All About Digital Photos - What Is a Digital Photo

This article will examine the basic question, “what is a digital photo?”

DIGITAL PHOTO PIXELS
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A digital photo is made up of a series of pixels (picture elements). Most of today’s digital photos use a “24 bit RGB” system to colour each pixel. This means that each pixel has a 256 colour gradation of red, green and blue. For instance the colour orange is 255 Red, 102 Green and 0 Blue and light pink is 255 Red, 153 Green and 204 Blue. This system can produce 16 million colours which approximates what the human eye can perceive. To confuse things, many modern computers will show a screen colour of “32 bit” – this is just 24 bit RGB plus an alpha (transparency) channel. Older computers will generally show their highest setting as 24 bit (Truecolor). Either way, to properly view your 24 bit RGB digital images, you should have your computer set to either 24 or 32 bit (whatever highest display setting is offered). For more information about different modes of colour see the page about Digital Colour Models.

The dimensions of a digital photo are expressed in terms of its pixels, for instance “800 x 600” or “1520 x 1280” where the first number is the width of the photo and the second number the height of the photo. The term pixel is also used for the image sensor elements on a digital camera. Cameras are rated in terms of “megapixels” with an entry level digital camera generally offering 3 to 5 megapixels. At 3 megapixels it means that the digital resolution is about 2048 x 1536 which if you multiply the horizontal and vertical pixel dimensions comes to 3,145,728 pixels. My current camera is 8 megapixels which results in photos that are 3504 x 2336 pixels in size. Keep the digital photo pixel dimensions in mind when looking at the photos on your computer. Your computer screen is likely set to display something like 1024 x 768 pixels, meaning that when a large digital photo is displayed it is either being shrunk in size to fit your screen (in which case there may be distortion of the image) or you may have to scroll around the photo to view it in its entirety.

Individual pixels that make up a digital photo

There is a great deal of confusion in the digital world regarding the “resolution” of a digital photo. The true resolution of a digital photo is simply the photo’s dimensions in pixels. The confusion comes about from another term called “DPI” which means “dots per inch” and which some photo computer programs mistakenly call “resolution.” To be clear up front, DPI has nothing to do with digital image quality/resolution. For more full information about DPI see the various DPI articles in this section (Myth of DPI, What Print Shops Really Want, Changing the DPI

There are four main factors that determine the quality of a digital photo:
The quality of the recording device (camera's optics & sensor, scanner's sensor).

The size (in pixels) of the digital image.

The digital format it is stored in (lossless vs lossy compression).

The technical proficiency and the "eye" of the photographer.

Continue on to:
Common Digital File Formats
or
Digital Photo Acronyms and Nomenclature