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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 its 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 of
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
play 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 Amiga 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 program 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 up
to 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
allowing 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 possibilities
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
should now 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 will
always 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
composite 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
item 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.
A requester 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 transform 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) results.

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
systems 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
display).

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
resembling 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