Tag Archives: pixels per inch

Understanding Photos and Resolution: a Brief Primer

11 Apr

As a graphic and web designer, I frequently work with photos, both digitally (for the web) and in print. Many of the photographs I use come from everyday users snapping a quick pic with their cell phone or a point and shoot camera. But if users don’t have some understanding of resolution and pixels, images captured this way may be unusable in a particular medium.

So what is resolution and why do printed images need a higher resolution than those displayed on the web?

Pixel dimensions measure the number of pixels across a photo’s height and width. Resolution is measured in pixels per inch (ppi). Resolution is basically how much detail the image holds. The higher the resolution, the sharper the image.

A printer is a high-resolution device. Generally, for printing an image a resolution of 300 pixels per inch will yield a clear image. Sometimes even 240 pixels per inch will produce an acceptable print.

A monitor, unlike a printer, is a low-resolution device. 72 ppi is the standard for digital images. That is why you cannot successfully create a sharp print with an image pulled from the web (unless you make it very small).

Another consideration with images is the file size. For web, a smaller file size will load faster. If we have roughly three seconds to capture a user’s attention, pages need to load quickly. Since file size is directly related to the pixel dimensions of an image, the higher the resolution, the larger the file size. So one could use high-resolution images on the web, but they would be very slow to load.

Another consideration when processing images is that different file formats also contribute to the size of an image. (Different formats use different file compression methods; compression can also mean loss of data.)

A good rule of thumb is this: shoot the image in the highest resolution your camera will allow. One can always crop an image, but you can’t create detail (additional pixels). This way, the image can be used in print or digitally.



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