022 July 2, 2010 Your Pixels Are Showing
Your Pixels Are Showing! That’s a bad thing. Right? Well, Yes and No. Since all digital pictures are made of pixels, it’s a good thing. If you can actually see the pixels in the image, it’s probably a bad thing. This could take a little explanation, so bear with me.
The pixel is the smallest addressable element of a digital image. For illustration, let’s go to some old technology and compare a pixel to the dots that make up a black and white image in a newspaper. If you look closely at that B&W newspaper image, you’ll notice rows of dots; the resolution of the image (that is, how fine detail appears in the picture) is determined by how large the dots are and how many can be placed within an inch (DPI). To state the obvious, the larger the dots, the fewer that can be placed per inch and the lower the resolution. Typically, a newspaper will use a resolution of 60 to 80 dots per inch. Now take a look at a black and white image in a glossy page magazine. At first glance, you notice that it shows finer detail; at closer examination, you’ll see smaller dots and more dots per inch (higher resolution). The resolution on the glossy page is usually about 150 DPI. A color picture in a newspaper or magazine will show the same matrix of dots, but will use four colors; by overlapping the four colors – cyan, magenta, yellow, and black (CMYK) the printed picture can effectively represent most colors. Again, the glossy magazine uses smaller dots (higher resolution), and shows better detail than the newspaper photo. You’ve probably caught the connection already: in print media, the dot is the smallest addressable element of a printed image.
Now let’s examine another old technology – take a close look at a very good photograph or color slide. The photo probably doesn’t show any “dots” until it’s magnified enough to see the actual grains that created the image.
Now, back to pixels. Ideally, you want your digital picture to display as smoothly as a very good photograph; for this quality, you’ll need small pixels and high resolution – a lot of pixels per inch (PPI). There will be a difference if the image is intended to be displayed on a monitor or printed. For a high quality printed image, I usually plan on providing 300 PPI for each inch of printed image. For example, if the photographic print will be 8”x 10”, I want to provide a file that is 2400 pixels x 3000 pixels (8x300=2400, 10x300=3000). I may use a compression of up to 10% to make the file smaller; although, too much compression will cause the print quality to decline.
If the image is to display on a monitor, I plan on 72 PPI per inch of monitor display. If the display is to be 10” x 8”, plan on a file that is 720 pixels x 576 pixels. This file can be compressed up to 10% without an obvious loss in quality. If the image is to be emailed, you could compress it a little more (up to 30%) in the interest of uploading more quickly. Generally, a 720x576 pixel image will fill a monitor display – depending on the resolution settings that the monitor uses.
How does all this affect taking a digital photo with your camera? What if you have a great pict that you email to Aunt Agnes AND you want to make a high quality 8x10 print from that same photo? The file that your camera saves must be large enough to accomplish the more demanding application – that is, making the print. If your camera is set for smallest file size, chances are the file will look pretty good as an emailed photo. BUT – if you try to print from that file, the print process will either have to enlarge the pixels to fill the print or take a guess to fill in enough pixels for the print. (In my examples above, the difference between 576 pixels wide and 2400 pixels wide is quite large! For each pixel in the 576 pixel display, the print process would have to create almost four more pixels for each existing pixel to equal 2400 pixels wide.) In this case, the quality from the pixels of the smaller image would be showing and the print quality declines – this is a bad thing.
Tip #1: Set your camera for largest file size for best print quality.
Tip #2: Use computer software to resize files for the application needed.
Tip #3: Computer software can make an image smaller without losing quality, but cannot retain quality when making the image larger.
Tip #4: Largest file size setting means less picts can fit on the camera’s memory card. Purchase a spare card for when the first one gets full.
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