Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1998-12-22
2001-09-04
Rogers, Scott (Department: 2624)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S001700, C358S300000
Reexamination Certificate
active
06285463
ABSTRACT:
BACKGROUND OF THE INVENTION AND MATERIAL DISCLOSURE STATEMENT
The present invention relates to a color imaging system wherein the average of one or more colors is used to modify the saturation of another color.
Blooming is a problem resulting from constraints in intensity and misalignment tolerances as found in many imaging scenarios and types. Much of the art solving blooming problems is directed primarily toward video and CCD type cameras. However, color imaging systems such as video display monitors and print systems can also exhibit blooming problems in their output. By “blooming” we are referring to shapes in an image which exceed their intended edges or boundaries and are thus larger than desired in a manner objectionable to the human eye. Examples of blooming include, line growth and narrow white space fill in. Two important parameters affecting blooming in color systems are alignment, and saturation or intensity. The consequences of these two parameters are manifest in both color image display and color image print systems. The method and apparatus disclosed here are applicable in both such systems as is apparent to one skilled in the art. However, for purposes of discussion the focus will be upon printing systems. In particular, the discussion will focus on xerographic, electrophotographic or any other electrostatographic printing processes.
In a typical electrostatographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize its surface. The charged portion of the photoconductive member is exposed by a writer, for example: by light from the image of the original document, or by a raster output scanner (ROS) in the case of an electronically stored image. Exposure of the charged photoconductive member selectively dissipates charge in the irradiated areas. This renders a record, with the electrostatic latent image on the photoconductive member corresponding to the informational areas contained in the original document. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing developer material into contact with the surface of the photoconductive member. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image by electrostatic force thus forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet.
The foregoing generally describes a typical black and white electrostatographic printing machine. With the advent of multicolor electrophotography, it is desirable to use an architecture which comprises a plurality of image forming stations. One example of the plural image forming station architecture utilizes an image-on-image (IOI) system in which the photoreceptive member is recharged, reimaged and developed for each color separation, followed by a single transfer of all colors to paper. This greatly simplifies the transfer system, hence the system architecture, in comparison with a traditional system where each color is transferred to paper separately. As such, IOI machines can be single pass or multipass. In single pass IOI machines the charging, imaging, developing and recharging, reimaging and developing, etc followed by transfer to paper, are done in a single revolution of the photoreceptor. This requires multiple charging and imaging stations. In multipass IOI architectures, each color separation is formed with a single charging and imaging station but with different development stations, though still with a single transfer operation of all the colors. The single pass architecture offers a potential for much higher throughput.
In an IOI machine the second, third and fourth exposure or imaging stations need to image through prior developed toner layers, hence their intensities need to be increased. With IOI all the desired toner colors are built up on the photoreceptor before transferring to a page and fusing. The first color toner is applied in the same manner as black and white or single color electrophotography. Everywhere, the first color is applied directly to the photoreceptor. Thereafter one or more subsequent colors are applied over the first color. Where a color blend is desired, the second color toner is applied superimposed over the first color toner. Where only the second color is desired however, it is applied directly upon the photoreceptor. The result is that a subsequent color toner layer develops, in some places over the prior toner layer, and in other places directly upon the photoreceptor. This requirement creates a problem in the exposure step prior to this second toner development step. For that exposure step, the raster output scanning (ROS) level if set to the same exposure level as before, will not achieve the same photoreceptor charging levels because the laser needs to image through the first toner layer. This ultimately results in an insufficient mass of toner with attending color and saturation problems in the print. Thus there is a need to increase the ROS exposure level. However, such an increase, when applied to areas where there is no prior developed toner on the photoreceptor, means the exposure level is now too high, and this causes a “blooming” problem (i.e., line growth and narrow white space fill in).
By way of illustration, consider an IOI machine where the colors are developed in the order of yellow, magenta, and cyan. Current practice in IOI xerography calls for high ROS exposures for the cyan separation to discharge the photoreceptor to an equal voltage under magenta and yellow toner and bare photoreceptor. If two exposure powers are available, one for bare photoreceptor and one for areas with previously developed toner, one is freed from the constraint of over exposure because the bare photoreceptor exposure can be independently controlled so as to be equal to the exposure found under toner layers. This is disclosed with U.S. patent application Ser. No. 08/786,611 assigned to the present assignee and incorporated by reference herein, which teaches that such an approach is electrostatographically feasible and shows the image quality benefits which result. In that particular implementation of a multiple exposure technique, transfer of information from the previous channels to control the exposure levels when printing the next separation are utilized on a pixel by pixel basis. However, such an approach relies on near perfect alignment at each station as the photoreceptor is exposed for each color. Where misalignment exceeds one pixel width in amount, which is typical, blooming effects again become manifest. Blooming as resulting from constraints in intensity and misalignment tolerances is a problem found in many imaging scenarios and types.
U.S. Pat. Nos. 5,450,211 and 5,561,743, address as a cause of blooming the change with temperature of focal distance and attendant change of magnification (change in beam diameter). Disclosed is a copying machine for forming an image by a scanning laser beam which is emitted from an optical system on a photosensitive member. Photosensors are provided at optically equivalent positions to a beginning portion and an end portion of a scanning line on a photosensitive member. A scanning time of a laser beam in the main scanning direction is measured by these photosensors. The measured time and a standard time for a copy magnification set by an operator are compared, and a correction value is calculated, and at the same time, magnification in the main scanning direction is corrected using the correcting value. Also, focusing (adjusting of the beam diameter) is carried out using the photosensors. Each of the photosensors contains a photoelectric transfer element, and a beam which comes through a slit is incident to the element. Each photosensor is provided with two slits. One i
Lin Ying-wei
Loj Katherine
Rogers Scott
Wait Christopher D.
Xerox Corporation
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