light and avoided the harsh light and shadow expected at 12:32 PM when this shot was taken. The heron is down in a culvert and out of direct sun. I set the camera to the lowest ISO setting (100), locked down the movements on my sturdy Gitzo tripod, and was able to shoot at 1/60th second at f/9 using my Nikkor 300/2.8 AF-S lens and matched TC20E 2x converter (my standard birding rig). These herons are masterful at standing perfectly still, and there was no breeze to cause problems.

The resulting image has more image detail and overall quality than can be seen in this tiny 720 pixel wide image, so here’s a section of the full image viewed at 100%. This detail represents just 4% of the total pixels of the complete image.

Green Heron Detail

Whenever I start getting lazy and let the ISO creep up higher than I really need it to be I can look at this image to remind myself what I am giving up in image quality for that laziness.

If you are having issues with image quality, then it is worthwhile to step back to basics and see how good your gear might be. Set the lowest ISO available, put a quality lens on the camera and mount everything on a sturdy tripod, and photograph a stationary subject in good light. Shoot in raw and do minimal processing to the image. That’s your baseline. Then start departing from these ideal conditions one variable at a time (higher ISO, less light, questionable lens, converters, hand held, etc.) to see which step(s) rob the quality from your results.

Two views of Wilson’s Phalaropes

Wilson's Phalarope with reflection

Phalaropes are among my favorite species for many reasons. The females are more colorful than the males and act like males in many ways, leaving the breeding grounds early and allowing their mates to care for any offspring. The three species (Wilson’s, Red,  and Red-necked Phalarope) have lobed toes to help them swim like a coot of duck, and can often be found at sea far from land. They have a unique way of feeding: spinning in tight circles on the water to kick up food that they then jab at with their pointed beaks.

Wilson’s Phalarope (shown here) is the easiest to see as it occurs in good numbers in the western US in migration, and is a scarce but regular migrant in the eastern US at places like Cape May, NJ. Seen on the water they are easy to pick out from their spinning behavior; out of the water their pot-bellied shape (especially Wilson’s) makes them stand out. In basic (non breeding) plumage they look very white which also makes them stand out in a group of other shorebirds.

The top photo shows a well-marked Wilson’s Phalarope at the Gilbert Water Ranch feeding like a typical shorebird in very shallow water. I was able to get a good reflection that helped fill the space of my composition. The natural light has created a strong catchlight in the eye.

Nikon D200, 300/2.8 with TC20E 2x, ISO 200, 1/750th at f/8, tripod, 04/21/07.

Wilson's Phalarope swimming

This swimming bird was taken 3 days and about 10 miles away from the top image, and was shot from my moving blind (aka my Toyota) from the dike surrounding a shallow impoundment. Normally I would avoid water that looked like this, but I find the color of the water (from the reddish soil in the area) compliments the tones in the bird’s plumage.

D200, 300/2.8 plus 2xx, ISO 320, 1/50th at f/8, car window, 04/24/07.

Just Ducky

Redhead at Veterans Oasis Park

I don’t do a lot of duck photography here in AZ, and I did even less of it in NJ. Its not that I don’t find ducks attractive or interesting; its more that I’m still looking for a good way to compose shots that consist of just the duck and the water. Sometimes I get lucky enough to find a duck out of water, or get to work at a pond with interesting vegetation around the edges. But mostly I end up with just the duck and the water.

So, a lot of my attention goes to the look of the water, which is determined by what the sky looks like (water color comes mostly from reflection of the sky), and what might be making waves to disturb the surface.

The Redhead at the top of this post was photographed in early morning light at Veterans Oasis Park in Chandler, AZ. The sky was open and the reflected sky is rather pale. The light is over-the-shoulder “point your shadow at the bird” simple front light, so that’s mostly flattened the bird but also given a nice reflection of the duck in the foreground water. My crop/composition gives room at the bottom for the complete reflection, although it isn’t very coherent from the waves that disrupt the surface.

Ring-necked Duck female

This female Ring-necked Duck was photographed at the Water Ranch in Gilbert, AZ. Its later in the day so the sun is higher and the light is not as “warm.” The water color is a darker blue from the reflected sky. It is still mostly a front-lit situation, so there’s a strong reflection of the duck. The water has less disturbance so the reflection holds together better.