NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/sys/amiga/programmer/5530

Text File | 1996-08-05 | 9.1 KB | 174 lines

Path: uu4news.netcom.com!genesplicer!209-254-8!joey.mcdonald
From: [e-mail] (Joey McDonald)
Date: 15 Mar 96 10:49:09
Newsgroups: comp.sys.amiga.programmer
Subject: DCTVpost 2/5
Message-ID: <[e-mail]>
Organization: The GeneSplicer

Chapter1:
                       BREAKTHROUGH DCTV DISPLAY MODE!

                              By Joey McDonald
                              ⌐ copyright 1996



Roughly 5 years after its introduction DCTV remains a popular Amiga display
board and a viable alternative to 24-bit display devices. Portability,
compatibility with all Amiga systems and the ability to play high speed million
color animations are just a few of the features that have contributed to ts
long lasting popularity. Within the last 5 years there have been many other
improvements in Amiga display technology. The introduction of AGA chips and
24-bit display devices offering "programmable" resolutions may have left many
DCTV owners feeling a bit limited by there rather sparse selection f display
mode options. In an attempt to add more variety (and excitement) to the
Amiga/DCTV display arsenal, this article will introduce a NEW DCTV display mode
that will allow faster animations and greatly reduce file sizes. Dust off your
DCTV and get ready to Rock'n Roll!


DCTV constructs its composite video output from special screen data contained
in an Amiga hi-res, 3 or 4 bitplane display. The 4-bit mode delivers the
highest possible display quality, while the 3-bit mode sacrifices a small
amount of image detail to produce smaller file sizes and animations that ply at
a higher frame rate. Since there are no software options for a 1 or 2 bitplane
display mode you may have assumed that DCTV requires at least an Amiga
3-bitplane display to function properly. You're in for a pleasant surprise. I
have discovered that DCTV is quite capable of functioning in an Amia 2-bit mode
while retaining most of its composite color palette and display quality. Since
the 2-bit mode is not supported in any way by the software, it's currently
impossible to directly create a 2-bit DCTV image. To demonstrate the potential
of the 2-bit mode we will need to use a separate progrm to convert a previously
created image. What follows is an explanation of the conversion process in the
form of a mini-tutorial.

For this exercise you'll need DCTV disk#3 (included with DCTV) and the image
processor Pixmate. I have not found another image processor capable of
generating the required results. It's pointless to use a program that first
converts an image into 24-bits (ADPro, ImageMaster) since DCTV only needs upto
4-bits to comprise an image. It's also important to note that the Pixmate
program has been discontinued. All descriptions of screens and controls are
representative of version 1.1.

Before we begin make sure your DCTV is connected, we'll want to view how our
actions within Pixmate effect the composite image. When a Pixmate control
window opens on the image it may distort or block the composite display.
Holding the right mouse button down will temporarily remove the window allowng
you to view your progress. A two monitor set-up is ideal, but a single monitor
with RGB switching (such as the 1084s) will suffice.

I will describe the conversion process in two major steps. We'll start by
converting the image into its 2-bit form, and then rap things up by making a
few necessary color adjustments. After we have finished this tutorial I'll
discuss the reasons some images do not convert well and further possibilites
for this new display mode. Let's go!


                         STEP #1: BITPLANE BUSTING.


Start Pixmate and then load the picture named froggie.dctv (found in the images
drawer on DCTV disk #3). DCTV will not detect or display a composite image
while the Pixmate menu bar is active. Disable the menu bar by selecting the
"toggle title" item from the EDIT menu. The froggie.dctv image shouldnow appear
in all of its composite glory. (figure 1.)

Choose the DISPLAY item from the "effects" menu to open the display control
panel. Looking at the gadgets that represent image bitplanes you'll notice that
number's 1 through 4 are highlighted (indicating that we're working with a 4
bitplane image). When working with a 4 bitplane DCTV image you willalways want
to discard plane numbers 1 and 2 (only plane number 1 for 3-bitplane images).
We can't actually remove the planes at this time, so we will temporarily render
them inactive. De-select the number 1 and 2 gadgets and then close the display
window to exit back to the main screen. Our composie image should exhibit a
noticeable loss of color and a small reduction in detail.

