HOW VENTURA WINDOWS EDITION 4.0 DISPLAYS GRAY_SCALE IMAGES

The ability for Ventura Publisher 4.0 to display gray-scale is a function
of the video driver, not the video card itself. When a gray-scale image is
loaded into Ventura, Ventura opens the Windows color palette and attempts
to locate three shades of gray in addition to black and white. If these
three shade of gray are available, the image will appear on the screen as
gray-scale. If the three shades of gray are not available, the image will
appear dithered. It is important to not that, regardless of how the image
appears on the screen, the image will print according the settings in the
Image Settings dialog box.

Now, how does the video driver come into play. Well, video drivers
controls how the colors are displayed in Windows. The video driver, in
order to display a color, will do one of three things. 

1). The driver will us the Windows color palette, without modification.
This palette contains 20 colors. With video cards that supply 256 or more
colors, this palette must be modified or substituted.

2). The video driver will dither the Windows palette in order to provide
more colors. This is the most typical option used by 256-color video
drivers, but since the default Windows palette does not provide 3 shades
of gray, not will the dithered palette.

3). The video driver supplies and substitutes a color palette of its own.
How this palette is supplied and what colors it conatins are entirly up to
the peaople who write the video driver. This type of driver is used by the
32K/65K-color (15/16-bit) and 16M-color (24-bit) video cards, as well as
SOME 256-color video cards.

For 256-color video drivers, dithering the default Windows color palette
provides the best performance as far as display speed.

The question has also comes up about why other Windows applcations will
display gray-scale while Ventura will not. A Windows application also has
the ability to create and substitute a color palette. A good exaple of
this would be Zsofts Publisher's Paintbrush. When a gray-scale image is
loaded into Publisher's Paintbrush, the application will create a palette
(in this case, of grays) and substitute the Windows palette for the
created one. This is what cause the screen (and all Windows icons and
such) to turn gray.

The performance "hit" taken by this type of application is rather small
since it usually deals with one or a small number of pictures (and
palettes). On the other hand, Ventura is designed to handle a large
number of images (128) in a single chapter. Creating palettes for each of
these images (both gray-scale and color) would cause a tremendous
performance hit to Ventura. In addition, there would be an additional
performance hit caused by the mechinism that would be required to
determine which palette to use when more than one image is displayed
on the screen in Ventura.

Typically (and we are still compiling information on this), drivers that
are 8514 compatible will provide the required palette.
Also, gray-scale, 32k, 65k, and 16m color drivers will provide the
required palette.

Hope this helps clear up any gray area
Kevin K.
VSI