Tracy Marks' Photoshop exercises
Photoshop for Web Design

Index of online assignments:
Lesson Two   Creating banners
Lesson Three   JPG quality
Lesson Four  Gif and JPG

Lesson 2

1. Create a page banner from scratch using browser-safe colors.

I created windbann.gif using the web palette. The size is 3.9kb.

As an experiment, I converted to RGB, then back to indexed color using the
exact palette for 27 colors. The size reduced to 3.18kb. Isn't this an advantage?
This is windban2.gif.

2. Find or create a small-photograph-style image. Convert it to Indexed
Color using both web and adaptive options, with and without dithering.

This is the original photo of
Princess Diana - dianpink.jpg
The size is 14.3kb.


     LEFT dianwebn.gif,
    12kb, web palette,
     without dithering.

     RIGHT dianwebd.gif,
    18kb, web palette
     with dithering. 


     LEFT dianadnd.gif,
     25kb, adaptive palette,
     without dithering.

     RIGHT dianadd.gif,
     28kb, adaptive palette
     with dithering. 

The largest file was adaptive palette dithered. The smallest was web palette,
nondithered. Dithering seems to add to file size, and the adaptive palette
makes for larger files than the web palette.

The worst picture is web palette, nondithered. Patches of bright pink
and gold severely deteriorated the photograph. Web palette dithered
is definitely a significant improvement, but full of speckles. This
image is not acceptable either. The web palette does not seem to be
able to capture the subtleties and gradations of skin tones.

The gif files, adaptive palette are definitely better than the web palette,
but still inferior to the original jpg file. At first glance, the dithered
and nondithered pictures appear similar...but the dithered image has
speckles of unwanted color and the nondithered image has slabs of
unwanted color. For some reason, the dithered image also appears
wider, as if it has more breadth and depth.

If I had to use one of the gif files, I would choose the 25kb adaptive
palette nondithered, but the 15kb jpg file is preferable.

Tracy Marks

Other Photoshop Lessons for Zdnet Class:
pshop3.htm       pshop4a.htm      pshop4b.htm