Next, go to the "color" menu and select the PACK COLORS item. Pixmate will then
process the RGB image and re-map the palette. This process does not generate a
viewable difference in the composite image, but it's a required step before
performing any further actions. You can also use the LESS COLORS tem from the
"color" menu to achieve the same results (by inputting a "4" for the number of
colors to use) but the process is slower than simply selecting PACK COLORS.

Once again choose the DISPLAY item from the "effects" menu to open the display
control panel. The bitplane gadgets will again indicate that we're working with
a 4-bitplane image. This time de-select plane numbers 3 and 4 (you should not
see a change in the image) and then select the REFORM gadget. Arequester will
pop up informing you that "image bitmap change will permanently discard some
bitplanes, reducing the number of colors." Since we have already processed and
re-mapped the appropriate colors, we have nothing to lose by continuing. Select
CHOP PLANES to remove the unwanted bitplanes and ransform our picture into a
2-bit image (figure 2).

Now that we have chopped the unwanted planes and reduced the number of colors,
it's time to proceed to step #2 and do some tricky tweaking (say that 5 times,
fast) of our images' palette.


                            STEP #2: PALETTE MAGIC.


Our newly converted 2-bit image has little or no color and an annoying flicker.
Correcting the image is a fairly easy and straight forward process. Let's get
to it.

There are two different methods we can use to achieve the results we desire.
The first method offers fairly precise control over color correction, while the
second method offers less control but is an easier and faster process to
perform. Both are capable of excellent (and practically identical) reslts.

Method  #1:

Select the "palette" item from the COLOR menu. A small window will appear
containing a somewhat standard Amiga palette adjuster. You'll see the familiar
RGB sliders and color value information.

Before we begin adjusting color levels, it's important for you to remember that
we're working with a DCTV image. The palette controls will effect our composite
display in a vastly different way than an ordinary RGB display. Also, because
of small differences between certain DCTV equipped Amiga systes the color
values given below may be slightly different from those required on your
system. If you experience problems, experiment to find the most effective
values.

For this image (and the majority of images you will convert) only the
blue-levels for each color need to be adjusted. We will start with the last
color on the right (color 3) and work left to color 0. I have listed all 4
setting adjustments below as steps A through D.

A. Select color 3 and use the blue-level adjuster to increase the color value
to a setting of 87F (all the way to the right). Checking your composite display
you should immediately notice a considerable improvement in image color.

B. Select color 2 and increase the blue-levels to a value of 87E. You should
notice a massive improvement in the composite image.

C. Choose color 1 and increase the blue-levels to a value of 00F (again, all
the way to the right). You may not see a dramatic change in the composite
image, but there is an improvement. (Sliding the adjuster back and forth to
different values will give you an idea of how this setting effects the diplay).

D. Some areas of the image will still contain small horizontal lines (most
visible on the eye of froggie). Select color 0 and increase the blue-levels to
a value of 00E. You should notice a subtle "color-smoothing" effect which
reduces horizontal lines leaving our final image (figure 3) closely resebling
its original 4-bit quality. Welcome to the wonderful world of million color
2-bit DCTV images!

Before we celebrate our successful conversion and rap up the tutorial, I'll
quickly demonstrate the second method of correcting image color and detail. You
may wish to save this image before we proceed in order to compare the separate
results.

Method #2:

If you still have the palette window open, close it to return to the main
screen. Select "undo changes" from the EDIT menu to return our image to its
"pre-color-corrected" appearance.

Choose The "color bias" option from the COLOR menu. A window will appear
offering a variety of image enhancement controls. Unlike the RGB sliders
offered by the palette window, these controls effect the entire range of
colors, not just one specific color at a time.