When it comes to megapixels, having a lot of them isn't always that important. It's easy to get confused about the number of pixels needed in an image. But, when you have to make a decision, it all comes down to how you will use the photo and the print size. Here is a helpful table to help you determine how many pixels you need to print full-sized photos on an inkjet printer or through an online printing service.
It is important to understand the terms related to image size and resolution:
- Pixels per inch (PPI): an image resolution measure that defines the size at which an image will be printed
- Points per inch (DPI): a measure of printer resolution that defines how many dots of ink are placed on the page when the image is printed
- Megapixel (MP): one million pixels, although this number is often rounded when describing the resolution of the digital camera
Less than 2 MP
Suitable for on-screen viewing and wallet-sized prints only
2 MP = 1600 x 1200 pixel
High quality: 4 x 6 inches, 5 x 7 inches
Acceptable quality: 8 x 10 inches
3 MP = 2048 x 1536 pixel
High quality: 8 x 10 inches
Acceptable quality: 10 x 13 inches
4 MP = 2272 x 1704 pixel
High quality: 9 x 12 inches
Acceptable quality: 12 x 16 inches
5 MP = 2592 x 1944 pixel
High quality: 10 x 13 inches
Acceptable quality: 13 x 19 inches
When you go above 5 megapixels, chances are you are a professional photographer using high-end equipment and you should already have an understanding of the concepts of image size and resolution.
Digital camera manufacturers make all customers believe that having a high number of pixels is always better; however, as you can see from the chart above unless you have a large format inkjet printer, a photo larger than 3MP is more than most people will ever need.
Sometimes, however, having a lot of megapixels can be useful. Many megapixels can give amateur photographers the freedom to more aggressively crop / edit their photos, when they can't get as close to the subject as they would like. The trade-off is larger files that take up a lot of camera memory space and more storage space on your computer.
The cost of the additional storage is probably worthwhile, especially in those moments when you capture an important photo and want to print it in large format to get a good shot.
Remember that you can always use an online printing service if your printer cannot handle large format prints.
The most important thing to understand is that you shouldn't increase the PPI value of a photo by increasing the image size and resolution values with Photoshop or other image processing apps.
When you do this, the final file size and image size increase dramatically and the color information in those new pixels is just a "best guess" from the computer. Bottom line, if an image has a resolution of 200 PPI or lower, it should never be printed.
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