Resolution Explained
Contents |
| Digital Camera Monitor Inkjet printer Scanner |
Digital Camera Resolution |
| A typical 7 mega pixel camera gives an
image size of 3072 x 2304 pixels. This represents the amount of
detail that can be captured by the camera CCD (charge coupled device).
This detail can be stored on the camera as a raw file (e.g. TIFF).
Alternatively, to reduce the amount of memory, it can be compressed
(usually in jpeg format) by the camera to give file sizes that are more
easily handled by the camera memory card and computer. The compression options on the camera are typically called High, Fine, Normal and Basic. |
Monitor Resolution |
| Monitor resolution refers to
the number of pixels comprising the image on the screen. The
monitor screen resolution on a PC can be set up through Microsoft
Windows - My Computer - Control Panel - Display - Settings. For
example a screen resolution of 1152 pixels wide by 864 pixels
high might be selected which would mean an image imported with
this dimension would fill the entire screen. An image of size
around 600 x 450 pixels would only fill a quarter of the screen.
A practical screen resolution for say a 17 inch CRT monitor is around 1024 x 768. A 17 inch CRT monitor has a viewing area of approximately 12.5 inches wide by 9.5 inches high. Dividing the number of pixels by the number of inches gives a resolution of 82 pixels per inch. Therefore, in this example, for monitor viewing there is nothing to be gained by having an image resolution greater than 82 ppi. Usually 72 ppi is a default used in most imaging software. LCD monitors are now becoming cheaper and more popular. They have a native resolution that they should be used at. A resolution of 1280 x 1024 pixels is common on 17 inch LCD monitors. It is also used on larger 18 and 19 inch monitors. Therefore the larger monitor has less relative definition. 15 inch LCD monitors have a native resolution of 1024 x 768 pixels which gives the same dpi (dots per inch) as the 17 inch. |
Inkjet Printer Resolution |
| Working backwards. Good quality inkjet printers
have print resolutions in excess of 1440 dpi (dots per inch). A
printed output image is made up of numerous coloured pixels. Each
coloured pixel is formed by the printer depositing between 4 to 6
dots (depending on the number of inks) onto the paper. Therefore
1440 dpi produces 1440 divided by 4 to 6 to give ppi (pixels per inch). That is roughly 380 to 240 ppi resolution.
This resolution is
beyond the capability of the naked eye and in fact many say that
the quality of a printed image at around 200 ppi is more than
acceptable. The printer resolution is therefore not the limiting
factor for viewing by the naked eye. A printer operating at 1440
dpi can only give a maximum resolution of around 300 ppi whilst a
printer operating at 720 dpi can only give a maximum resolution
of around 150 ppi. In other words there is little point in producing a printed image with a resolution greater than say 300 ppi. Most modern printers are easily capable of this. The quality of output then depends on the inkjet system used by the manufacturer and the colour management system. |
Scanner Resolution |
| Let us consider flat bed scanning. Take an example of a scanned 6 x 4 inch source image and a required printed output of the same 6 x 4 inch size at maximum printer quality. Scanning at 300 dpi will give an output print with the required 300 dpi resolution, from a 1440 dpi printer. If the printer resolution is selected to be 720 dpi then the best output image resolution will be reduced by a half to around 150 to 190 ppi. Likewise if the 6 x 4 inch source image is to be enlarged to say 12 x 8 (a 200 % linear enlargement) then the printed output from a 1440 dpi printer will be 300 divided by 2. That is 150 ppi. To compensate for a linear enlargement of 200 %, the source image would need to be scanned at 2 x 300 dpi linear resolution. i.e. 600 dpi. Conversely if a 12 x 8 inch source image is to be reduced in size to a 6 x 4 printed output, then the scanning resolution need only be 300 divided by 2. i.e. 150 dpi. The scanner application software often makes this easy for the user by enabling the image source size and required output size and resolution to be predefined. The scanner then scans at the required resolution. |
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Digital Camera Monitor Inkjet printer Scanner