Megapixels and Size

WHAT IS A MEGAPIXEL?

A pixel, px, is a single square of color that composes a digital image. A megapixel, MP, is one million pixels. When dealing with images, your end usage will determine the megapixel requirement of the camera that’s capturing it.

As of this writing, the average $100 point-and-shoot camera is 10MP. Professional SLR cameras costing $500-$5000 on average gets you 10-20 MP. I won’t go into the cost of our 33 MP Leaf Aptus 75 camera back.  These are just estimates and costs of cameras vary on features that would have to be covered in a different article.

Printing uses the term dpi, or dots-per-inch, which is the physical equivalent of pixels-per-inch for simplicity’s sake. The average hi-res print is run at 300dpi, while your computer’s monitor displays at 96 ppi on average.

MY IMAGE IS GOING TO PRINT

I found that most sites give you a print size at the end of a chart based on a megapixels or resolution. I feel it’s more appropriate to show the numbers based on your end usage/size first.

Key:

Print Size (at 300dpi); Resolution; Minimum Megapixel Camera

4″x6″ print; 1200px X 1800px; 2.2MP

5″x7″ print; 1500px X 2100px; 3.2MP

8″x10″ print; 2400px X 3000px; 7.2MP

11″x14″ print; 3300px X 4200px; 13.9MP

16″x20″ print; 4800px X 6000px; 28.8MP

These are the numbers for optimal image quality. You can always trade size for resolution, essentially making it “blurrier” the larger you scale it up. Also, image quality is affected by the camera’s settings, sensors, etc.

MY IMAGE IS GOING ON THE WEB

This is the medium where you don’t need a lot of horsepower capturing an image. Your saving grace is that most websites are no larger than 1000 px wide.  That means any point-and-shoot camera would have the resolution for use on web. You’ll notice some people use a cell phone camera that’s 1-3 MP when quality is not of the essence.

FINAL THOUGHTS

There are many ways you can make an image look bad. In order to get the best quality image for your end usage, please do not commit these as well as other offenses I’ve seen in the past:

• Scaling up more than 200% and expecting perfect clarity.

• Assuming dark areas in a shot will look good when you make it lighter in Photoshop and vice-versa.

• Supplying a hi-res image only to use a 1″ x 1″ crop of it to be scaled up for printing a large size.

• Supplying a jpeg to a retoucher when you have a .RAW, .CR2 or .NEF on hand.

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