So, you're holding a shiny new DSLR at a party, undoubtedly one of the first things people ask is: "What's the megapixels on that thing?" In which you look down at the camera and respond "twelve I think." Before you've even raised your head you hear them murmuring as they walk away that their phone has more. Why do we have this obsession with megapixels? What is the importance of image size in relation to picture quality and when does resolution actually come into play?
What is a Megapixel?
Without getting too technical a pixel is like a puzzle piece that captures Red, Green or Blue light at various levels of brightness, creating all the perceivable colors we see today. A "mega" pixel is a million of those little puzzle pieces. So a 12 megapixel camera would be able to create an image with 12 million of these little pixels.
However the number of megapixels is only one aspect of the image quality of a camera. Other technical factors are the quality of the camera sensor and the image processor interpreting the information from the sensor. So what that means is, you could have a 20 megapixel smartphone and a 12 megapixel DSLR, and the DSLR more often than not will blow the smartphone image away.
When the Numbers Actually Matter
Often you see numbers like 1920 x 1200, or 800 x 600 on your camera display or when you have imported the images to your computer; this is the format we most commonly see when describing the resolution of a digital image. What does it mean? It refers to the amount of pixels that line the Width and Height of an image. i.e. 1920 pixels wide and 1200 pixels tall.
The resolution of an image impacts picture quality in three (3) main ways:
- The maximum size you can print, without stretching or blurring the image
- The maximum size you can view it on a screen, without stretching or blurring
- How much you can crop an image
The standard printing resolution, different from digital resolution is 300 dpi (dots per inch). Usually images are printed where one pixel equates to one dot on the page. So 300 pixels would be used to fill an inch of the print. So in a standard 4" x 6" print, it would equate to 1600 pixels x 1200 pixels or 1.92 megapixels.
Here is a chart with some common print sizes and the recommended megapixels and image resolution.
Print Size Min. Image Resolution Min. Megapixels 4"x6" 1600 x 1200 2 5"x7" 2100 x 1500 3 8"x10" 2400 x 1800 4 12"x16" 4000 x 2000 8On the screen, it's much the same way, but instead of dpi, it's ppi (pixels per inch), and the standard ppi is anywhere between 72 to 220 PPI retina screens.
The last point and possibly the most practical is the consideration of image resolution creatively- having a larger image resolution affords you the possibility to crop your image for compositional purposes. For example you wanted to take a portrait of someone but you couldn't get close enough or didn't have a long enough lens, this is where megapixels can help, it allows you to come in a little close. But how close is dependent on where you intend to display it. Is it going to be a print? If so how big? Is it just a new Facebook profile picture (500 x 500)? These considerations all come into play.
So before making a decision on purchasing a new camera or even when you are taking a photo bear in mind your intended destination and remember that the key things to a good quality image depends more on Good lighting, Correct Focus & Exposure, Lens Clarity, a steady hand and a well trained eye. So practice, practice and practice!