August 30, 2009

How Many Megapixels Are Enough?

Now that you know what a megapixel is, the next question is how many do you need? The answer depends on what you're going to do with your picture.

If you're going to share your photo by email, Facebook, Flickr, or other web page, then you need very few megapixels at all.
How many of you have received a message that took two days to download? And after it arrived, all you could see was an eye?!

When you display a digital photo on a computer screen, each image pixel becomes a screen pixel. Almost no one has a monitor with a million pixels on it. So if you send even a 1 megapixel photo, your recipient won't be able to see the whole thing without scrolling (the eye mentioned above).

Original 6 megapixel picture with too many pixels for screen display

In addition, the more pixels in your photo, the bigger the size of the file. If you have too large a file, then it takes a long time to upload from your computer and a long time to download on your recipient's computer, whether as an email message or a web page (the two-day download).

So email photos need very few pixels. I recommend a maximum size of 800 pixels on the longest side to ensure you have a small image that will be completely visible on the screen and transfer quickly from your computer to theirs.


Photo reduced to 800 pixels on the long side for screen display

If you are going to print your picture, either with your own inkjet printer or from a photo lab, then you need lots more pixels! When you print a digital photo, the pixels must be small enough and close together enough so they become invisible. Otherwise, you would see squares like a mosaic instead of a photo.

I recommend you have at least 200 pixels per inch of printed photo. So if you want a 4x6 inch print, you would need a digital photo that has at least 800 pixels x 1200 pixels (4 inches x 200 pixels per inch = 800 pixels; 6 inches x 200 pixels per inch = 1200 pixels). In fact, you almost cannot have too many pixels for printing. The more pixels in your digital photo, literally the larger you can print it and keep all the details sharp.

If you've been reading carefully, you may have noticed that the recommendations for an email photo are very different from those for a printed photo. To refresh your memory:

  • Email/Web Photo --- Maximum Size 800 pixels on longest side
  • Printed Photo --- Minimum Size 200 pixels per printed inch
    (800 pixels x 1200 pixels for a 4x6 inch print)
So what do you do? I recommend that you always use all the megapixels that your digital camera can make when you are shooting. After the pictures are on your computer, then you can make a COPY of your photo and change the number of pixels to suit your purpose.

This method works best for digital images because they retain their sharpness and color better when you shrink the size of the photo instead of enlarge it. In addition, if you have more megapixels than you need, even for a printed photo, then you can crop the picture (cut away some pixels on the outer edges) and still have enough pixels left over to make a print.