Introduction
The primary properties of visible light are intensity, propagation-direction, frequency or wavelength spectrum and polarization, while its speed in a vacuum, 299 792 458 m/s, is one of the fundamental constants of nature.
Materials can be classified based on how it responds to light incident on them:
1. Opaque materials – absorb light; do not let light to pass through
2. Transparent materials – allow light to easily pass through them
3. Translucent materials – allow light to pass through but distorts the light
during the passage.
1. Reflection
• Light follows the Law of Reflection: “The angle of incidence is equal to the angle
of reflection.” Light can bounce off materials in two ways:
a) Diffuse reflection – reflected rays go in different directions; happens in rough
textured or uneven surfaces
b) Regular/Specular reflection – reflected rays go in one directions; happens in
smooth and shiny surfaces; image can be seen
2.Refraction
• Light bends/refracts when it changes speed.
• This usually happens when the light travels from one medium to the next.• Simple rule of thumb in refraction:• If light slows down, it will refract towards the normal line.• If light speeds up, it will refract away from the normal line.• Light travels faster in air, slow in water and slower still in glass.• The slower light is in a medium, the more it refracts/bends in it.• The measure of how much light refracts in a medium is called index of refraction.• the refractive index n is defined as the ratio of the sine of the angle of incidence to thesine of the angle of refraction; i.e., n = sin i / sin r.• Refractive index is also equal to the velocity of light c of a given wavelength in emptyspace divided by its velocity v in a substance, or n = c/v.
3.Dispersion of Light
Dispersion of light can be defined as the splitting of white light when it passes
through a glass prism into its constituent spectrum of colors (i.e. violet, indigo, blue, green, yellow, orange and red). Dispersion figuratively means ‘distribution’.
4.Total Internal Reflection
Total internal reflection (TIR) is the optical phenomenon when waves travelling in one medium strike at sufficiently oblique incident angle (called the critical angle) against the boundary with another medium of lower refractive index, instead of transmitting into the second ("external") medium at a refracted angle
•TIR occurs when light is reflected completely at the boundary between two mediums.
5. Diffraction
Diffraction refers to various phenomena that occur when a wave encounters an obstacle or opening. It is defined as the bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a secondary source of the propagating wave. Italian scientist Francesco Maria Grimaldi coined the word diffraction and was the first to record accurate observations of the phenomenon in 1660.
• Diffraction is the slight bending of light as it passes around the edge of an object.
The amount of bending depends on the relative size of the wavelength of light to
the size of the opening.
• If the opening is much larger than the light's wavelength, the bending will be
almost unnoticeable. However, if the two are closer in size or equal, the amount
bending is considerable, and easily seen with the naked eye.
Types of Graphics Format
1. Raster Graphics
• A raster image comprises a two-dimensional grid of pixels, each pixel having a specific color value. A simple example is shown below:
• Example of raster graphics file formats are JPEG, PNG, APNG, GIF, and MPEG4.Vector graphics are commonly found today in the SVG, EPS, PDF or AI graphic file formats
Vector Graphics
• Vector graphics formats store images as mathematical representations of image elements, such as shapes or lines.• For example, a line segment might be defined in terms of the coordinates of its starting point, a
direction, and a length. More complex shapes can be built up from simple shapes.
• Enclosed shapes can also be filled with colors.
• Some vector formats support 3-D objects as well, such as wire frame models.
• Vector formats are most commonly used in the field of Computer-Aided Design (CAD), since
they are ideally suited to the creation of architectural and engineering drawings, maps,
schematics, and charts.
• They also form the basis for 3-D modelling and animation, although this is beyond the scope of
this Guidance Note.
• Vector files can be easily manipulated, and rescaled without loss of quality.
• The size of a vector file is proportional to the complexity of the image (unlike raster images).
• Vector files do not usually support compression. However, vector file sizes are typically far
smaller than the equivalent raster image.
