L O O K E R I m a g e P r o c e s s o r Copyright 1987 by Frederick Hawkins
LOOKER may be freely distributed as long as this document accompanies it.
________ Q U I C K R E F E R E N C E __________________________________
File
L LOAD .PI1, .PI3, .DTH
S SAVE .PI3, .DTH
Palette
[Clr Home] START a new palette list.
[Insert] ADD to a palette list.
[Undo] DISCARD palette list.
[Up,Down] SELECT a color to change.
[Right] LIGHTEN the halftone of a palette color or palette list.
[Left] DARKEN the halftone.
[1 to 9] Set INCREMENT used by Lighten and Darken.
N Show a NEGATIVE view of a color.
R RESET palette to default values.
Z ZERO all other palette values.
Transform
A Show ALTERNATIVE settings.
C COPY current settings to ALTERNATE.
D DITHER.
G GRAY.
H HALFTONE.
T Change Dither TYPE.
X MEZZOTINT.
[0 zero] Perform TRANSFORM.
Buffers
[cr] Toggle between MAIN and WORK.
K View KEEP buffer.
[*] ERASE Keep buffer.
[+] SET Keep with Work buffer.
[-] CLEAR Keep with Work buffer.
[/] STRIKE last Keep buffer change.
System
[#] Load TEST pattern.
[Help] HELP.
I INSTALL or change Dither tables.
Q QUIT.
M MAGNIFY.
V VERSION.
[&] Trap to SID.
________C O M M A N D S alphabetical_________________________________
[Clr Home] START a new palette list. Palette
[Help] HELP. System
[Insert] ADD to a palette list. Palette
[Left] DARKEN the halftone. Palette
[Right] LIGHTEN a color or list. Palette
[Undo] DISCARD palette list. Palette
[Up,Down] SELECT a color to change. Palette
[/] STRIKE last Keep buffer change. Buffer
[-] CLEAR Keep with Work buffer. Buffer
[+] SET Keep with Work buffer. Buffer
[*] ERASE Keep buffer. Buffer
[&] Trap to SID. System
[#] Load TEST pattern. System
[cr] Toggle between MAIN and WORK. Buffer
[0 zero] Perform TRANSFORM. Transform
[1 to 9] Set INCREMENT. Palette
A Show ALTERNATIVE settings. Transform
C COPY settings to ALTERNATE. Transform
D DITHER. Transform
G GRAY. Transform
H HALFTONE. Transform
I INSTALL Dither tables. System
K View KEEP buffer. Buffer
L LOAD a .PI1, .PI3, .DTH file. File
M MAGNIFY. System
N Show NEGATIVE. Palette
Q QUIT. System
R RESET palette to default. Palette
S SAVE a .PI3, .DTH file File
T Change Dither TYPE. Transform
V VERSION. System
X MEZZOTINT. Transform
Z ZERO all other palette values. Palette
WHAT?
LOOKER interactively transforms a low resolution image to a high
resolution image.
BUTS
No GEM, no alerts, no buttons, no menus, no C, no PASCAL, no MODULA2,
not for color systems (not enforced), not a slide show, no mouse, not
a well-behaved application, not a replacement for TINYSTUF or PICSW6
or GRAFCON.
NOT YET
Medium resolution load and transforms, rotate, zoom, mouse draw/erase,
high resolution load as pseudo-low resolution, John Brochu's any-type
file load (thanks, John!), printing, image placement, disk directory,
RLE compression in memory, frame transforms.
________F O R E G R O U N D _______________________________________________
LOOKER can selectively convert each individual color in a low resolution image.
Transforms include a middle gray, a mezzotint, a five-level halftone and eight
preset dithering patterns of 64 gray levels. These dithering patterns may be
interactively changed, saved and loaded. Entire colors may be eliminated or
set to black.
The high resolution output file may be just the default transformation. Or it
can be assembled from one or more images. Mixing of halftoning methods
within a single image is possible and encouraged. Side by side comparisons
of different settings and/or halftone methods are easily accomplished. Colors
in the original may be linked together so that all may be darkened or lightened
equally, thus holding their relations.
