Monklands Memories - Airdrie & Coatbridge areas

 

All about Pixels

Pixel? is short for ?picture element?.  A pixel is the smallest piece of information a digital image is made from. Your computer display uses separate red, green and blue (RGB) ?dots? arranged very close to one another and together display the full color spectrum.  Depending on the resolution your display is set to, several clusters of RGB dots make up a picture element or pixel. A fifteen inch monitor set to a screen resolution of 800 pixels horizontal x 600 pixels vertical has 480,000 pixels in total; a 17 Inch monitor set to 1024 pixels x 768 pixels has 786,432 pixels total.  Your display resolution can be set through the Control Panel in Windows.

A digital camera uses a device called a Charge Coupled Device, or CCD, to capture the image.  CCDs are made up of millions of tiny light sensors arranged in a matrix that capture the full RGB color spectrum. A camera with 3.3 megapixels (millions of pixels) has a matrix of (approximately) 2048 pixels horizontally and  1536 pixels vertically.  The table below shows the pixel resolution commonly available on digital cameras.

These numbers may vary somewhat from model to model.  For example, one camera may have 5.0 megapixels and another 5.1 megapixels. One may have 3 megapixels and a competitor claim 3.3 megapixels.

As is evident, a digital camera has many more pixels than a PC display in both horizontal and vertical axis.  If we took a 2048 x 1536 pixel image directly from a 3 megapixel camera, and attempted to view it directly on a display with resolution 800 pixels across and 600 pixels down, we would only be able to view a small portion of the photo at a time.  Most image viewing software is smart enough to adjust things so that you can have the entire photo ?fit to screen?, but if you view the actual pixels, the display would only show a portion of the actual image.

The PC display is not a very high-resolution device compared to your camera.  In fact, the average display only has a resolution of about 72 to 80 pixels per inch  (ppi) horizontally.  So when you are preparing an image for displaying in an email or on a web site, there is little advantage to have it at a higher resolution than about 80 pixels per inch.

When sending an image via email, it is good practice to resize the image to 640 x 480 pixels (or close to this).  Since the resolution of a typical PC display is 72 to 80 ppi, a 640 x 480 image displays as approximately 8 inches by 6 inches ? a good size for viewing.  After re-sizing to 640 x 480, the file should be saved at a lower JPEG compression level to yield a small file size suitable for email ? particularly on dial up connections.  Note that re-sizing does not imply cropping the image; we are simply scaling down a high pixel count image to a lower pixel count to represent the same content but at lower resolution. You will be surprised how good a low resolution, (72ppi) highly compressed image looks on your screen.

How Many Pixels Do I Need? That said, there's still a bigger question: What resolution do you need? What do you intend to do with the photo after you take it? If it's headed for e-mail, the Web, or a slide-show application, then you only need a megapixel or less. If you want to send the photo to your ink jet photo-quality printer, then you'll need about 200 or 250 pixels for every inch you want to print. An 8-by-10-inch print, then, should measure about 2000 by 2500 pixels. You can send a smaller image to the printer, but if you skimp on pixels you'll probably see jaggies in the final print. I suggest that you set your camera to its highest resolution and leave it there. Why? Because that way you can crop your photos and still have enough resolution for sharp-looking prints. Think of your image editor as a sort of after-the-fact zoom lens. With megapixels to spare, you can inspect your photo on the PC and cut away the extraneous, the distracting, and the unneeded. You're left with a tight, impressive photo that you can print or process however you like. If you throttle down the camera's resolution to begin with, the image will have only enough pixels to print sharply if you don't do anything to the image. Cut away half the picture to eliminate a distracting object on one side of the scene, though, and now you'll have to "stretch" the image to print it at the same size. The result is that your image will look jagged, blocky, and blurry.   Remember: In digital photography, more pixels are always better than less.

 

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