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Unit 11: Graphics

as create charts on the fly, create an anti-robot security image, create thumbnail images, Notes
or even build images from other images.
• GD has an existing API, and PHP tries to follows its syntax and function-naming
conventions. So, if you are familiar with GD from other languages, such as C or Perl, you
can easily use GD with PHP.
• PHP cleans up the image when the script ends, but, if you wish to manually deallocate
the memory used by the image, calling ImageDestroy($image)forces PHP to get rid of
the image immediately.

• The standard rectangular or Cartesian (named after René Descartes) has two perpendicular
real number lines (axes) which divide the plane into four quadrants. The place where the
number lines cross is the origin (0, 0) and the numbering is positive to the right and up;
negative to the left and down.
• One of the most basic features of computers today is the ability to edit graphics. Many
times, you need to build web applications that take image data from users and scale it
down to a format that can easily be displayed on your website.
• Colour support improved markedly between GD 1.x and GD 2.x. In GD 1.x there was no
notion of the alpha channel, colour handling was rather simple, and the library supported
only 8-bit palette images (256 colours).

• An interesting use of the ImageColorAt( ) function is to loop through each pixel in an
image and check the colour, and then do something with that colour data.

11.10 Keywords

.bmp: (pronounced “bimp”) this is a “bitmap.” You will probably never place a bitmap as an
image, although some browsers do allow it. A bitmap is an image that a computer produces
and places for you. For example counter.
.jpeg or .jpg: (pronounced “j-peg”) there are two names to denote this format because of the PC
and MAC formats allowing 3 and 4 letters after the dot. JPEG is an acronym for Joint Photographic
Experts Group, the organization that invented the format.

.png: Pronounced as ‘ping’, this stands for Portable Network Graphic. This is ultimately the
replacement for .gif, with partial transparency options, but browser support is sketchy—some
browsers still do not like to display .png files.
Alpha blending: Alpha blending is a toggle that determines whether the alpha channel, if present,
should be applied when drawing. If alpha blending is off, the old pixel is replaced with the new
pixel. If an alpha channel exists for the new pixel, it is maintained, but all pixel information for
the original pixel being overwritten is lost.
ALT: It stands for “alternate text”. This tells the browser that if it cannot find the image, then
just displays this text. It also tells anyone who cannot view your image what the image is about.
Antialiasing: Antialiasing is where pixels at the edge of a shape are moved or recoloured to
make a gradual transition between the shape and its background. This prevents the rough and
jagged edges that can make for unappealing images.

Gif: This is pronounced “jif” or “gif” (hard “G”) depending on whom you speak to. “jif”, like
the peanut butter. This is an acronym for Graphics Interchange Format.
HEIGHT: It stands for, as you might guess, the height of the image in pixels. Again, the height
can be just about anything, but generally will be less than the height of the web browser.

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