________B A C K G R O U N D _________________________________________________
Memory management:
LOOKER maintains two screen buffers, two sub-screen buffers and an input file
block, giving an overhead of 100K. This version can run out of 220K ramdisk
with NO desk accessories on a 520. LOOKER takes all of the memory that TOS
gives it and assumes that the memory between it and the desktop screen is
available. LOOKER doesn't mess with anything below itself, nor does it use
any interrupts.
Inputs in general:
Pressing [Return] or [Enter] will accept the default reply. A 'n/y' stands
for a simple no/yes -- and the default will have the cursor on it. Prompts
for filenames and pathnames are separate. LOOKER doesn't force either case.
LOOKER uses the ST's keyboard buffering and pulls keystrokes off until it
gets caught up. On occasion, LOOKER has crashed when overloading the buffer
(more than 64 characters, I think). Key sequencing is nevertheless useful.
Moving up or down one Palette table entry takes about a second, owing to the
overhead in calculating the micro screen. Shooting past the desired entry is
a common source of irritation. An alternative might calculate and keep all
palette views, but the fourfold increase of input data overrhead would make
a 520's ramdisks tediously small.
________K E Y M A P _______________________________________________________
1 2 Tst 4 5 6 Sid 8 9 xfm - = ` HELP List ( ) Keep
Quit W E Rst Typ Y U Ins Out P [ ] List ^ List Increm. Keep
| | Alt Sav Dit F Gr Hf J Kp Ld view \ Palette Keys Increm. Keep
| | Zro mez C V B Ng Mg , . /| | Increm.
| | spacebar | | xform . view
LOOKER attempts to combine both mnemonic representation -- [H] for halftone --
with a cursor pad 'home' position. What this means is that your left hand
gets to hunt and peck command keys and your right will stay on the cursor
pad. Thus, [cr] -- use your thumb -- flips between the main and work screen
and [0] -- use your little finger -- forces the transform. The KEEP buffer
keys, [/,*,-,+], are modestly inconvenient on purpose.
________F I L E ___________________________________________________________
LOOKER's file handling is simple in extreme. Either command prompts you for
a file name and then tries it. If LOOKER thinks it has an error it will
tell you. LOOKER has no directory command, so write down filenames before
you fire it up. In any case, LOOKER is so small, QUITing to the Desktop is
often the fastest memory aid.
LOOKER uses the filename's extension to find the appropriate routine.
L LOAD filename.PI1 image file to source image buffer.
A low resolution image file stays resident until you load
another or cover it with the test pattern (# command).
filename.PI3 image file to the WORK screen.
A high resolution image file may be loaded directly into the
WORK buffer. It is temporary -- you must either move it to
to the KEEP buffer or take care not to invoke any command that
changes the WORK buffer. Useful to load in area masks that
you have created with DEGAS or whatever.
filename.DTH file to Dither tables.
Loads a previously created custom dither table. Also if you
have tried out INSTALL and hashed up the standard patterns,
you may load LOOKER.DTH to restore them.
S SAVE .PI3 image file from KEEP buffer.
This is a standard high resolution DEGAS file.
.DTH dither table file.
________P A L E T T E _____________________________________________________
After loading a .PI1 file, LOOKER creates a palette table (displayed on the
MAIN screen) by converting each color's red-green-blue settings into a single
number between 0 (white) and 3F (black). This derived value may be freely
changed, so that user may adjust the new monochrome image to the best possible
compromise. All palette commands may be invoked from either the WORK or MAIN
screen, and none change the WORK screen's current display.
[Up] The palette value is SELECTED by moving the cursor up and down
[Down] the Palette table. If the MAIN screen is current, you will see
the cursor move and the MICRO screen change. The dark parts of
the MICRO screen are those parts of the source that contain the
current palette. (A white palette entry will look like a negative
of the image. See [N].)
[Left] The left cursor key will REDUCE the selected palette value.
[Right] The right cursor key will INCREASE the palette value.
[1-9] Number keys will set the adjusting INCREMENT. Additionally,
HALFTONE will set it to 11. Just reset it as needed.
C COPY the WORK buffer's settings to the Alternate settings. This
command also copies the current transformation mode.
N Often colors are really highlights. Sometimes it is useful to
view them as NEGATIVE. This command only changes the MICRO
screen's view of the palette entry, not the transformed result.
Once made NEGATIVE, you may do as you please. When you return to
the palette entry again the display will remember. To remove the
NEGATIVE, press [N] again while the proper entry is current.
O You may OUTLINE the MICRO screen. This is merely a fallout of
internal routines, but what the hell.
R After fiddling with the palette for a while, the source values
can get quite shuffled -- light is dark, dark is plaid, etc.
You may RESET them at any time.
Z To isolate a single palette entry, you may ZERO the rest. The cur-
rent palette entry will remain unchanged. To zero that one as well,
move to another and ZERO again.
A powerful feature of LOOKER lets you change several palette values while
keeping their relations to each other intact. A PALETTE LIST will change
in concert; that is, adjust one by five and all change by five. A list
is signified by a CHECKMARK on the palette table. Unlisted values work
as before and do not alter the list or the list's settings.
Insert ADD the current palette entry to the list. If there is no list,
one will be created.
ClrHome START a palette list. If there is already a list, it is discarded.
Undo DISCARD a palette list. You may change values individually again.
________W O R K B U F F E R & S C R E E N ___________________________
Any valid command may be pressed while the WORK screen is 'current'.
If the command requires additional information the MAIN screen is forced
current. An invalid key also forces the MAIN screen and leaves the keystroke
reminder.
[cr] [cr] is a simple toggle to view the WORK buffer. No changes are
made to the WORK buffer.
A The WORK buffer's settings are saved and the ALTERNATE settings are
used to transform the WORK screen.
D Makes DITHER the current transformation method and the source image
is transformed through a DITHERed halftone, adjusted by the Palette
table settings. The pattern selection is unchanged (see T).
G Makes GRAY the current transformation method. Any palette entry that
is not zero will be forced near middle gray. This transformation is
low contrast; only extremes of light and dark will be discerned.
GRAY is close to the Desktop's gray but has an entirely different
texture. When used in concert with the KEEP buffer, images can be
constructed by adding darks and clearing highlights. This is
LOOKER's slowest transformation.
H A five step HALFTONE is made current and the WORK screen is trans-
formed. This is the fastest transformation. (Side effect: the
palette increment is set to 11. Thus the right/left keys will go
from black to white in five steps.)
T TRADE DITHERing pattern for the next in the series of eight, making
the new pattern current and transforms the WORK screen.
1) rectangular halftone.
2) clustering halftone.
3) vertical.
4) horizontal fine.
5) crosshatching.
6) diagonal.
7) diagonal.
8) "TV" -- horizontal coarse.
X Make MEZZOTINT the current transformation and performs operation on
WORK screen. This method reduces image clarity and is slower than
Dithering. The mnemonic, by the way, is XOR in reference to the
machine language technique used. Sorry.
0 TRANSFORM the WORK screen using the current settings.
________K E E P B U F F E R & S C R E E N ___________________________
LOOKER's output image is built in the KEEP buffer. There is no automatic
creation -- you must choose the pieces and add them. The two commands that
do this, [+] and [-], change the WORK buffer first. If the next command is
STRIKE [/], the KEEP buffer will not be changed. The WORK screen won't be
restored after the STRIKE, facilitating comparisons.
K You can take a look at the KEEP buffer by pressing [K]. If you
haven't kept anything, all you will see is a blank screen. LOOKER
then waits for any keypress and then returns you to the previous
screen. ( MAIN > KEEP > MAIN or WORK > KEEP > WORK) Since LOOKER
doesn't label the WORK and KEEP screens, sometimes you may be con-
fused. Just tap the space bar two or three times, until the MAIN
screen returns.
* ERASEs the KEEP buffer. LOOKER forces the main screen current and
asks you if you're sure. Pressing [cr or Y] will ERASE, anything
else doesn't. [*] isn't much of a mnemonic, but it does line nicely
on the keypad with the next two commands.
/ STRIKE [/] lets you try out an ADD or SUBTRACT without making
a change to the KEEP buffer. [/] must be the very next command
after [+] or [-]. Anything else means that you like the results
and the KEEP buffer will be changed accordingly.
+ The next two build the image. ADD sets on the black pixels in
the image. It copies all of the on pixels in the KEEP buffer to
the WORK buffer. The logical operation is an OR. Thus, if there is
anything in the KEEP buffer [+] will ADD to it.
- [-] performs a logical AND of the WORK buffer, in effect, copying
the white portions of the KEEP buffer. Think of it as SUBTRACTing,
but be mindful that you are just cleaning up the whites. However,
if you SUBTRACT a light image from very dark image, the effect will
approach a straight copy of the light image.
Here's a classic bit manipulation table:
[+] WORK 0 1 [-] WORK 0 1
_________________ _________________
KEEP 0 | 0 1 KEEP 0 | 0 0
1 | 1 1 1 | 0 1
| results | results
The WORK buffer is the one that is really changed at first. If the
next keypress is not [/] then the KEEP buffer is updated. To restore
the WORK buffer, just press [0].
The KEEP buffer, on the other hand, isn't so flexible. If you change
it, it stays changed. Of course, you may ERASE it as often as you
like; but recreating the old version can get problematic. Consider
changes carefully and like an adventure game, when in doubt, SAVE.
________S Y S T E M ________________________________________________________
# Loads a TEST pattern into the input file buffer.
[Help] Shows a command summary on the MAIN screen which is forced current.
I INSTALL or alter the DITHER halftone tables. INSTALL maintains
its own menu of commands, explained below.
Q QUIT is safeguarded: you must reply [y] to exit LOOKER. If you
discover another way out while the Main screen is not current,
you will not see the Desktop. That is, you will have to reboot.
M MAGNIFY shows a 2x view of the Work screen. The cursor pad controls
the image and a ghost box helps orient you. Press any key other
than the cursor controls to escape.
V Prints the current version number of LOOKER, my address for bug
reports and 'donations'.
& If you have a mind to check how LOOKER works, this version includes
a prompted ILLEGAL. Immediately trailing the ILLEGAL is a branch
to the top of the menu. If you have neglected to run LOOKER from
a debugger, a smallish row of bombs will speed you to the desktop.
________I N S T A L L _____________________________________________________
A single source pixel corresponds to four destination pixels. Taken by
themselves, these four can create a five-level halftone. But by applying
the source to a larger pattern more levels can be attained. LOOKER uses
an array of values ranging from 0 to 63. Each value in this Dither table
corresponds to a destination pixel in an 8x8 block of pixels. The blocks are
mapped to the screen as 50 rows of 80 blocks. A 64 level halftone is produced
by assuming a direct relation between a source pixel's palette entry, table
value and location. Different patterns may be introduced to the source image
by variously arranging the values in the Dither (threshold) table. INSTALL
lets you tailor any of LOOKER's eight tables.
The screen shows you the dither table as a grid of numbers, the AUTO-SET
value, and three visual displays -- the complete halftone rainbow and two
single-value squares magnified 2x. These squares show you what the halftone
would look like if all of the source pixels were the same value. You may set
this value as you like, using the V command. The keyboard is remapped, so
the minimal command set is printed as well.
R RETURN to the LOOKER environment.
[cr] Select table to change.
[arrows] SELECT the value to change. The table wraps both vertically
and horizontally.
[##] CHANGE value. For single digit values, you may either use a
leading 0 or any non-numerical key to signify "that's all".
Notice that when the value is accepted, the cursor advances to
the field to the right.
F[##] FILL the dither table with a single value.
V[##] Set the VIEW threshold.
U UPDATE moves the changes to memory.
A 64 level halftone contains the values 0 to 63 with no repeats. Manually
entering the sequence is a hassle, so several commands are provided to
facilitate entry. With exception of the first, all are on the cursor keypad.
A[##] Set AUTO-INCREMENT value. A [cr] starts from zero.
[Help, Undo] Copy the AUTO value to the current cursor position.
[Clr Home] Change the value located by the cursor to the current AUTO
value then INCREMENT the AUTO value.
[Help] Change the value located by the cursor to the current AUTO
value then DECREMENT the AUTO value.
Here's a sample pattern that abandons the halftone concept.
8 32 7 32 6 32 5 32
32 0 32 7 32 0 32 5
0 48 0 0 0 48 0 32
0 63 48 63 48 63 0 6
0 48 0 48 0 48 0 32
0 63 48 0 48 63 0 7
7 0 63 0 63 0 8 32
32 7 0 0 0 5 32 8
Please note: Work out your pattern on paper first. Although INSTALL is
somewhat interactive, it is more suited to rapidly reconfiguring a table that
has already been worked out. In designing it, give thought to the derivative
patterns created by adjacent blocks. Lastly, INSTALL is more or less slapped
together; for its rough spots, I apologize.
_______F O O D f o r T H O U G H T___________________________________
The basis of LOOKER's transformations is the source image's palette. The
monochrome replica of the source image is an interpretation of its hue and
saturation. Photographers are familiar with the distinct differences be-
tween the skills required for color work and those for black and white.
Often an image that 'works' in one form suffers when translated. On the
other hand, many images can be strengthened by judicious emphasizing.
Try XEROXing several photographs. Try to pick a photograph that won't work
and one that will. If you can fiddle with the machine's controls, do so.
Turn off the color on your TV. News shows often look good in either mode.
Color movies and series often lose something.
"There's no substitute for experience":
Buy a roll of black and white film and shoot it up.
Do some fast drawings with one crayon. Then do some with sixteen.
Run LOOKER at every PI1 file you can get your hands on. A monochrome
user's biggest surprise is how mediocre many public domain images really
are -- this emperor often has no clothes.
Your run-of-the-mill color slide has about fifty visible levels of tone. So
does a black and white negative. Modern photographic papers compress this
scale, yeilding ten different tones in a photograph. Photographic negatives
have remarkable resolution. Consider a family reunion and its mandatory
line-em-up-and-smile. Even the cheapest camera results in recognizable
renderings, even when enlarged 20 times or more.
Photographs in the daily paper usually use 85 dots per inch. Each of these
dots vary in size, typically labeled 10%, 20% and so on to 100%. Newsprint
is not the best material on which to print ink, thus only six or seven steps
are actually distinguishable.
However those 85 dots per inch on newsprint can readily exceed the capacity
of the ST's screen. Let's compare 50% grays: 640 pixels in row with half on,
half off equal about 3 3/4 inches of newspaper. The 400 vertical dots are
about 2 1/4 inches. Now vary the newsprint's gray down to 10% and up to 90%.
The printed dot gets smaller or bigger. Not so with the computer screen.
One has to clear more pixels or darken more pixels. So, as we lighten and
darken, the computer screen loses resolution. A guesstimate: a dithered LOOKER
image is comparable to 1" x 3/4" high of newspaper.
Something to try: cut a 1" x 3/4" hole in an index card and hunt through the
newspaper for interesting images.
________M I S C E L L A N Y______________________________________________
Files in this release include: LOOKER.PRG, LOOKER.DOC, LOOKER.DTH.
LOOKER is shareware. What I would like you to do is to put a real dollar bill
in a envelope and mail it to me. Put your return address on the envelope.
I will put the dollar in my wallet and the envelope in a safe place.
Individuals may obtain LOOKER's source code (Alcyon AS68) by sending $10, a
disk and a return mailer. Commercial enterprises are welcome to make me an
offer I can't refuse.
LOOKER is a live program, that is "not done". I will cheerfully correspond
to anyone about LOOKER, its use, its documentation, its future and what a
crummy user interface it has. Write!
Bibliography:
Atari ST Internals by K. Gerits, L. Englisch, R. Bruckmann (Abacus)
Hitchhiker's Guide to BIOS (Atari developer's kit)
Tip: use a black magic marker to block out the cute shit in
the LINE-A 'documentation'.
Computer Graphics by Donald Hearn/ M.Pauline Baker (Prentice Hall)
Programming the 68000 by Steve Williams (Sybex)
Crappy binding, mathematics nonexistent. [Rule of thumb
for judging 68k AL books: multiplication and division
routines for 32 and 64 bit values. Most fail.]
Solid Shape Drawing on the Commodore 64 by Richard Rylander
(Dr. Dobb's Journal, May 1985)
Sets out the underpinnings to dithered halftones and other
marvels. This is a great article.
GRAFCON ST by Patrick Bass (Antic, July 1986)
A Digital Dissolve for Bit-Mapped Graphics Screens by Mike Morton
(Dr. Dobb's Journal, November 1986)
Frederick Hawkins ~ 1020 N. 6th Street ~ Allentown, Penna 18102
July 31, 1987
________G L O S S A R Y__________________________________________________
author One Frederick Hawkins, BFA/MFA in Printmaking from the San
Francisco Art Institute, whose obsession with computers has
prevented him from driving a cab. Still looking for the ideal
hakker's job. Credentials: none. Demerits: likes FORTH,
hates MODULA2, PASCAL, and C; writes only assembly with com-
ments.
buffer A block of memory set aside for a particular purpose. LOOKER
has a WORK buffer, a KEEP buffer, two small window buffers
and an INFILE buffer. Each buffer consists of the image
data and some additional information.
color A set of points in the source image that are all alike.
LOOKER doesn't change the color;; it changes how the color
is represented. This is the absolute bones of an image.
dither A technique whereby a destination pixel is set or not,
depending upon the value assigned to its corresponding source
pixel and a threshold value. In LOOKER, the screen is cut
up into 8 by 8 blocks of 64 pixels, eash assigned a number
from 0 to 63. This number is a threshold and the block is
called the threshold table. If the source pixel's color is
darker than the threshold, the destination pixel is set. By
variously arranging these threshold tables, different halftone
patterns are possible.
DTH The semi-obligatory extension. This is LOOKER's, indicating
the saved dither tables. DTH files are made of 8 tables of
64 bytes. The tables are not demarked in any way except by
length.
halftone A method of simulating a gray by interspersing white and
black dots. Halftones are always patterned.
image A short word for picture.
KEEP The buffer and screen that is used to assemble LOOKER's
output.
list A linked set of colors that may be adjusted in concert.
MAIN The usual desktop screen where text is printed in LOOKER.
mezzotint A random patterning that simulates an etcher's technique.
This is a low resolution transformation because the random-
ness adds noise to the image.
MICRO A quarter-size window used to show the palette and magnified
views.
onebuck A token of your esteem, which, in quantity, may pay for the
disks used in creating LOOKER.
palette In general, a set of sixteen colors that comprise a low
resolution image. In LOOKER, these colors are converted
to a gray level, ranging from 0 to 63 (white to black).
resolution Nominally, this is the sharpness or clarity of an image.
ST usage is based on the number of pixels in a given type of
image. Low resolution is made up of 200 rows of 320 points,
medium resolution has 200 rows of 640 points, and high has
400 rows of 640 points. LOOKER maps a single low rez pixel
onto a 2 by 2 dot of four pixels.
screen The part of a buffer shown to the user and variously changed
by LOOKER's commands.
settings The gray level assigned to a palette color. Sometimes refers
as well to current transform (dithering, mezzotint et al) as
well.
shareware A poor man's justification for spending so much time.
WORK A temporary screen buffer. It must be moved to the KEEP
buffer to be saved.