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MULTIMEDIA TECHNOLOGYGRAPHICS AND
IMAGES
Dr. Zeeshan Bhatti
BSIT-IIIChapter 2
BY: DR. ZEESHAN BHATTI 1
GRAPHICAL IMAGES
Graphical images obviously play a very important role in multimedia pieces
• Images may be photograph-like bitmaps, vector-based drawings, or 3D renderings
• Tools for image management focus on different kinds of images and converting between formats peculiar to different tools and platforms
BY: DR. ZEESHAN BHATTI 2
BITMAP AND VECTOR IMAGES Internal model of the image Could be an array of pixels or A mathematical description of lines, curves and shapes
Still images are generated in two ways: bitmaps (or raster-based) or vector-drawn
BY: DR. ZEESHAN BHATTI 3
Bitmap Images A bitmap is a matrix describing the individual dots that are the smallest elements (pixels) of resolution on a computer screen or printer or we can say a bitmap image is an array of logical pixels.
• monochrome just requires one bit per pixel, representing black or white
• 8 bits per pixel allows 256 distinct colors, 16 bits per pixel represents 32K distinct colors, 24 bits per pixel allows millions of colors
BY: DR. ZEESHAN BHATTI 4
BITMAP IMAGES
BY: DR. ZEESHAN BHATTI 5
• What’s the tradeoff? more bits provide more color depth, hence more photo-realism, but require more memory and processing powerSettling for just 256 colors forces someone to decide, which colors?
• Graphics production software may capture in 24-bit color and convert to 8-bit
• GIF and PNG formats use a 8-bit color table allowing up to 256 colors
• JPG preserves more color depth with 16 bits per pixel
• Photoshop file (PSD) preserve 24 bits or more per pixel
BY: DR. ZEESHAN BHATTI 6
VECTOR IMAGES A vector-drawn image is created from geometric objects such as lines, rectangles, ovals, polygons using mathematical formulas Mathematical description of lines, curves and shapes Requires computation to determine logical pixels Compact, scalable, resolution independent and easy to edit Based on co-ordinates and algorithms Description is infinitely thin Computation chooses logical pixels Anti-aliasing to fix jaggies Basic blocks Squares, polygons, ellipses, lines, bézier curves… Easy to manipulate Scale, skew, rotate…
BY: DR. ZEESHAN BHATTI 7
VECTOR IMAGES
BY: DR. ZEESHAN BHATTI 8
e.g., RECT 0,0,300,200,RED,BLUE says (using Cartesian coordinates)
“Draw a rectangle starting at 0,0 (upper left corner of screen)
going 300 pixels horizontally right and 200 pixels downward,
with a RED boundary and filled with BLUE
Figure: A Vector image Showing Bezier Curve BY: DR. ZEESHAN BHATTI 9
WHY MIGHT A VECTOR-DRAWN REPRESENTATION USE LESS MEMORY THAN A BITMAP? The first popular vector-drawn images were for computer-aided design (CAD)
such as AutoCAD, for aiding engineers and artists in creating complex renderings
Graphic artists designing for print media use vector-drawn objects because they put rectangles and Bezier curves on paper without jaggies, exploiting high resolution printers
Macromedia Freehand, Corel Draw & Adobe Illustrator are vector-drawing applications Macromedia Flash puts vector-drawing on the Web with a plug-in
BY: DR. ZEESHAN BHATTI 10
RASTERIZING
Converting between bitmaps and vector-drawn images:
Bitmap image editors convert vector-based drawings to bitmaps by rasterizing
(Photoshop does this automatically)
BY: DR. ZEESHAN BHATTI 11
GRAPHIC/IMAGE DATA
This section introduces some of the most common graphics and image file formats. Some of them are restricted to particular hardware/operating system platforms, others are cross-platform independent formats.
While not all formats are cross-platform, there are conversion applications that will recognize and translate formats from other systems.
Most image formats incorporate some variation of a compression technique due to the large storage size of image files. Compression techniques can be classified into either lossless or lossy.
BY: DR. ZEESHAN BHATTI 12
RESOLUTION
Two termsDPI and PPI
Screen resolutionFixed resolution (nearly) PAL, NTSC, VGA, SVGA 72dpi, 96dpi
Print / Scan resolutionUser definableSize variablePhysical dimension = pixel dimension/device resolution
BY: DR. ZEESHAN BHATTI 13
IMAGE RESOLUTION:
Image resolution refers to the number of pixels per inch area of an image.
• Higher the resolution, means higher the number of pixels in that image hence better the quality but also with increase in file size.
• Lower the resolution means less amount of pixels in an image and hence having poor quality with less file size.
BY: DR. ZEESHAN BHATTI 14
ASPECT RATIO
Aspect Ratio means the ratio of file’s Width to its Height. For example
640 x 480 or 800 x 600 or 1024 x 768
• These number define the Width and height of an image but with a specific aspect ratio of 4:3
• all Monitors and Display systems fallow a particular aspect ratio i.e. 4:3, to display contents.
• This 4:3 aspect ratio has been found to look natural on Monitors and other display systems.
