WO1998031137A1

WO1998031137A1 - Image recorder for computer graphics images

Info

Publication number: WO1998031137A1
Application number: PCT/US1998/000742
Authority: WO
Inventors: Mihai C. Demetrescu; Stefan G. Demetrescu
Original assignee: Lasergraphics, Inc.
Priority date: 1997-01-13
Filing date: 1998-01-13
Publication date: 1998-07-16

Abstract

High definition computer-generated graphic images are recorded, as by exposing a photosensitive medium (67) through a mask structure (10) or print-head, which defines an array of spaced apart pixel-sized apertures (12). The pixel apertures are selectively illuminated by a relatively coarse illumination source as a traditional cathode ray tube (32), and in one embodiment, along with a relatively average quality lens. Relative movement is provided between the mask structure and the photosensitive medium to step through a series of discrete positions as arrays of pixels are recorded at each relative position to then collectively construct the desired image. In yet another embodiment, the relative movement is accomplished by controlled displacement of a lens which forms the image of the mask on the photosensitive medium. Various types of mask structures, illumination sources and color graphics recording systems are disclosed using both positive and negative exposure techniques.

Description

IMAGE RECORDER FOR COMPUTER GRAPHICS IMAGES

BACKGROUND AND FIELD OF THE INVENTION The present invention pertains generally to the field of image recording systems for producing pictures, element-by-element with modulated light and involves methods and apparatus for scan producing quality computer graphics images.

A variety of devices, including computer graphics apparatus, are currently used to print light images and provide hard copies of such images. In that regard, cathode ray tube (CRT) displays have been variously used with cameras to obtain both photographic prints and transparencies. For such applications, conventional cameras are capable of high definition; however, images taken from CRT's traditionally have had limited definition.

Generally, conventional CRT displays are accomplished by a modulated electron beam scanning picture elements (pixels) on a screen to excite a phosphor surface. While reducing the cross section of the electron beam that impinges on the phosphor surface increases the definition of pixels, the mutual repulsion of electrons in the beam makes pin point focusing difficult. Consequently, high-resolution pin point CRT displays traditionally have been costly and problematic. As a related consideration, the cost of optical elements used in image recorders usually increases with the degree of definition. Fine focusing also presents a problem in laser graphic imaging, primarily due to imperfections in the optical systems associated with such equipment and the difficulties of precisely modulating a laser beam while it is variously deflected. Accordingly, a need exists for improved methods and systems to record improved graphics images, as from digital data.

SUMMARY OF THE INVENTION

Generally the present invention provides a method and apparatus for optically producing images with improved definition while using relatively coarse illumination sources, such as low cost lenses and low definition CRT display devices. Basically, a relatively coarse source of illumination provides modulated light spots representative of pixel elements (pixels) and the spots are masked to define precise pixels. Collectively, the precise pixels compose a relatively high definition image, as for example on a photosensitive surface. In one embodiment, during a stepwise raster scanning process, pixels on a photosensitive medium are exposed until an image is recorded.

In one embodiment, pixel recording energy is provided as illumination from an electro- optical device defining a screen to provide spots of illumination of a predetermined intensity and duration. A mask structure defines an array of pixel-size holes or apertures that are smaller than the pixel spots or areas of illumination. The mask structure is scanned by spots in a raster pattern to record pixels as the light intensity or dwell time is controlled. Note that, as disclosed in the examples, the distance between any two adjacent apertures in the mask is at least double the distance between any two adjacent lines in the raster pattern. Accordingly, adjacent pixels are never simultaneously illuminated and thus are preserved individually distinct. In a somewhat related way, typically, the total number of apertures in the mask is substantially less than the total number of pixels in a printed image.

In other embodiments, masked structures variously obstruct or control (conform) the light, or other radiant energy, so that only one defined pixel is impinged and exposed at a time on a photosensitive film or paper.

Fields or sets of pixels may be recorded at each of a sequence of positional relationships between the recording medium and the mask structure. In various embodiments, the illumination may be variously controlled for each pixel as with respect to time and/or light intensity. As a result, an image of relatively high quality can be attained pixel-by-pixel, field- by-field in accordance herewith.

