Gif Viewer 2.0  by David Jansen

Option "A" displays the disk directory of the current device.  Press any key
return to the main menu, press stop to abort.

Option "B" sets the current device.  The device number can range from 8-11.

Option "C" determines the graphic mode used when drawing a GIF, and also the
file format to be used when saving an image (see option "H" below).  When this
option is "Yes" the GIF is drawn in hi-res multi-color mode.  When "No"
standard hi-res mode is used.

Option "D" applies to multi-color mode only and determines the screen width.
The physical screen size in multi-color hi-res mode is 160 x 200.  This option
should normally be set to 160 so that it matches the screen display.  You can,
however, set it to 320.  This will cause greater distortion of the image
because you will be drawing a 320 pixel width on a 160 pixel wide screen.  The
advantage of this is you see more of the image on screen.

Option "E" allows you to scroll the viewing window left or right.  The value
here determines the horizontal starting position.  The horizontal viewing range
is:  value of option "E" to value of option "E" + screen width - 1

Option "F" allows you to scroll the viewing window up or down.  The value here
determines the vertical starting position.  The vertical viewing range is:
value of option "F" to value of option "F" + 199

Option "G" allows you to use gray scaling.  When this option is set to "Yes"
all colors will be translated to a shade of gray.  While this mode strips the
color from an image you will find that it often produces the best results.

Option "H" allows you to save the previously viewed GIF.  Before using this
option you must first view a GIF (it must be viewed completely for the save to
work correctly).  Then select this option.  The save format is determined by
the hi-res mode you used to view the GIF.  If option "C" is "yes" the save will
be in Koala format.  If option "C" is "no" the save will be in Doodle format.
It is your responsibility to provide proper names (use "DD" as the first 2
characters in Doodle names.  For Koala use a temporary name and rename it later
with the "pic" prefix).

Option "I" allows you to view a GIF.

Option "J" allows you to exit to BASIC.



Notes:

    Windows are an important concept.  By changing the viewing window you can
view virtually any part of a GIF.  If you set the window values to a range
outside of the GIF image's range you will get a blank screen.  I suggest using
either hi-res or multi-color hi-res with a width of 320, and set both window
values to zero the first time you view a GIF.  When you get an idea of how the
image appears you can move the window to the area you wish to view more
accurately.  The best results are usually found in multi-color hi-res mode with
a width of 160.  Gray scaling oftens increases the quality.  Experiment until
you feel comfortable with these features.

If you ever come across a GIF that was created from a C64 graphic you should
always set your window values to a multiple of 8 so that you don't get
"framing" errors.  To illustrate this point I have included a GIF
("midearth.gif") that I created from the Doodle file "ddmiddle earth."  To view
this file set option "C" to "no" so that you are in hi-res mode, and set your
window values to zero.  Then view the file.  If you did it correctly you will
see a replica of "ddmiddle earth."  Now set the "Window X" value to 1.  View it
again and you will see "framing" errors.  You will find that window values that
are multiples of 8 will work correctly, but other values corrupt color.  The
reason has to do with the way the C64 displays color.  In hi-res mode each 8 x
8 matrix of pixels can display 2 colors.  Suppose this is the upper 16 x 8
pixels in the image:

bbbbbbbb yyyyyyyy
gggggggg yyyyyyyy
bgbgbgbg ybybybyb        Note that each 8 x 8 area has at most 2 colors
bbbbbbbb yyyyyyyy        The first has blue & green, the second has
bbbbbbbb yyyyyyyy        yellow and blue.
bbbbbbbb yyyyyyyy
bbbbbbbb yyyyyyyy
bbbbbbbb yyyyyyyy

b=blue g=green y=yellow


With Window X equal to 1 you effective shift the picture 1 pixel left.  You the
get:

bbbbbbby yyyyyyy?
gggggggy yyyyyyy?        Each pixel was shifted 1 to the left.  The "?"
gbgbgbgy bybybyb?        represent the leftmost pixels from the third
bbbbbbby yyyyyyy?        8 x 8 matrix (not shown in this example).
bbbbbbby yyyyyyy?        The leftmost 8 x 8 matrix now has 3 colors in it,
bbbbbbby yyyyyyy?        blue, green, and yellow.  The C64 cannot put 3
bbbbbbby yyyyyyy?        colors in this area, and this causes a color
bbbbbbby yyyyyyy?        conflict.


This framing error occurs most notably in C64 format GIF's.