BY: DR. ZEESHAN BHATTI 15
GRAPHIC/IMAGE DATA STRUCTURES A digital image consists of many picture elements, termed pixels. The number of pixels that compose a monitor image determine the quality of the image (resolution). Higher resolution always yields better quality. A bit-map representation stores the graphic/image data in the same manner that the computer monitor contents are stored in video memory
1.Monochrome/ 1-Bit Images
2.8-bit Gray-scale Images
3.8-bit Colour Images
4.24-bit Colour Images
5.32-bit Colour Images
BY: DR. ZEESHAN BHATTI 16
IMAGE DATA TYPES
•The most common data types for graphics and image file formats are 24-bit color and 8-bit color.
•Some formats are restricted to particular hardware/operating system platforms, while others are \cross-platform" formats.
•Even if some formats are not cross-platform, there are conversion applications that will recognize and translate formats from one system to another.
•Most image formats incorporate some variation of a compression technique due to the large storage size of image files. Compression techniques can be classified into either lossless or lossy.
BY: DR. ZEESHAN BHATTI 17
MONOCHROME/ 1-BIT IMAGES An example of 1-bit monochrome image is illustrated in Fig. 3.4 where:
• Image consists of Pixels or Pel (Picture Element).
• A 1-bit image consists of on and off bits only and thus is the simplest type of image.
• Each pixel is stored as a single bit (0 or 1), or we can say that each pixel occupies exactly 1- Bit in memory.
• Hence it is also referred to as a binary image.
• Monochrome 1-bit images can be satisfactory for pictures containg onlysimple graphics and text.
BY: DR. ZEESHAN BHATTI 18
Figure 3.4: Sample Monochrome Bit-Map Image
BY: DR. ZEESHAN BHATTI 19
8-BIT GRAY-SCALE IMAGES An example gray-scale image is illustrated in Fig. 3.5
where:
• Each pixel is usually stored as a byte, occupying 8-bits in memory.
• Each pixel has a grayscale value between 0 to 255, where 0 is for Black and 255 is used for White colors, as shown in figure 3.5a.
• The Entire image can be thought of as a two-dimensional array of pixel values. We refer to such an array as a bitmap.
• A 640 x 480 greyscale image requires over 300 KB of storage, as shown in figure 3.5.
A Gray scale color representationBY: DR. ZEESHAN BHATTI 20
We can think of the 8-bit images as a set of 1-bit bitplanes, where each plane consistes of a 1-bit representation of the image at higher and higher level of “elevation”: a bit is turned on if the image pixel has a nonzero value at or above that bit level.
Figure 3.6b displays the concept of bitplanes graphically. Each bit-plane can have a value of 0 or 1 at each pixel but together, all the bitplanes make up a single byte that stores values between 0 and 255 (in this 8-bit situation)
Bitplanes for 8-bit gray scale image
Example of a Gray-scale Bit-map Image
BY: DR. ZEESHAN BHATTI 21
8-BIT COLOUR IMAGES
An example 8-bit colour image is illustrated in Fig.3.6 where:
• One byte for each pixel
• Supports 256 out of the millions s possible, acceptable colour quality
• Requires Colour Look-Up Tables (LUTs)
• A 640 x 480 8-bit colour image requires 307.2 KB of storage (the same as 8-bit greyscale)
BY: DR. ZEESHAN BHATTI 22
COLOR LOOKUP TABLE(LUTS OR CLUTS)
The idea used in 8-bit color images is to store the index, or code value, for each pixel. Then, if a pixel stores, say, the value 25, the meaning is to go to row 25 in a color lookup table (LUT).
For an 8-bit image, the image file can store in the file header information just what 8 bit values for R, G, and B correspond to each index. Figure 3.8 displays this idea.
The LUT is often called palette
Example of 8-Bit Colour ImageBY: DR. ZEESHAN BHATTI 23
Basically, the image stores not color, but instead just a set of bytes, each of which is actually an index into a table with 3-byte values that specify the color for a pixel with that lookup table index.
BY: DR. ZEESHAN BHATTI 24
COLOR-PICKER
A Color-picker consists of an array of fairly large blocks of color (or a semi-continuous range of colors) such that a mouse-click will select the color indicated. In reality, a color-picker displays the palette colors associated with index values from 0 to 255.
Fig. 3.9 displays the concept of a color-picker: if the user selects the color block with index value 2, then the color meant is cyan, with RGB values (0; 255; 255).
A very simple animation process is possible via simply changing the color table: this is called color cycling or palette animation.
BY: DR. ZEESHAN BHATTI 25
BY: DR. ZEESHAN BHATTI 26
24-BIT COLOUR IMAGES An example 24-bit colour image is illustrated in Fig. 6.14 where:
• Each pixel is represented by 24-bit (three bytes).Each byte is for separate color channel i.e. RGB.
•1 byte for Red has 255 shades of Red to White and similarly for other Green and Blue color.
• Supports 256 x 256 x 256 possible combined colours (16,777,216)
• A 640 x 480 24-bit colour image would require 921.6 KB of storage
•
BY: DR. ZEESHAN BHATTI 27
Fig. 3.5 shows the image forestre.bmp., a 24-bit image in Microsoft Windows BMP format. Also shown are the grayscale images for just the Red, Green, and Blue channels, for this image.
BY: DR. ZEESHAN BHATTI 28
32-BIT COLOUR IMAGES
Most 24-bit images are 32-bit images, the extra byte of data for each pixel is used to store an alpha value representing special effect information
BY: DR. ZEESHAN BHATTI 29
THANKYOU
Q & A
BY: DR. ZEESHAN BHATTI 30
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