The Photos@VectorTrust.com Newsletter
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What is a Pixel ??
... and why do digital cameras need so many of them ??
Written by "Vector"
Managing Director, the Vector Trust
One of three founding members of the Photos@VectorTrust.com team.
Understanding Pixels is really as simple as knowing where the word ďpixelĒ comes from. Before digital cameras, before "the internet", before the word digital was common, printers would produce advertising flyers and billboards for clients. To enlarge a photo into a billboard sized advertisement, each and every "picture element" had to be proportionally enlarged and converted to a new huge size. The word "pixel" is just an industry slang term that achieved common usage. With the advent of computer monitors, a pixel became a standard to compare screen size (800x 600 ) as computers became a part of daily life. Most people now associate the word pixel with the screen resolution on a new flat-screen monitor or the digital photos taken by cameras.
Your digital photographs are made up of hundreds or thousands ( professionals need millions ) of tiny square picture elements, or pixels. The more pixels the better as youíll soon see. The "quality" of any digital picture depends in part on the number of pixels used to display the image. Pictures you print at home on "photo paper" or display on a web site depend on the density of the pixels to faithfully reproduce the subject in the picture. The technical term for this density is picture resolution. The greater the number of pixels used the greater the detail and sharpness in the picture. Resolution is measured in the scale called "dots per inch" or just dpi. Your computer monitor is probably a 72dpi screen. Some of the new flat-screen monitors are higher resolution ( Thatís why they donít fatigue your eyes as quickly.) A standard snapshot photo is printed at 300dpi in a photo lab.
Think of your home desktop printer as an "impressionist-era painter". A printer manually squirts small dots of ink in the pre-set pattern. When viewed, we donít see dots, we see a picture. Your computer screen uses tiny pixels to display this page you are reading. The computer divides your monitor into a square grid of pixels, sub-divides the image, then varies the color and brightness of each pixel in a high-tech "paint-by-number" image. Since computers only know 0ís and 1ís, not colors, this square grid of individual pixels is called a "bit map". This is another term that has leaked into common usage. Almost all photo editing programs will refer to digital photos as bit-maps. Your computer monitor "knows" that the 137th row down and the 74th pixel over is supposed to be RED. The next pixel over is supposed to be BLACK. This process repeats over and over, literally quicker that the blink of an eye. We see the picture not the pixels.
Because we canít easily see the pixels doesnít mean they arenít there. When you enlarge any digital photo, the pixels become more individually apparent. This photographic distortion is called pixelization. The more pixels there are in an image, the more it can be enlarged before pixelization occurs. To demonstrate some of these concepts, Iíve borrowed this photo of the hot air balloon launch from Ed at Tilepix.com. They do an amazing job tranforming any original photo or artwork you supply into full color, hand printed ceramic tiles. TilePix.com allows you to customise the tile floor or mural wall in your home or office with the pictures or artwork you've made. As we try to understand how pixels create a picture, think of each of the 12 individual tiles in this image as a single pixel. Together the image is complete. When viewed alone, no single ( pixel) tile would represent the image.
When you talk about your digital photographs, you can describe them one of two ways. 1) A dimensional reference is the linear count of pixels on the X and Y axis. The TilePix.com hot air balloon photo is 3x4, and the x is pronounced "by" as in "my balloon picture is three by four in size". 2) The absolute reference is a raw count of the total number of pixels. This is similar, but many times more useful because not all photos are a "standard" square shape. This example is 3 pixels, multiplied by 4 pixels for a total count of 12. Yes, I know you can easily see that in this picture, but the true pixel count of this image is dimensionally 225 x 300 or 67,500 pixels at 72 dpi. when displayed on your computer screen.
In the real world the effects of pixelization are more gradual. The image of the Energizer Bunny hot air balloon is from the Photos@VectorTrust.com staff. It was prepared specifically for display in our photo galleries at low resolution. It is 190 pixels wide by 300 pixels tall in the size displayed here. It is already "pixelated" by the fact that you are viewing it on a low resolution 72 dpi computer monitor. This image was shot on film and used in print advertising at 300 dpi. Less than 1/3 of the fine details remain, because of the limitations of your computer monitor. Iíve zoomed in to show you the blue/yellow balloon being inflated in the center of the image. In this exaggerated mode, you can see how the image of the round balloon is really only a collection of square dots, or pixels. Also notice that the Blue/Yellow balloon has individual pixels of red, orange, purple and green. Your computer monitor is working hard to display the image as "true" as possible, but is limited by the total number of pixels. Each single pixel (at this low resolution) must do "double-duty" and a blurring or "averaging" must be used.
Now that you know "what pixels are" and "why" a digital camera needs millions of them, you also understand why digital cameras are advertised as 1 megapixel, 2 megapixel or 5 megapixel models. Itís more than just advertising hype. For any picture taken, the greater number of pixels is preferable. If you intend to print pictures of summer vacation snapshots, then 2 mega-pixel cameras will give you finished prints equal to your old "point and shoot" camera. If you plan to make oversized print enlargements, manipulate the pictures in an image editor (Photoshop, CorelDraw, etc) or are an advanced hobbist photographer with high end 35mm or medium format cameras, you will be happiest with 4, 5 and 6 mega-pixel cameras. The professional press photographers you see at news events, auto races, and pro-sports games use cameras with 10mp to 16mp image captures. Just like the early days of desktop PCís, Computer power cost money. A 2MP camera with a limited zoom lens (28-100) may cost usd$175. The Minolta 7Hi model digital camera is a leader in the hottest "Pro-sumer" camera catergory. It is a 5MP capture camera with a built in zoom length lens equivilent to 35-200mm. It cost about usd$1000. Photos@VectorTrust.com staffers occasionally test equipment for manufacturers ( and write reviews). The last, latest, greatest, super-fast whiz-bang special we tested had a 12MP capture and will sell for usd$9,500 in the spring of 2004. ( All prices, retail - USA, as of Fall 2003 ). Your job as a digital camera consumer is to balence the need for photo output quality and resolution against the cost. Very few photographers need to rush out and buy a large MP digital camera, but now youíll have an understanding of the "best results" and limitations as you learn to compare digital cameras to film.
Read more about the things you should know before you purchase a digital camera in our newsletter archives. Youíll also find an article about "What you should know" before you print your own pictures at home. Every professional photographer manages the issue of image quality. With the common availability of low priced digital cameras, amatuer and hobby photographers must learn how to manage pixels too, if the family photos are going to survive in the digital world.