Mr. Douglas N. Curry Profile

Douglas N. Curry

Principal Engineer at PARC, part of SRI International

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Publications (4)

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Proceedings Article | 1 April 1998 Paper

Color pictorial serpentine halftone for secure embedded data

Douglas Curry

Proceedings Volume 3314, (1998) https://doi.org/10.1117/12.304699

KEYWORDS: Halftones, Printing, Shape analysis, Image quality, Image processing, Glasses, Data corrections, Modulation, Digital watermarking, Electronics

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This paper introduces a new rotatable glyph shape for trusted printing applications that has excellent image rendering, data storage and counterfeit deterrence properties. Referred to as a serpentine because it tiles into a meandering line screen, it can produce high quality images independent of its ability to embed data. The hafltone cell is constructed with hyperbolic curves to enhance its dynamic range, and generates low distortion because of rotational tone invariance with its neighbors. An extension to the process allows the data to be formatted into human readable text patterns, viewable with a magnifying glass, and therefore not requiring input scanning. The resultant embedded halftone patterns can be recognized as simple numbers (0 - 9) or alphanumerics (a - z). The pattern intensity can be offset from the surrounding image field intensity, producing a watermarking effect. We have been able to embed words such as 'original' or license numbers into the background halftone pattern of images which can be readily observed in the original image, and which conveniently disappear upon copying. We have also embedded data blocks with self-clocking codes and error correction data which are machine-readable. Finally, we have successfully printed full color images with both the embedded data and text, simulating a trusted printing application.

Proceedings Article | 4 April 1997 Paper

Analytic clustered halftone dots

Douglas Curry

Proceedings Volume 3018, (1997) https://doi.org/10.1117/12.271619

KEYWORDS: Halftones, Printing, Diamond, Modulators, Binary data, Lithium, Shape analysis, Phase shifts, Densitometry, Image resolution

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An analytic method of constructing high fidelity clustered halftone dots is presented.A phase addressable cell space is created which provides numerically precise 2D edge position information. Exposures are produced with variable intensity modulation to phase shift process direction dot edges, and fine granularity timing is used to adjust fast scan direction edges. This allows symmetrically thresholded halftone dots instead of sequentially thresholded dots. Advantages of this technique are more binary halftone gray levels, reduced labor content, spline based tone correction, device independence, and arbitrary screen angle and frequency. An equation which provides the desired shape and tone response over the intensity range is developed and analyzed. Shape information is extracted which is independent of the target printer characteristics. Highly accurate tone information is obtained by integrating the continuous shape function. A printer-dependent, gray enabled modulator drive function is utilized, and step wedge prints are mae with a nominal tone reproduction curve (TRC). Data from densitometer measurements are converted to spline format, and used to correct the nominal TRC with high relative accuracy. Resulting contourless tone corrected prints show very good linearity and shape definition over the entire intensity range.

Proceedings Article | 18 June 1993 Paper

Hyperacuity laser printer

Douglas Curry

Proceedings Volume 1912, (1993) https://doi.org/10.1117/12.146281

KEYWORDS: Beam splitters, Mirrors, Prisms, Reflection, Polarization, Chemical elements, Imaging systems, Optical components, Beam propagation method, Reflectors

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A hyperacuity laser imager utilizes gray source data and overscanned gray exposure to achieve fully saturated black and white image rendering on the photoreceptor at 4800 addressability in both the fast and the slow scan directions, while maintaining 400 lines per inch frequency response. Conventional laser printing techniques render bitmapped images at resolutions finer than required by the human visual system (for example, 600 to 1200 bits per inch) in an unsuccessful attempt to meet a related requirement for edge placement precision of text, line art, and halftones. This excessive bitmapped resolution is inefficient and cumbersome to maintain in a printing system and is still not nearly enough to satisfy the human visual system's need for edge precision. On the other hand, a hyperacuity imager has the edge precision necessary to satisfy the human visual system's needs, and trades off excessive resolution to do so. This paper examines the overscanned, gray exposure characteristics of the hyperacuity laser imager and how it can be viewed as a natural evolution of the current trends in laser printing technology. In addition, it establishes an order of magnitude relationship between addressability and frequency response for a hyperacuity imager, which is shown to significantly match the needs of the human visual system.

SPIE Journal Paper | 1 April 1993

Hyperacuity laser imager

Douglas Curry

JEI, Vol. 2, Issue 02, (April 1993) https://doi.org/10.1117/12.10.1117/12.143462

KEYWORDS: Imaging systems, Printing, Image resolution, Composites, Visual system, Boundary scan, Nonimpact printing, Phase shifts, Human vision and color perception, Image enhancement

Read Abstract +

A hyperacuity laser imager utilizes gray source data and overscanned (enhanced sampling reconstruction) gray exposure to achieve fully saturated black-and-white image rendering on the photoreceptor at 4800/in. addressability in both the fast and the slow scan directions, while maintaining a 400 lines/in. frequency response. Conventional laser printing techniques render bit-mapped images at resolutions finer than required by the human visual system (for example, 600 to 1200 bit/in.) in an attempt to meet a related requirement for edge placement, precision of text, line art, and halftones. Unfortunately, this excessive bit-mapped resolution is inefficient and cumbersome to maintain in a printing system and is stiil not nearly enough to satisfy the human visual system's need for edge precision. On the other hand, a hyperacuity imager has the edge precision necessary to satisfy the human visual system's needs, and trades off excessive resolution to do so. We examine the overscanned, gray exposure characteristics of the hyperacuity laser imager and discuss how it can be viewed as a natural evolution of the current trends in laser printing technology. In addition, an order of magnitude relationship is established between addressabiity and frequency response for a hyperacuity imager, which is shown to significantly match the needs of the human visual system.

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