Uniform exposure of photosensitive medium by square intensity profiles for printing

• US 6,011,631 A
• Filed: 01/29/1997
• Issued: 01/04/2000
• Est. Priority Date: 01/31/1996
• Status: Expired due to Term

• Current Assignee: Punch Graphix International NV (ColourOz TopCo), Texas Instruments, Inc.
• Original Assignee: Agfa-Gevaert N.V., Texas Instruments, Inc.
• Inventors: Broddin, Dirk K., Janssens, Robert F., Nelson, William E., Deschuytere, Frank A., Venkateswar, Vadlamannati
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): TOATLEY, GREGORY J
• Application Number:
  US08/791,061
• Time in Patent Office: 1,070 Days
• Field of Search: 359/223, 359/224, 359/230, 359/846, 348/771, 347/239, 347/241, 347/242, 347/243, 347/244, 347/255, 347/256-260, 358/298
• US Class Current: 347/239
• CPC Class Codes: G03G 15/5037 the characteristics being an electrical parameter, e.g. voltage
• CPC Class Codes: G03G 2215/00042 Optical detection
• CPC Class Codes: H04N 1/407 Control or modification of tonal gradation or of extreme levels, e.g. background level

Abstract

In classic optical rendering systems, the spot, illuminating a microdot on the photosensitive medium, is designed to overlap with neighboring microdots, typically having an overlap of 1.7 times the pitch of the microdots, for a luminous intensity of 1/e² the highest intensity. A "sharp" photosensitive medium, such as a photographic film used in graphical applications, generates a binary circle, obtainable by thresholding. The area of such a circle is too large, which results in higher dot gain.

Many systems, such as electrographic systems, do not behave as a "sharp" medium. If intermediate energy levels are used, in order to obtain continuous tone or multiple density levels, thresholding behavior may be avoided by appropriate choice of energy levels. Such a different sensitometry results in specific requirements for the energy distribution for each microdot.

A square shaped uniform energy distribution within the space allotted to each microdot, allows for multiple density levels, without severe sensitometric requirements.

Claims

1. A method for generating an image on an image carrier comprising the steps of:

partitioning said image carrier in a plurality of microdots, which fill said image carrier completely and do not overlap one another; and

applying to each microdot an energy distribution which is substantially uniform within said microdot.

2. Method according to claim 1, wherein said energy distribution is generated by a light beam, deflected by a deflective mirror device, having an active reflective area of at least 80%.

3. Method according to claim 2, wherein said light beam is guided through projection optics, having an optical transfer function (OTF) value of at least 50% at half the spatial frequency of the mirrors in said deflective mirror device.

4. A system for generating an image on a photosensitive medium, comprising:

a light source;

collimation means for receiving light from said light source and providing collimated light;

spatial light modulation means for receiving said collimated light and for selectively modulating said collimated light;

projection optics for selectively projecting said modulated light;

said spatial light modulation means comprising a plurality of individually addressable elements having an active zone for temporarily directing a light beam towards said projection optics; and

said elements being regularly spaced at a fixed spatial frequency and a filling factor of the active zone of at least 80%.

5. System according to claim 4, wherein said projection optics has an optical transfer function (OTF) value of at least 50% at half said fixed spatial frequency.

6. System according to claim 4, wherein the reflection or transmission of said elements decreases towards the centre of each element.

7. A system for generating an image on a photosensitive medium, comprising:

a light source;

collimation means for receiving light from said light source and for providing collimated light;

spatial light modulation means for receiving said collimated light and for selectively modulating said collimated light;

projection optics for selectively projecting said modulated light;

said spatial light modulation means comprising a plurality of individually addressable elements for temporarily directing a light beam towards said projection optics;

said elements being regularly spaced at a fixed spatial frequency; and

said projection optics having an optical transfer function (OTF) value of at least 50% at half said fixed spatial frequency.