Resolution
BackgroundResolution refers to the amount of information in an image. There are two ways to measure resolution. One way is to measure the dimensions of an image. That is the meaning of resolution we are probably most familiar. There are numerous scales for measuring it. If you are from the United States then you measure it in inches, if you grew up anywhere else, then it becomes, metric.
Most images (on the screen of the computer or printed on paper) are made of dots. On the computer these dots are called pixels. In the slideshow below, the first Figure represents an image of a pencil. It is actually made up of individual pixels use the slideshow to see a representation of this. What you will see is a magnified section of the original image and instead of displaying dots, it will display large squares as representations of the pixels. The actual dimensions of that Figure are 500 by 352 pixels. That is one kind of resolution. There is another aspect of resolution which is the number of dots per inch (dpi). On the screen this should be referred to as ppi or pixels per inch. (Technically ppi is different from dpi but for our discussion these terms will be used interchangeably.) The term, dpi is a unit of measurement which represents the number of dots per inch. In the case of a computer screen the resolution is typically 72 or 96 dpi, depending on your setup. Most images that you see on the screen of the computer are at this resolution. However, it is possible to have a higher dpi image than what can be seen on the screen. For instance, have a look at the following three Figures below.
The Figures above are identical images except for the difference in dpi. The first Figure is set to 30 dpi and takes up 23 K of memory, the second Figure 3 is set at 72 dpi and takes up 31 K of memory, and the last Figure is 150 dpi and takes up 115 K of memory. The 30 dpi Figure looks blotchy because there is not enough resolution to display the details on the screen. The second and third Figures look the same on the screen but the last one is 150 dpi (only display 72 dpi). This last Figure would produce a better hardcopy printout because it has a higher resolution. For printing the preferred resolution is often 300 dpi, that level of resolution will produce photo quality results but is overkill for a computer screen.
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PurposeResolution is critical to serve the purpose of the medium and have the image look good but not be so large it slows the system down.
ImplicationsThe implications of resolutions is to know how the image will be used. What medium will be used to output the results?
However, if the image would have been large to begin with, it is fine to shrink it, see the following slideshow as an example:
The rule of thumb is always start large and then resize to something smaller. Never start small and enlarge (there are exceptions). Note, it is possible to resize large images (dimension wise) with a lower dpi setting to smaller images with higher dpi settings or do the reverse of that.
always start large and then resize to something smaller Megapixels as resolutionDigital cameras are often rated in megapixels. This term refers to resolution. The higher the megapixel the larger the dimension of the images. For instance if you want a 4X6 inch photo at 300 dpi what size of camera would you need? Here is the math:
= width x height = 4x300 x 6x300 1200 x 1800 = 2,160,000 pixels or 2.16 megapixels A 5 megapixel camera would allow for a much larger printout at 300 dpi. Most modern cameras provide enough megapixels to accomplish most purposes, so quality is determined by other criteria like the size of the sensor and the quality of the lens. The quality of the lens is more important than megapixels. |