Glossary

A way of making jagged lines appear smoother by filling the edges with colors that are averaged between the line color and background color. Similar to a blurring effect.

Blur

A type of filter that softens an image, making it looked blurred. A gaussian average can be used to reduce detail and create a hazy effect.

Clipboard

Copying an image takes that information and writes it into a portion of RAM, called the clipboard, that serves as temporary storage. Pasting the image transfers it back into a document. Most of the time it has to be in the same application, though sometimes information (like text) can be transferred, using the clipboard, from one application to another.

Color

8, 16 or 32 bit color, which is equal to 256, thousands of colors and millions of colors respectively. 8 bit color can be called Index color because it uses a specific palette of only 256 colors. 16 and 32 bit color is commonly called RGB (red-green-blue) color. File types like GIF, Pixelpaint and Macpaint can only be 8 bit color, while other file types like JPEG and TIFF are all inclusive.

Crop

Using a tool (as in Photoshop or other painting program) to draw a line around the area of an image that you want, and "cropping" by clicking inside of the area. This procedure varies from program to program, but most of them have an option to adjust the canvas size or area of the image, which has the same effect.

DPI

Dots(pixels) per inch - the number of pixels per inch in an image. The more pixels there are per inch, the higher the resolution of the image will be. If this is changed proportionally with the size (e.g. increase size/decrease dpi) then there is no change in quality. If this is changed independent of the size, then there is a change in quality.

Grayscale

8 bit black and white, where there is a progression from black to white with 254 grays in between. Gets very good results from LZW and JPEG Compression. Grayscale images can be converted to 1 bit line art using a pattern dither, a random dither or a 50% threshold.

HSB

Hue-Saturation-Brightness. The hue is the color, saturation is the presence or lack of white and brightness is the presence or lack of black.

JPEG

Joint Photographer's Expert's Group - a type of compression that minimizes the amount of color information in your image that is actually not distinguishable. JPEG compression rates can be very high, although using it too many times on the same image will result in a loss of quality.

Line Art

1 bit black and white (bitmapped), where there are only two colors possible in your image. Normal line art may consist of a diagram or line drawing.

LZW Compression

A type of compression that can be used automatically when saving TIFF files. Using LZW compression will not result in a loss in quality, but the compression rate decreases as the amount of information (number of bits) increases - very good for line art images.

Sharpen

A type of filter that finds changes in color and contrast and makes them more defined.

BACK Return to the Webimages homepage

BACK Return to the Webclass homepage

Last revision July 11, 1995

An example of using JPEG compression on the same file four times and the composite result.

An example of different types of dithering schemes for conversion to 2 bit black and white
(clockwise from upper left: grayscale original, 50% threshold, random dither, pattern dither).

An example of different types of dithering schemes for conversion to 8 bit Indexed color
(clockwise from upper left: color original, adaptive palette / no dither, adaptive palette / diffusion dither, system palette / diffusion dither).