1. 6th Lecture – Rectangles and Regions, and intro to Bitmap Images
CPT 450 Computer Graphics
6th Lecture – Rectangles and Regions, and intro to Bitmap Images

2. Rectangles
The Rectangle structure stores the top left starting point (x, y) and the width and height.
The Rectangle can be constructed with
new Rectangle (point, size) or
new Rectangle (x, y, w, h)
Notes:
A (2D) point object contains an x and y coordinate
A size object contains a width and height.
There are integer and a floating point (single precision) versions of these objects. The floating point versions end in the letter F.

3. More on Rectangles
It has methods to return the left, top, right, and bottom coordinates.
Where
Left = x
Top = y
Right = x + w
Bottom = y + h
Also has round, truncate, inflate, ceiling, intersect and union methods.
The “contains” method can be used to test if the user clicks inside a rectangle, i.e.
left < point.x < right AND top < point.y < bottom

4. Region Class
A region describes the interior of a closed graphics shape or form.
A form has 2 regions
Client area, the area where the user can draw
Non client area, such as the title bar, the scroll bars, etc..
Contructor has overloaded versions which take rectangles, graphicsPath or region data.
No properties
The graphics object g has a fill method, i.e. g.fillRegion to shade the region

5. Region Methods Many methods. See documentation. For combining regions,
Compliment
Exclude
Union
Intersect
Xor
Regions can be used for clipping.
Author’s sample creates non-rectangular forms. (used by Music/Video players)

6. Graphics Path
You can combine many vector drawing methods into a graphics path. Then you can use the path to draw a shape.
Example If you draw lots of a particular pattern in your program, then you can create a graphics path and use it to draw each shape (like a subroutine).

7. Intro to Bitmap or Raster Images

8. What is the difference between bitmap and vector graphics?
A bitmap or raster image is a collection of pixels (picture element), each with it’s own independent color.
A vector image is made up of vector graphics instructions such as drawLine or drawEllipse.
Converting from one type to another
From vector to raster – this is called scan conversion
From raster to vector – this is called pattern recognition or OCR

9. Where do they come from? Digital Cameras (now in cell phones)
Optical Scanners
Video
Fax
Medical Imaging (X-ray, CAT Scan, MRI)
Satellite data
Generated by scan converting vector graphics instructions
Internet (google)

10. How are bitmap or raster images stored?
Generally, the images are rectangular and can be represented in matrix form (row, column), as a table of colors.
In the file, they are store sequentially. Could be either
(row, column) or (column, row)
In the old days, the pixels on the screen were directly mapped to the video memory, hence the word “map”.
Video memory could be addressed directly by the programmer. This was fast and convenient but very dangerous.
The image files can contain a header and footer. This can contain the width and height of the image, the color depth, and other info about the image.

11. Some Image File formats
File types
File extensions
Bitmap
bmp
Icon
Ico
Cursor
cur
Windows meta file
wmf
GIF
gif
JPEG
jpg or jpeg
TIFF
tif or tiff

12. Grayscale images
Gray scale images only require 1 intensity per pixel (remember R=G=B), instead of 3 for color (excluding transparency)
8 bits/pixel can display 256 shades of gray.
1 bit/pixel can display only two shades, black or white
Using dithering, newpapers can create shades of grade, by varying the size of the dots in the picture.

13. Dithering
Dithering – used to create the appearance of a new color by combining different sized dots of different colors. See the comics in the Sunday newspaper!

14. The Art of Roy Lichtenstein (an example of dithering)