More specifically, a vector graphic is an artwork made up of points, lines, and curves that are based upon mathematical equations, rather than solid colored square pixels. This means no matter the size or how far zoomed in the image is, the lines, curves, and points remain smooth.
Graphics Interchange Format (GIF)
• The current version, GIF89a, was released in 1990.
• It supports color depths from 1-bit (monochrome) to 8-bit (256 colors)
• always stores images in compressed form, using lossless compression.
• Other supported features include interlacing and transparency.
JPEG File Formats (JFIF and SPIFF)
JPEG itself is not a file format, but rather an image compression algorithm developed by the Joint Photographic Experts Group in 1990.
• The original specification did not describe a file format for data exchange. However, theIndependent JPEG Group and C-Cube Microsystems developed a JPEG File Interchange
Format (JFIF) in 1992, which has become a de facto standard; this is what is commonly
referred to as the JPEG file format.
• In 1996, Part 3 of the JPEG standard was released, containing the specification for an
official file format, called SPIFF (Still Picture Interchange File Format). This is more
complex than JFIF, and it also supports other compression schemes.
• The JPEG algorithm is also supported by a number of other raster image formats,
including TIFF.
• JFIF and SPIFF are 24-bit color formats and use lossy compression, although a lossless
extension to JPEG is also available (but not widely used).
• JPEG is particularly suited to the storage of complex colors images, such as
photographs.
3. Portable Network Graphics (PNG)
• It supports color depths from 1-bit to 48-bit.
• Image data is always stored compressed, using a variation on the lossless LZ77- based deflate compression algorithm which is not patented, and therefore free to use.
• Support for interlacing and transparency is also provided, and the format incorporates a number of error detection mechanisms.
• The PNG specification is entirely public domain and free to use.
4. Tagged Image File Format (TIFF)
• Aldus first published the specification in 1986. When Adobe Systems Incorporated purchased Aldus in 1994, they acquired the rights to the TIFF specification, and have maintained it since then.
• The current version of the specification (revision 6.0) was released in 1992.
• TIFF supports color depths from 1- bit to 24- bit (e.g. monochrome to true color), and a wide range of compression types (RLE, LZW, CCITT Group 3 and Group 4, and JPEG), as well as uncompressed data.
5. AutoCAD Drawing Format (DWG)
• As a result, AutoCAD’s native drawing format, DWG, has become a de facto standard for vector graphics.
• The DWG specification is revised with each release of AutoCAD: the original version being released with AutoCAD 1.0 in 1982, and the latest version being AutoCAD 2007.
• DWG supports 24-bit color depths (True Color) and 3-D models.
• The DWG format is proprietary to Autodesk and has not been released.
• Instead, Autodesk recommend the use of the DXF format for data exchange.
• Nonetheless, DWG has become a de facto standard for the exchange of CAD data, and is
supported by most CAD packages, albeit with varying degrees of fidelity.
• according to current estimates there are in excess of 4 billion DWG files in existence
worldwide.
6. AutoCAD Drawing Exchange Format (DXF)
• The DXF specification is revised with each release of AutoCAD: the original version being released with AutoCAD 1.0 in 1982, and the latest version being AutoCAD 2007.
• DXF files can be encoded either in 7-bit ASCII or binary.
• They support 8-bit color depths (256 colors) and 3-D shapes, and are uncompressed.
DXF is a complex format, and the quality and sophistication of its implementation in
different applications varies considerably.
• The frequent changes to the specification can also cause compatibility problems.
• In particular, users must be aware that some applications may read a DXF file whilst skipping unsupported features. This can lead to the loss of information in a manner that may not be obvious to the user.
• The DXF specification is owned by Autodesk, but is freely available to use. It is widely used for the exchange of vector data between different applications and platforms.
Activities
For more details of properties of light and Types of Graphics Format please visit the following sites-
https://youtu.be/ruFyaM9BsLM
https://youtu.be/bP4i1KUfB3o
https://youtu.be/Yky_knLKzqU
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