Images in INTKEY

Mike Dallwitz miked at ENTO.CSIRO.AU
Fri Aug 12 11:22:36 CDT 1994


                                                                 12 August 1994



I have sent this reply to the list because it may be of general interest.

> Subject: HELP: displaying images in INTKEY
>
> Images get out of shape when they are displayed on the screen. They are 480
> pixels high. What do I have to do?
>
> From: Theo Pannen <t.pannen at PEGASUS.PING.DE>

There are two possible causes.

(1) When the MS-DOS version of INTKEY displays an image, it sets the lowest-
resolution and lowest-colour graphics mode that will accommodate the image. One
of the 256-colour modes on a standard VGA card has a resolution of 360x480
pixels. Because the aspect ratio of a screen is 4:3, the pixels in this mode
are rectangular rather than square. Early versions of INTKEY selected this mode
for any 256-colour image with dimensions less than or equal to 360x480. If the
image was intended for display with square pixels, it would be stretched
horizontally when displayed in this mode. The solution was to avoid images with
such dimensions (easily done by filling images with blank space to 640x480).
However, we decided that display modes below 640x480 were not really useful,
and they were excluded from Version 3.08, 17 November 1993 (see CHANGES.1ST).
Thus, this is no longer a problem in the current version (3.13). The MS-Windows
version of INTKEY, soon to be released, has scaling and scrolling of images, so
images of any size can be displayed.

(2) Many monitors do not automatically maintain the aspect ratio of the display
area when the display mode is changed - manual controls must be used. Better-
quality monitors can save the appropriate settings for each mode, and restore
them automatically when the mode changes. This problem is alleviated when using
MS-Windows, as Windows applications do not change the display mode (changing
the mode requires restarting Windows). However, running full-screen DOS
sessions from Windows still causes a mode change.

Although the Windows INTKEY will display any image while running in standard
VGA mode, the quality will generally be sub-optimal for all except black-and-
white images. This is because Windows uses a fixed palette of 16 colours in
this mode (and in other 16 colour modes); that is, the palette is not optimized
for the display of any given image. (Also, the quality of black-and-white
images is intrisically poor in low-resolution modes; we recommend the use of 16
grey levels for line drawings.)

For good performance and image quality, we recommend a local-bus Super VGA
display card with Windows accelerator and at least 32768 colours at 800x600 or
1024x768 resolution. The display should be non-interlaced. When evaluating a
card and monitor, ask to see Windows running in non-interlaced mode with the
number of colours and resolution that you require. An interlaced display
shimmers, and narrow, dark lines appear to separate the horizontal scan lines.
Sales people are often unaware that special actions may be necessary to make a
card work in non-interlaced mode at high resolutions. Simply using Windows
Setup to change from a low-resolution to a high-resolution mode may result in
the use of an interlaced mode, even though a non-interlaced mode of the same
resolution is available on the card.

Software for editing bitmap images makes heavy demands on memory and processing
power, and images can require large amounts of disk space. So if you are
preparing images (not just viewing them), the following configuration is
suggested as the minimum desirable on IBM-compatible PC's. Motherboard with 486
66MHz CPU and local bus (VESA or similar), 16MB RAM, local-bus Super VGA
display card with Windows accelerator and at least 32768 colours at 800x600
(including Windows drivers), high-resolution monitor (equivalent to NEC 5FG or
better), 400 MB hard disk. A high-speed, high-capacity tape drive is also very
desirable. DDS (DAT) tapes have a capacity of 2GB, and are small and cheap,
although the drives are fairly expensive - currently about AU$1500. Compatible
drives are made by several manufacturers.

Mike Dallwitz                                  Internet md at ento.csiro.au
CSIRO Division of Entomology                   Fax +61 6 246 4000
GPO Box 1700, Canberra ACT 2601, Australia     Phone +61 6 246 4075




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