The Truth About Pixels, Part 2-1: Printing 4x3 Inch Photos
Why is a 3 megapixel camera better than a 1 megapixel camera? It really depends on how you intend to reproduce the picture. The reason cameras produce pictures at 72 pixels per inch is that this format is standard in video uses such as television and DVD. So there is no noticeable difference in quality when viewing pictures on a TV or DVD. The difference appears when you are cropping and/or printing these pictures. If you are not familiar with the term cropping, I will explain it later. First, let's talk about printing.
Even the most inexpensive of printers these days are capable of printing at 300 dots per inch (dpi). Most are capable of printing at 600 dpi and you can buy relatively affordable printers that print at 1200 dpi and above. You may have noticed that with cameras it's called pixels per inch and with printers it is call dots per inch. The terms are hardware specific, but relate to the same principal. A printer prints a specific number of dots of ink per inch on the paper whereas a TV displays a specific number of pixels per inch on the screen. In either case, combining the dots or pixels creates the picture.
So how does this affect quality? If we're printing a picture that has 72 pixels per inch from a 1-megapixel camera on 4x3 printer paper we've got a problem. (Here is where I have to crunch some numbers, so please bear with me.) Let's figure it out. Four inches times 72 pixels (dots) per inch equals 288 pixels (dots) on the vertical line. Three inches times 72 pixels (dots) equals 216 pixels (dots) on the horizontal line. The total picture would have 288 times 216 or 62,208 pixels. That's way short of one million.
So where did the other pixels go? If you're printing this picture at a store or camera shop that has conversion capabilities, the machine that you are printing on actually crunches the picture down for you. The size of the picture taken by a 1-megapixel camera is approximately 16 inches x12 inches. (16x72=1152 and 12x72=864 and 864x1152=995,328 pixels). The machine makes this picture into a 4x3 by increasing the number of pixels per inch. The 4x3 picture is 1/4th the size of the 16x12 so there has to be four times as many pixels per inch to reduce this picture to 4x3. Four times seventy two equals two hundred eighty eight pixels (dots) per inch. With more pixels or dots per inch, the picture can be reproduced at a higher quality level making details sharper and more distinct. So a 1-megapixel camera can produce a reasonably good quality 4x3 inch picture on a 300 dpi printer. That's what most amateur photographers get with their snapshot cameras. If you try to get larger pictures, then the picture quality begins to deteriorate. Part 2-2 will deal with larger prints.
Conclusion: If you have a printer with more than 300 dpi capabilities and all you want is 4x3 inch prints, then you are not using all your printer's abilities. If you want prints larger than 4x3 inch, then you need a camera with a higher quality output capability. If all you want is 4x3 inch prints and video reproduction without cropping much, then a 1-megapixel camera and 300 dpi printer should serve you fine.
Note: Different printers produce different quality prints. Since this is a discussion of pixels and digital cameras, I do not get into choosing printers for the quality. Suffice it to say, if you have a reasonably good quality printer, then the information provided should work for you.
Note 2: There are ways to enlarge prints with lower dpi rates and size and still get quality results. This information will come in later discussions and is probably geared toward the more advanced photographers and digital dark room users.
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