Computer imaging concepts 4.

Differentiate between: 

    Bit-depth  (number of colors in each pixel)

    Resolution (number of pixels on a screen)

    Image size (height and width of image)

1.  Bit-depth  (pixels)-color intensity in each pixel.

-Bit depth is the number of bits used to describe each pixel. The greater the number of bits per pixel,  the better the image.

Bit-Short for binary digit. The smallest unit of information a computer can hold.  The value of a bit is 1 or 0.      A pixel that has one bit is black and white only.

 

A 2 bit image   2x2=4 shades .  This pixel will have 4  levels black and white and thus begins to show shades of gray.

 

A 3 bit image 2x2x2 =8 shades.  This pixel will have 8 levels of black and white (or color) and therefore can have more shades of gray.  16 colors is 4 bit.

 

An 8 bit image is 2x2x2x2x2x2x2x2= 256 shades of gray or colors (indexed or pallatized color). 

X-rays show grayscale only and therefore 8-16 bit processing is sufficient.  The human eye can perceive from 25-40 shades of gray,  while the computer can differentiate 256.

High color has 65,000 colors and is 16 bit.

True color (RGB color) has 16.7 million colors and is 24 bit. 

There is also 32 bit which is over 4 billion colors.

As you increase the color, the resolution will decrease unless you have a good graphics card with lots of memory.

Colors, bit-depth and screen resolution adjustment is located in the control panel.

2.  Resolution.

Resolution- the number of pixels on a screen (dpi-dots per inch). 

Low resolution-VGA monitors display at  640 x 480 pixels . 

SVGA monitors display with a resolution at 800 X  600 pixels and will result in a sharper but smaller image. 

XGA monitors display up to 1024 x 768 pixels.  The resolutions available depends on the combination of the quality of the graphics card, its memory and the native resolution of the monitor.

Medium resolution-Image display of around 1,280 x 1,024 (1.3 million) to 2160x1440 (3.1 million) pixels will produce good consumer prints, but not good enough for the professional photographer.

        SXGA monitors can display a resolution of up to 1,280 x 1,024 (1.3 million) pixels.

High resolution-Image display of around 4096x4096 (about 16 million) pixels are are available and are for professional use.

3.  Image size.

It is best to display images in their true resolution and size to obtain best results.   Image size is directly related to dpi and refers to the physical height and width of the image.  A 2 x 2 inch image if scaled up to 4 x 4 requires the addition of more dots to fill in missing ones and, if it is scaled down, will require removal of dots.  

Computer monitor resolution is measured by the number of pixels and scan lines.

Scan lines are used to designate resolution in a TV or video monitor.   They are a horizontal line of pixels generated by a single horizontal sweep of the beam from a monitor's electron gun. The number of scan lines that make up a frame is the vertical resolution. The TV will have around 400-525 scan lines on a screen.    A TV that is monitor quality (Sony) may have up to 700 scan lines.  HDTV  has a resolution over 1000 scan lines.

In digital television (DTV), standard-definition is good, enhanced-definition is better and high-definition is even better..

Aspect ratio: Refers to the width and height of a display. A traditional TV is 4 feet by 3 feet. A widescreen TV is 16-by-9.

Interlace vs. progressive scan: Describes how vertical lines are scanned onto a TV picture. Interlace scans all the odd lines first, then instantaneously fills in the even lines. Progressive scans all lines consecutively. The corresponding notation, ''i'' or ''p,'' follows the number of lines scanned, such as 480i or 480p.

SDTV (Standard-definition TV): A basic digital TV that displays fewer than 480p scan lines in a 16-by-9 or 4-by-3 format. This kind of set usually displays 480i, the same quality as today's analog TVs. SDTV provides 150,000 to 300,000 pixels.

EDTV (Enhanced-definition TV): A better quality picture with 480 progressively scanned lines, or 480p, which is the quality used by most DVD players. Delivers Dolby digital surround sound. Could be in a 16-by-9 or 4-by-3 format. Provides 300,000 to 400,000 pixels.

HDTV (High-definition TV): The highest resolution of DTVs with a widescreen format and scanning lines of 720p, 1080i or higher. Some of the newest sets on the market are 1080p. Delivers Dolby digital surround sound. Provides 900,000 to 2.1 million pixels.

HDTV-Ready: Describes TVs that can display high-definition TV but only when connected to a separate HDTV tuner. An HDTV-ready TV +may+ sometimes be referred to as an ''HDTV monitor.''

Integrated HDTV: An HDTV set that has the digital tuner built in so it can receive over-the-air DTV signals without a separate set-top box.

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