FROM IMAGE TO WOVEN STRUCTURE: A VIDEO-COMPUTER SYSTEM FOR TEXTILE DESIGNERS

Lisa Lee Peterson

Introduction

The work that led to this paper began as the result of two misconceptions.

Ten years ago I saw some woven portraits which were made in China (Fig. 1). I imagined then that a computer had translated photographic images into electronic impulses and powered a loom to weave the portraits.

A few years later, while working to improve computer systems used in the Jacquard textile industry, I suggested that video should be used to input design information. Why not speak to the computer in a language that it understands? Since computer monitors and television sets look alike, I incorrectly assumed that computers and videos operated on similar systems.

Televisions operate on an analog system. Computers are digital. China's supercomputer is hundreds of skilled textile technicians working thousands of hours translating continuous-tone photographs into hand-painted dots of weave patterns.

The process of converting a design or image into Jacquard-woven fabric is time, labor, and skill-intensive if done by hand. Textile computer systems can speed up the process but, as yet, have not been able to match the standards of skilled technicians.

Macintosh computer

Since leaving the industry in 1982,1 have been exploring methods of translating images into Jacquard-woven structures using video and computer tools. New devices such as the Macintosh computer and inexpensive video digitizers enable me, as an individual, to pursue solutions for industrial problems.

I have been looking for a way to integrate woven structure with any image quickly and easily. The video camera captures an image as an

ARS TEXTRINA 7 (1987), pp. 109-160

analog signal and the digitizer translates this format into digital data readable by the computer.

The system allows me to manipulate this digitized picture in any number of ways. I have chosen, in particular, to translate the image to woven structure.

The Macintosh screen is analogous to a point paper (the graphic representation of a weave structure for Jacquard). Each screen point on the Macintosh computer monitor, unlike on a conventional television screen, has only two states: ON or OFF. If the point is ON, it appears as black on the computer screen; if the point is OFF, it is white.

In a weave graph, each square represents one intersection of a warp thread and a weft thread. If the warp thread is on top of the weft thread, then the corresponding square on the weave graph is black. If the warp thread is below the weft thread, then the graph square is white.

MAGIC video digitizer

From the various video digitizing systems available, I selected MAGIC (the acronym for MAcintosh Graphics Input Controller), developed by New Image Technology.

This video digitizer converts continuous-tone images (coming in through the camera eye) into numerical values on a scale of 0 to 255. 0 represents the darkest value, or black; 255 is the lightest value, or white. Intermediate values of 1-254 are varying levels of grey (Fig.2).

MAGIC makes three types of pictures based on the data provided by the digitizer: high-contrast black and white (Fig. 3); outline (Fig. 4); and pattern (Fig. 5). All three have possible applications for textile design. I have done most of my work with pattern pictures because they resemble Jacquard point papers.!

The program user can assign specific patterns to the different ranges of light intensities (Fig 6). MAGIC provides a selection of ready-made patterns. Unlike most other digitizers for the Macintosh, MAGIC allows the user to design his or her own patterns.

1 For the purposes of this paper, the word "image" will refer to the original source material, whether it is a real event, slide, photograph, or drawing. "Picture" will refer to the pattern picture that is the result of the computer-digitized image.

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Each pattern is based on a matrix or grid of 8 squares by 8 squares. Each square can be either black or white. The darkest possibility is all 64 squares black. Conversely the lightest pattern is all 64 squares white. Any pattern in between would appear as some value of grey (Fig. 2).

There is a correlation between the pattern matrix and a weave draft. In most instances, a weaver would not draft all 64 squares as all black or all white. However, it is possible to develop a range of grey values, based on weave structures, between the two extremes.

Imaging

Some of the pattern matrices I designed are:

1. double-ended 4-shaft twill (Fig. 7)

2. single-ended 4-shaft twill (Fig. 8)

3. double-ended 4-shaft herringbone twill (Fig. 9)

4. single-ended 4-shaft herringbone twill (Fig. 10)

5. single-ended 8-shaft twill (Fig. 11)

6. single-ended 8-shaft satin (Fig. 12).

The 8-shaft weaves, with seven different configurations, offer the widest range of woven grey values possible within the 8 by 8 pattern matrix.

In order to integrate an 8-shaft weave pattern with the computer's patterning function, I divide the light intensity scale of 0 to 255 into seven segments. I then insert one of of the seven weave configurations into each of the segments. The pattern representing the darkest value is a 7/1 warp-faced weave, the lightest value a 1/7 weft-faced weave. The greater the number of weave configurations in a grey scale, the more detailed the picture (Fig. 13).

The pictures of my son, Toby, were digitized from a 35mm slide (Fig.14). The 4-shaft twill pictures (Figs. 15 and 16), with only three weave configurations, are coarse in comparison to the seven- configuration 8-shaft twill or satin (Figs. 17 and 18). The six- configuration herringbone twills are an extension of the 4-shaft twills. Adding the extra twill direction does not increase the grey value levels, but results in an image with more pattern differentiation (Figs. 19 and 20).

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Resolution

Because the images are coarsely resolved, a viewer can best recognize the pictures of Toby from a distance.

In order to improve resolution, I needed to start with a larger image than the slide of Toby.

To simulate finer resolution, I focused on a smaller portion of another image. The same number of pixels that might be used to articulate a whole image could then articulate a portion of that same whole, in greater detail (Fig. 21).

Using the 8-shaft satin pattern, I digitized a drawing by Raphael. This drawing is 10 times larger than the slide of Toby (Fig. 22), and the computerized picture is much better articulated (Fig. 23). However, an enlargement of the right eye, which is 80 pixels wide, shows that the details are not well defined (Fig. 24).

With a close-up lens, I digitized the same eye so that it measures about 150-160 pixels wide (Fig. 25). This is equivalent to the number of warp ends in Chairman Mao's eye in the Chinese-woven portrait (Fig.26).

The Macintosh computer screen is 512 pixels (screen dots) in width by 342 lines per inch. In weaving terminology, this is analogous to 512 ends by 342 picks.

In the example of the Chairman Mao portrait, the fabric is woven at 68 ends per inch. If the pick count of the fabric were also 68, the maximum portion of the portrait that could be represented on the Macintosh screen would be 7.5 inches (512 ends/68 epi) by 5 inches (342 picks/68 ppi).

The finished size of the Mao portrait is 18.5 inches wide by 28 inches high. In order to capture the entire image at 68 ends and picks per inch, I would have to digitize the portrait in 18 separate segments (Fig.27).

A complicating factor in all of these calculations is that the pick count is actually 88 picks per inch. In order to represent precisely the Mao portrait on the computer monitor, a rectangular-shaped pixel or, more likely, a much higher resolution monitor is needed.

Computer monitors exist today with widths in pixels of 1024, 2048, and even 4096. A monitor of any of these resolutions would reduce or

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eliminate the present need for use of close-up lenses, fractured images, and other make-shift methods of resolution improvement.

Imaging with 2-simultaneous weft structures

Another set of patterns that I designed are based on double cloth weaves:

1. 4-shaft plain weave double cloth: odd ends only, even ends only, and a composite of both odd and even ends (Fig. 28);

2. 8-shaft twill double cloth: odd ends only, even ends only, and a composite of both odd and even ends (Fig. 29).

In the textile industry, point paper technicians use several colors instead of only black and white to graph multiple-layer weaves such as double cloth.

At the firm where I worked, the common Jacquard fabric is a 3- simultaneous weft, end-and-end warp, multi-layer construction (Figs. 30 and 31). In a typical 64 end by 72 pick segment from the point paper, six colors are used: one for each of the three weft colors; black for the dark warp end; white for the light warp end; and blue to flag out-of-sequence binders.

The color enables the technician to see the design very clearly and any anomalies can be easily spotted. In a black and white version of the same 64 end by 72 pick section, the design is difficult to decipher (Fig.32).

The Macintosh, however, is black and white only. In order to reproduce a color rendition of a point paper for double cloth, I separated the layers.

Using a photograph of my husband, Skif, and Toby (Fig. 33), I made two pattern pictures. One weave configuration for odd-numbered ends was used to make the first picture. The complementary configuration for even-numbered ends was used for the second picture.

The pattern pictures that resulted were positive and negative pairs (Figs. 34 and 35; 36 and 37). Combining the positive and negative pictures, using two different colors, would result in a color weave diagram. Use of additional colors would clarify weave structure even further.

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If I had the possibility of color, the pattern matrix would be painted in four colors: 2 weft colors; plus black and white for the odd and even warp end stitchers.

While the same information is in the black-and-white both-layers- together versions (Figs. 38 and 39), the picture and weave construction would be more easily deciphered in color. The Imagewriter II could be used with any of a number of color printing programs to print a color weave diagram.

Other types of images

Digitizing portraits enabled me to see whether or not I was getting a recognizable image. I then used the same procedure to digitize textural types of images.

A satellite photo of the Sand Hills of Nebraska (Fig. 40) was digitized in an 8-shaft satin (Fig. 41) and a 4-shaft herringbone (Fig. 42). The pictures, still recognizable as sand, would make beautiful all-over textures as woven fabric.

In another experiment, I made a black and white high-contrast picture of an infrared satellite photo of the cornbelt region of Iowa and Minnesota (Figs. 43 and 44). I then converted the black and white picture into a pattern picture, using only two weaves, a 2/6 twill right for black and a 2/6 twill left for white.

A lattice or maze-like pattern resulted (Fig. 45), which I am now putting into a half-drop repeat for a screen print design. A woven version would be a crepe type of fabric.

Discussion of advantages, applications, and refinements needed for the video digitizer system

Advantages

Textile computer systems that are in used industry today optically or manually scan and digitize specially prepared designs (Fig. 46). A video digitizer analyzes and reproduces real events (people, landscapes, skies, foliage, or photographs of the same) with relative speed and ease. These factors, along with video's portability, create possibilities for a wider range of source material for textile design.

Textile scanners digitize a design, line by line, taking minutes or hours, and then compile the digital data with weave structures. Video systems capture the image and integrate it with weave structure in a

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matter of seconds, thus allowing the user to view the picture while making instantaneous adjustments (Fig. 13).

Once the picture is completed, printouts can be checked for any corrections that need to be made. Paint programs allow pixel by pixel corrections to be made and facilitate repeat design.

Applications

The computer-digitized video pattern picture has all the data necessary to drive a Jacquard card cutter directly. Since interfaces exist for computer scanning systems and card cutters, I assume that an interface for a computer-video system is all but accomplished.

Current output is in the form of laser and screen prints. The double- cloth positive and negative images have a direct application as color separations for screen printing. This idea could be further extended to obtain three or more separations based on color differences and/or light intensity levels.

Refinements

1. Using the built-in electronic color filtration system of a sophisti - cated color video camera, video could be used to make color separations for screen prints. A color monitor and color printer would greatly assist in the analysis of multi-layer fabric constructions.

2. The pattern matrix in the MAGIC system is 8 by 8. This is ex­ tremely limiting in terms of weave constructions. The weaves used in the Chairman Mao portrait are based on a 32 by 64 matrix (a single warp, 2-simultaneous weft construction). The weaves in the industrial example are based on a 24 by 48 matrix (a 2 warp, 3-simultaneous weft construction) (Fig. 47).

A modification of this system allowing the user to define any size matrix, would increase the number of weave configurations that could be used to make pattern pictures. It would also increase the number of grey levels that could be obtained.

3. The grid ratio on the Macintosh is one to one. In weaving, the ratio of warp ends per inch to weft picks per inch is rarely 1:1 (perfect tabby). If the grid ratio, or perhaps the shape of the pixel itself,could be modified, the pattern pictures could be made to match the actual ratio of the woven fabric (Fig. 48).

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At present, if the actual end or pick ratio varied from 1:1, the woven picture will either be squashed or elongated. The best solution to this problem is probably the use of a computer system with a screen resolution of 2048 by 2048 or greater.

4. A close-up lens yields greater resolution, but also decreases the area of the image that is digitized. This results in many small segments which must be pieced together to recreate the whole picture (Fig. 27).

A possible solution would be, as above, to increase resolution of the computer screen. Another possible, but less accurate solution might be to adapt a step-and-repeat machine to move the video camera in precise increments over the entire image.

5. Once the entire image was compiled, all corrections made, the cards cut (assuming an interface existed), the fabric could be woven on a Jacquard loom. Ultimately, I imagine the cards will be replaced by a computer-programmed cartridge which will operate the Jacquard to create a woven picture.

Then the supercomputer that I imagined China had would be a reality (Fig.49).

Photo credit for all slides - SkifPeterson

Department of Creative Arts Purdue University West Lafayette, Indiana U.S.A. 47907

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Figure 1. Portrait of Chairman Mao, woven in China, c. 1975

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