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| POINTS TO KEEP IN MIND WHEN PRINTING |
| Use caution when adjusting resolution settings,
as even high quality images may not print as expected if inappropriate settings are used. |
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DOTS and PIXELS
If you enlarge a digital image, when the degree of magnification exceeds a certain value, you will see that the image is not continuous, but is in fact made up of many squares called "pixels". The monitors and ink-jet printers also produce images that are composed of individual pin-points of colour, rather than continuous blends like paint. These output devices must reproduce the full colour range of the image from just a few primary colours - in the case of monitors red, green and blue - and in ink jet printers cyan, magenta, yellow, and black. The intermediate colours - the millions of shades between the primary colours - are produced by using many pin-points of primary colour ink or light to represent each image pixel. For example a certain shade of blue might be printed as seven cyan dots, one magenta and two yellows. The same blue might be displayed on a monitor as two bright blue dots, four less-bright blue dots and a medium-bright green dot. Clearly, the output device must be capable of generating more single-colour dots (ink or phosphor dots on a monitor) than there are image pixels. A confusion arises when the one term "resolution" is used both to express the number of pixels per unit of measurement (inches or centimeters) in the image and also the number of dots per inch or centimeter in the output device, as for any image, the output resolution must be greater than the image resolution. The larger this ratio, the greater the range of colours (called colour depth) that can be reproduced. |
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Printed image : each pixel composed of several dots |
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RESOLUTION
Resolution is a means of measuring the performance of devices such as scanners and printers. It is used when discussing the level of detail which can be captured by a scanner or the level of detail (smoothness) of images output on a printer, and is expressed in dpi (dots per inch) or ppi (pixels per inch). Scanner resolution is expressed in terms of the number of pixels per inch (2.54 cm) scanned from the originalimage. At higher resolutions, the number of dots per inch increases, with the result that the the image is analyzed at a higher level of detail. Printer resolution can mean both the number of image pixels that the printer will produce per line - in other words the scaling of the image onto the paper - or the number of individual pin-point ink dots per unit of linear measure. The first definition will affect the smoothness of the image, whereas the second will affect the range of colours that can be printed. |
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Low-resolution scan 
High-resolution scan |
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SCANNER RESOLUTION :
Scanner resolution is expressed as the number of pixels scanned for each 1 inch of the original. The information captured for each pixel is the intensity of the three primary colours red, green and blue. |
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PRINTER RESOLUTION :
Printer resolution is expressed as the number of pin-point ink dots printed per 1 inch (usually four colors [CMYK] of ink are used with the printer being capable of turning each primary colour ink dot off or on. A source of confusion exists in that in scanning, color and brightness information are expressed in a single pixel, whereas in printing, color and brightness are expressed using multiple dots and hence printers have larger resolutions than scanners. For example, if a printer prints four dots horizontally and vertically to represent a single pixel, the image resolution will be one quarter of the printer's resolution. For this reason, when printing an image, an actual image resolution of 1/3 to 1/4 that of the printer's mechanical resolution is sufficient. Experience tells us that a practical image resolution for many printers (typically quoted with a mechanical resolution of 1440 dpi) is 240 dpi. |
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DIGITAL CAMERA RESOLUTION :
The performance of a digital camera is the total pixel count of the CCD (the semi-conductor element which converts light to an electric signal), the part of the camera which records images. "Total pixel count" is the product of the width (X) of the CCD in pixels multiplied by the height (Y) of the CCD in pixels (X x Y). The more pixels, the clearer the image will be. The information recorded for each pixel is the brightness of each of the primary colours red, green, and blue. In addition, because the resolution of a digital camera depends on factors related to both optics and data-processing, two cameras with the same pixel count may not have the same resolution. In general, however, pixel count may be taken as a guide to resolution. In many digital cameras, the product of the width (X) of the CCD in pixels multiplied by the height (Y) of the CCD in pixels is called the "total pixel count." |
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OPTIMUM SCANNER INPUT RESOLUTION :
To print an image at the same size as the scanned original, set scanner resolution to match printer target resolution (1/3-1/4 printer's mechanical resolution). To print an image larger than the scanned original, you must set the scanner resolution higher than the target resolution, while to print an image smaller than the scanned original, you must set the scanner resolution lower than the target resolution. You can use the following system to calculate resolution. OPTIMUM INPUT RESOLUTION = TARGET RESOLUTION x (OUTPUT SIZE / ORIGINAL SIZE) | |||||||||||||||||||||||||
| * | Many scanning programs refer to target resolution as "scanner output resolution" and (OUTPUT SIZE / ORIGINAL SIZE) as "scale".
For images which will be output for viewing on a computer monitor, the optimum target resolution is 72dpi (Macintosh)-90dpi(Windows). |
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DIGITAL CAMERA OUTPUT RESOLUTION :
Since the total pixel count for digital cameras is fixed, the size at which an image will be output on a printer will be calculated from the target resolution. Take the example of a photograph recorded with a digital camera at a size of 640 x 480 pixels. To print the image at a target resolution of 200 dpi, 1 inch requires 200 dots.
Output image quality will decrease if an image is printed larger than the above calculation allows. The standards for optimum output size for images recorded with 350,000 pixel, 800,000 pixel, 1,000,000 pixel, 2,000,000 pixel and 3,000,000 pixel CCD digital cameras and printed at a target resolution of 200 dpi are shown below.
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