Graphic Images

Tom Kelliher, CS 102

Oct. 21, 1998

Announcements:

Start homepage, quiz on Friday.

From last time:

1. Paint Shop Pro

Outline:

1. Paint Shop Pro, images and scanning.

Assignment:

Readings:

1. A Few Scanning Tips (http://www.scantips.com/basics01.html)

2. Preparing Graphics for the Web
   (http://www.servtech.com/~dougg/graphics/index.html)

Things to Know about Paint Shop Pro

1. Selecting foreground/background colors.

2. GIF format: 87a/89a, interlacing, transparency.

3. JPEG format: compression.

4. Images menu: resample, special effects (buttonize), filters (emboss). What to do when they're grayed out.

5. Colors menu: adjust (brightness/contrast), grayscale, decrease/increase color depth.

6. Selections: select none.

7. Tools: zoom, selection, dropper, brushes, air brush, flood fill, text, line, shape.

Images and Scanning

Introduction:

1. Pixels --- what are they in a file? Number containing a color value:
   1. 8 bit byte: 256 colors from a palette of 256, 64K, 16M?

   2. 3 bytes: 256 intensity levels for red, green blue. Triplet: (r, g, b). Black: (0, 0, 0). White: (255, 255, 255). Pure red: (255, 0, 0).

2. Image size varies with scanned DPI.

3. GIF file format:
   1. Dimensions of image.

   2. Color palette: 2--256 choices from 16M.

   3. Pixel data: 1--8 bits (2--256 colors) per pixel

   4. Lossless Compression.

4. JPEG: lossy compression, image converted to chrominance and luminance information.

5. Which to use when:
   1. GIF: images with sharp edges and flat colors. Icons, buttons, text.

   2. JPEG: photos, naturalistic images. Set compression to about 50%.

   3. Tradeoff: image quality vs. file size.

6. Graphic image size = .

7. Viewer considerations:

   

8. Preferable to overscan and resample down in PSP rather than resample up. Why?

9. Relationship between image size and memory required: