Easel: a system for artists. (evaluation) Barbara Mackowiak.

If you sit down at a computer paint system, you expect to be able to do some of the basic things you do with pen and brush, ruler and compass. Draw a straight line or a circle. Erase it and redraw it in a wider line. Paint in some red here, some blue there. Soften the edge with a little airbrushing.

Then you push forward a bit. Say you would rather all that red were a little brighter. Perhaps move that bit of freehand drawing in the corner more toward the center, and make it twice as big. Then you might like to see how the picture would look if the right side of the screen were a mirror image of the left side. Soon you are altering resolution, remapping colors, and storing in buffers, as no human with ruler and compass ever could.

This is a fairly accurate description of the path I followed with Easel, a professional graphics arts program developed by Tim Arts Inc. The name is an acronym for Editor and Animation System with Extensible Library.

Using Easel, you draw with an electronic pen and tablet, with gestures similar to those used for drawing on paper. The image appears on a high quality RGB monitor.

As soon as Easel is loaded into the computer, the pen is active. Any freehand drawing you do with the pen appears immediately on the monitor screen.

To choose a different pen type, to change a color, to retrieve an image saved on the computer disk, or to select a command for changing an image onscreen, glide the digitizing pen down on the tablet. This brings to the bottom of the screen a menu containing commands, a color palette, and a status box with information on the current drawing mode. To select a command, put the cursor in the menu command box and press down on the pen.

If you want information about any menu command, press the "doc" icon before selecting the command. A concise description of the command will appear on the computer terminal.

The Main Menu comes up on the screen whenever Easel is loaded. It lists other menus in the program, each of which carries a set of related commands.

The Pens Menu has the basic drawing modes, such as Pen, Brush, Airbrush, and Line, which can appear in any of eight sizes. The Brush Menu has several special brushes, as well as a command which allows you to create your own brush. Color has commands for changing a single color; CMaps (color maps) for changing several colors at a time; Fills for changing a color or a selected area of the screen; Shape for drawing simple geometric figures; Move for manipulating images onscreen; Frame for saving images on disk and recalling all or part of an image back to the screen.

The final entry in Main is the Etc Menu. Like Main, Etc is a menu of menus. This layering opens up the system, allowing Easel to be extended indefinitely. In the Easel I used, the Etc Menu lists Miscs, a menu of commands, such as grids and gravity lines, that help in arranging images; SetRes, a menu of commands for moving between high- and low-resolution screens; Scale for rescaling, tapering, and putting images into perspective; Shear for shearing, tilting, and rotating images; Video for digitizing an image with a video camera; and Cells for storing and accessing image cells for custom brushes and fonts.

The pictures accompanying this article illustrate some of the effects possible with Easel. The text below describes the commands I used in making the images. A Simple Landscape

The sky in Figure 1 is composed of colors shaded from pink to blue through the Tint command. In preparation for tinting, I changed two colors--the pink at the horizon and the darkest blue at the top of the picture. To produce the pink, I used the RGB (red/blue/green) command to make the color in position one of the palette a medium red; then, using the Mix command, I added white and blue to make the appropriate shade of pink. For the darkest blue, I used RGB on the color in position seven making it a medium blue, then used Mix to darken it.

The Tint command allows you to tint a range of colors from the first color chosen to the second color chosen. By pressing the pink and then the blue, I tinted the five intervening colors of the palette.

As it happens, I made these color changes first, then began drawing. However, I could just as well have done the picture first, composing the sky of any consecutive colors in the palette, and then tinted the colors. Any changes in color mapping in the palette appear thoughout the image onscreen. Variations on a Theme

The system I used in Figures 2a, 2b, and 2c determines colors through mapping. In color mapping, the value of a pixel is not a specified color; instead, it is an index to a map or table of color combinations and variations of the basic red, blue, and green that make up all video colors. The table entry determines the hue and intensity of the color on the graphics screen. "Mapping" a color means referring to a place on this table for the composition of the color. With this system, even though only 16 colors can appear on the screen at a time, the number of colors possible is vastly larger.

There are two menus of commands that control color mapping. Commands in the Color Menu affect one selected color, which appears as the "current color" in the status box of the menu. Mix, used in the previous picture, lets you blend any other color into the current color by putting the cursor over the color to be blended in; the chosen color will continue to be added in as long as you press on the pen. Luminance lets you adjust the brightness of a color by moving the digitizing pen left or right on the tablet. RGB lets you selectively change the red, blue, or green component of a color. Xchcol exchanges any two colors onscreen.

Commands in the CMaps Menu affect the mapping of several colors at a time. Tint, used in the previous picture, shades all colors from the first color pressed to the second color pressed. RMap brings to the screen a palette of random colors that change continuously as lon as you keep the cursor in the RMap command box.

Since a change in the mapping of any color changes all instances of that color onscreen, you can quickly see the effect of any change on the entire image. This series shows the same image with different color mappings. (I have left the menu onscreen to show how the palette looks for each picture.) A Strange Prism

Easel contains a variety of pens and brushes. These include special brushes, such as Airbrush, which deposits a spray of up to four colors, and Char, which deposits characters in a brush mode, as well as the standard brushes that lay down solid color. In general, pens and brushes replace whatever color they cover. That is, a red line will be red, whether it covers black, green, or yellow.

The X brushes, however, activate a Boolean "exclusive OR" function.

Used over background (position 0 in the palette), each color paints as it appears in the palette. Used over another color, the X brush produces a third color. For example, the color in palette position 10 1010 used over the color in position 9 1001 produces the color in position 3 0011 What color actually appears depends on how the color in the position is mapped.

In the Prism shown in Figure 3, I did the basic figure with the standard Brush and softened the borders between colors with an Airbrush spray, using equal parts of each color. The diagonal bands I did with Ring X, a ring-shaped brush that uses the exclusive-OR function. The colors of both the basic figure and the diagonal bands are sequential colors from the default palette--the palette that comes up whenever Easel is loaded. Concrete Poem The Type command allows you to type on the graphics screen from the keyboard. The position of the cursor when you enter the type mode determines whether the text begins and sets the left margin. Keys such as DELETE, RETURN, space bar, and SHIFT work as usual. Typed text appears in the current color and covers any color onscreen. Once you leave the type mode (by pressing the ESCAPE key), the type onscreen is just like any other part of the image, and you can manipulate it with any of the graphics commands.

For the picture in Figure 4, I typed each of the four basic words onto the screen, positioned them with the Move command and changed their dimensions with the Zoom command. I doubled the size of land and expanded the height of sky. Sunset remains in its original size.

Rather than typing each word over and over, I used the Dup command, which allows you to duplicate an image repeatedly to fill a defined area of the screen. For the clouds, I typed cloud and then made a "stamp" of the word with the Rubberstamp command. The entire word would then appear whenever I pressed on the pen.

After all the words were in position, I used Maskbrush to recolor some of them. Maskbrush lets you paint over a selected color and masks out all the others, so I could easily recolor some of the yellow sunset words to red without harming the surrounding background color.

Although Easel is available to run on a variety of hardware, I usd a Z80-based system with an image resolution of 756 x 482. Sixteen colors were simultaneously available out of a possible 4096. I photographed the pictures directly from the monitor.

Easel is supported by Z80, 8086/88 and 6800 systems including the IBM PC and is customized to work on a variety of frame buffers. The prices, as well as the implementation of some features of the software, vary with the hardware but begin at $625.

Time Arts Inc., 4425 Cavedale Rd., Glen Ellen, CA 95442.

Products: Time Arts Easel (computer program)