Resolution And Refresh rate

Resolution:

Refers to the sharpness and clarity of an image. The term is most often used to describe monitors, printers, and bit-mapped graphic images. In the case of dot-matrix and laser printers, the resolution indicates the number of dots per inch.

• For example, a 300-dpi (dots per inch) printer is one that is capable of printing 300 distinct dots in a line 1 inch long. This means it can print 90,000 dots per square inch.For graphics monitors, the screen resolution signifies the number of dots (pixels) on the entire screen.
• For example, a 640-by-480 pixel screen is capable of displaying 640 distinct dots on each of 480 lines, or about 300,000 pixels. This translates into different dpi measurements depending on the size of the screen.
• For example, a 15-inch VGA monitor (640x480) displays about 50 dots per inch.Printers, monitors, scanners, and other I/O devices are often classified as high resolution, medium resolution, or low resolution. The actual resolution ranges for each of these grades is constantly shifting as the technology improves.

Resolution of digital images:
The resolution of digital images can be described in many different ways.

Pixel resolution:

The term resolution is often used as a pixel count in digital imaging, even though American, Japanese, and international standards specify that it should not be so used, at least in the digital camera field. An image of N pixels high by M pixels wide can have any resolution less than N lines per picture height, or N TV lines. But when the pixel counts are referred to as resolution, the convention is to describe the pixel resolution with the set of two positive integer numbers, where the first number is the number of pixel columns (width) and the second is the number of pixel rows (height), for example as 640 by 480.

Another popular convention is to cite resolution as the total number of pixels in the image, typically given as number of megapixels, which can be calculated by multiplying pixel columns by pixel rows and dividing by one million. Other conventions include describing pixels per length unit or pixels per area unit, such as pixels per inch or per square inch. None of these pixel resolutions are true resolutions, but they are widely referred to as such; they serve as upper bounds on image resolution.

Below is an illustration of how the same image might appear at different pixel resolutions, if the pixels were poorly rendered as sharp squares (normally, a smooth image reconstruction from pixels would be preferred, but for illustration of pixels, the sharp squares make the point better).

An image that is 2048 pixels in width and 1536 pixels in height has a total of 2048×1536 = 3,145,728 pixels or 3.1 megapixels. One could refer to it as 2048 by 1536 or a 3.1-megapixel image.

Refresh rate:

The Refresh rate is the number of times a display's image is repainted or refreshed per second. As it denotes a frequency of a process, the refresh rate is expressed in hertz. That is, a refresh rate of 75 Hz means the image is refreshed 75 times in one second. For academic interest, it should be kept in mind that refresh rate is different from frame rate in that refresh rate means the repeated illumination of identical frames, while frame rate measures how often a display image can change into another.The refresh rate is also referred to as the scan rate, vertical scan rate or the vertical refresh rate.

Calculating Maximum Refresh Rate:
Where VSF = vertical scanning frequency (refresh rate) and HSF = horizontal scanning frequency the formula for calculating a CRT monitor's maximum refresh rate is:
VSF = HSF / number of horizontal lines x 0.95
So, a monitor with a horizontal scanning frequency of 96kHz at a resolution of 1280x1024 would have a maximum refresh rate of:
VSF = 96,000 / 1024 x 0.95 = 89Hz.
If the same monitor were set to a resolution of 1600x1200, its maximum refresh rate would be:
VSF = 96,000 / 1200 x 0.95 = 76Hz.

Дата добавления: 2015-10-28