Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
1999-03-05
2001-09-18
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C250S559160, C250S559400, C356S446000
Reexamination Certificate
active
06291829
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to devices and methods for identifying media and more specifically to devices and methods for identifying recording media in a printer or reproduction device.
BACKGROUND ART
Modern printing devices, for example, ink jet and laser printers, print on a wide range of print media. Such media include plain paper, glossy or coated papers, and plastic films including overhead transparency film. For optimal print quality, operating parameters of these printers may be adjusted to meet the requirements of each print medium. Parameters in the image rendering process, in a host computer or in an “on-board” computing engine in the printer, also depend upon media type. For example, the “gamma” (i.e., tone reproduction curve) used for reflective prints (on paper and other reflective media) is different than that used for transparency media. This is required to adapt the printed image to the characteristics of the human visual response under different lighting and viewing conditions. Therefore, both the recording process in the printer and the image rendering process, in a host computer or on-board computing engine, may require knowledge of media type for optimal print quality.
The software controlling the rendering process and the printer, including the printer driver, sometimes gives the user the opportunity to specify the recording medium. Parameters of the rendering and recording processes are then adjusted according to the recording medium and the quality mode selection. However, users may not always make the correct choice. In addition, specifying the choice is often inconvenient when multiple copies on different media are desired as occurs when overhead transparencies and hardcopy for handouts must be produced from the same data file.
One approach to this problem is to use recording media marked by machine-readable, visible, near-visible, or invisible marks forming bar codes or other indicia that specify media type and automatically provide process information to the printer. While this offers a practical solution, not all media available to the user will contain these codes.
Other approaches known in the art distinguish between two broad classes of media, transparency film and paper. For example, U.S. Pat. No. 5,139,339, to Courtney et al. discloses a sensor which measures diffuse and specular reflectivity of print media to discriminate between paper and transparency film and to determine the presence of the print medium. Other art cited in Courtney et al. deals mainly with analyzing specular reflections over an area. U.S. Pat. No. 5,323,176 to Suguira et al. describes a printer with means to discriminate between “ordinary printing paper” and “overhead projection transparency film” on the basis of its transparency or opacity. However, these references, which rely on gross properties of the print medium either in reflection or transmission, do not allow any finer distinctions. What is needed is a method to distinguish print media that goes beyond the simple categorizations of the prior art.
SUMMARY
The present invention relates to a method and device for identifying recording media in a printer. The invention utilizes surface properties and fine structure of the media revealed by illumination from one or more directions to distinguish among different kinds of plain papers, coated papers, photographic papers, and transparency films.
When the medium is bond paper, a surface-texture image is obtained by directing illumination at a grazing angle relative to the surface. Grazing angles is below about thirty degrees, and preferably less than about sixteen degrees are used. By directing light at such angles, surface depressions and raised surface irregularities cause shadows, creating an imagable surface texture or pattern rich in detail. For typical bond papers, fibers in the paper surface create structural features with characteristic dimensions in the range of 1 to 100 &mgr;m. Viewed with resolution-limiting optics, only the larger shadow features are seen and produce an image unique to bond paper. Thus, a preferred combination for bond paper is grazing illumination and low resolution optics which highlight the lower spatial frequency features.
For highly glossy surfaces, such as photographic paper, specularly reflected light from normal illumination provides an especially rich image of closely spaced features with characteristic feature dimensions on the order of 5 &mgr;m. Thus a preferred combination for photographic paper is normal incidence illumination with high magnification.
Coated media and the surfaces of transparencies are relatively smooth and flat but have some relatively sparse distributions of small and shallow holes that can be imaged with some contrast using grazing illumination and a modest magnification.
According to an aspect of the present invention, a suitable compromise enables a device for identifying recording media to use a single choice of optics in combination with both normal and grazing incidence illumination to image distinguishing features of bond paper, coated paper, photographic paper, and transparencies.
The device of one embodiment of the present invention includes one or more sources of illumination, positioned to irradiate the recording medium surface at a grazing incidence, or at normal incidence, or positioned to direct light through the recording medium. These sources produce an optical signal representative of the recording medium. The optical signal is effectively captured by imaging optics and detected by an optoelectronic sensor with a projected pixel dimension on the surface of the recording media less than 100 &mgr;m. The optoelectronic sensor typically is a two-dimensional photodetector array. Alternatively, a linear array could be used or the recording medium could be scanned past a linear photodetector array to produce a two-dimensional image.
The photodetector array is typically connected to at least one analog to digital converter (“ADC”) through analog buffering and switching circuits. These circuits present the analog voltages (or charges) from each photodetector in the array serially to the ADC, or present values row-wise or column-wise in an arrangement where there are parallel ADCs. Digitized values, representing the light received from the media by each element of the photodetector array, are communicated to a processor to perform the required calculations to identify the media. A set of characteristic values is extracted representative of the media and is communicated, for example, to the host computer to provide information to the printer driver.
Optimal settings for parameters in the rendering and recording process are associated with each type of recording medium. Frequently, the printer driver on the host computer controls the parameters of the rendering and recording processes. For rendering, these include selection of tone reproduction curves, halftone and error-diffusion algorithms, color maps and gamut adjustment and others. For the recording process in an ink jet printer, these include ink drop volume, number of ink drops per pixel, number of passes of the printhead over a pixel, the order and pattern in which drops are printed in a pixel or a region of pixels, and information presented on the printer's display panel.
The determination of media type is often preferably made in the host computer for two reasons. First, the media type determines parameters for both image rendering and printer marking processes. Images are rendered with consideration to parameters of the marking process, and rendering and marking must be coordinated. Second, because new media may be introduced and process changes may require tuning the identification process, the manufacturer can update the capability of the host/printer system to differentiate media by providing the user with an updated printer driver containing the identification criteria and categories. It is possible, however, with future proliferation of information appliances, that the determination of media type may be done w
Allen Ross R.
Tullis Barclay J.
Hewlett--Packard Company
Lee John R.
LandOfFree
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