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Image Resolution 101

Resolution is one of the toughest concepts to understand, it’s also the most important concept to grasp when it comes to printing photos that look good.

When you open a photo in an image editor such as Photoshop Elements and use the zoom tool colored squares will become more and more distinctive as you continue to blow up the photo. These blocks of solid colors are called pixels (picture elements) and are what forms the image you see on your screen. The setting on your camera will determine the size of these pixels, better quality will have more but smaller pixels.

The photos below demonstrate the difference between pixel sizes, the 72 ppi blow up looks like Lego blocks and is not really distinguishable, the 200 ppi blow up still gives us an idea what the object is though blurry.

Low quality image at 72 Pixels per Inch

Higher quality image at 200 Pixels per Inch

The measurement that controls pixel size is called resolution. Ideally we want the pixels to be so small that when a photo is sent to a printer they’re small enough so that they can’t be seen by the naked eye.

In printing, resolution is measured in dots per inch (dpi) because most printers print dots. For onscreen images on your computer monitor resolution is measured in pixels per inch (ppi).

Resolution doesn’t really mean much unless your photo is sent to a printer. When you print a low-resolution image (72 ppi) it will look blocky, whereas a higher resolution photo will look sharp.

Computer monitors will display both images equally well because the video driver, the software that controls what you’re seeing on the screen is controlling the resolution for the display. That’s why resolution is so confusing, you just can’t see resolution changes onscreen.

For printing the rule of thumb is that photos should always be at 300 dpi. Bare in mind that converting a 72 dpi picture to a 300 dpi picture doesn't make the resolution better unless the dimensions are reduced. A 24" X 36" photo reduced to 4" X 6" will look fantastic, but if you convert a 4" x 6" 72 dpi image to a 4" x 6" 300 dpi image, it will still look pixelated and blurred.

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