Embodiments of the present invention are susceptible to many variations, as for example, regarding the sources of illumination (or excitation) to provide energy, the mask structures to conform the energy, the image recording apparatus and the control system. The system may utilize a single illumination source such as a CRT display device or a laser structure to illuminate individual pixels through the mask structure. Alternatively, a pixel-defining mask structure may include an independently controlled light source dedicated to each pixel element. Also, as disclosed herein, the illumination for a raster image, from a CRT device, may be focused by an array of microlenses, with select portions passing through apertures in a mask structure in the form of a print-head. Thus, the conformation of illumination may involve concentration rather than screening. In accordance with the disclosed embodiments, full color images are obtained by superimposing color-filtered monochromatic images.

In a specific form of one disclosed embodiment, a camera receives components (pixel- by-pixel) of a two-dimensional raster image from a CRT display controlled by a digital computer. The sequence of illumination (raster) for individual pixels is controlled and correlated with displacement of the mask structure relative to the recording medium. That is, for each positional relationship between the mask structure and the recording medium, a set or field of pixels are exposed. Ultimately, the individual fields compose the raster image. Component images may be recorded to accomplish a color representation. In alternative embodiments, various illumination techniques can be used. As disclosed in detail, a mask structure can be positioned adjacent to the screen of a CRT to selectively expose pixels on the recording medium, e.g. photosensitive film in a camera. Alternatively, a lens focuses pixel-forming light spots at a mask structure mounted adjacent a recording medium, e.g. a supported sheet of photosensitive paper, to expose a positive image. A mask structure is disclosed with aperture microlenses to concentrate the illumination for passage through individual apertures. Various other forms and structures will be apparent from the detailed embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is an enlarged fragmentary plan view of a mask structure in accordance herewith illustrating precise pixel recording with course illumination;

FIGURE 2 is an enlarged fragmentary plan view of a mask structure in accordance herewith illustrating an exemplary exposure sequence;

FIGURE 3 is a perspective and diagrammatic view illustrating a recording device in accordance herewith;

FIGURE 4 is a plan view showing an alternative mask structure configuration and illustrating a mode of operation;

FIGURE 5 is a diagrammatic representation illustrating displacement of an exemplary lens in order to displace the image of the mask; FIGURE 6 is a perspective and diagrammatic view of an alternative recording device in accordance herewith; FIGURE 7 is a diagrammatic representation indicative of an exposure sequence as may be utilized in association with the system of FIGURE 6;

FIGURE 8 is a diagram representing an illustrative raster scan sequence as may be utilized in accordance herewith; FIGURE 9 is an enlarged fragmentary view of a mask structure illustrating the use of microlenses; and

FIGURE 10 is a schematic and block diagram illustrating another form of a color recording device in accordance herewith.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

As indicated above, detailed illustrative embodiments of the present invention are disclosed herein. However, elements in accordance with the present invention may be embodied in a wide variety of forms some of which may be quite different from those of the disclosed embodiment. Consequently, the specific structural and functional details disclosed herein are merely representative; yet in that regard, they are deemed to afford the best embodiment for purposes of disclosure and to provide a basis for the claims herein which define the scope of the present invention.

FIGURE 1 preliminarily illustrates the operation of one embodiment hereof for conforming a coarse source of pixel illumination into finer pixel printing illuminations which can be independently varied in intensity or dwell time to create high resolution images.

A small fragment of a light-opaque mask 10 is shown defining an aperture 12, which for example may take the form of a circular hole or transparent opening. As represented, the flat frontal surface of the mask 10 is illuminated with a larger pixel illumination spot 14 indicated by a dashed-line circle. Thus, the mask 10 passes a conformed fragment of the illumination through the pixel aperture 12. The select pixel illumination records a pixel on a medium 16 fragmentarily shown behind the mask 10, which may take the form of a photosensitive plate, film, paper or other recording, printing or registering medium. Thus, a select, conformed portion of the illumination spot 14 is passed through the aperture 12 to record a pixel on the medium 16. To accomplish a composite raster image, the printing of individual pixels is repeated in a sequence, as for example illustrated by the displaced aperture positions 12', 12", and 12'" (represented by dashed line circles) In that regard, relative displacement between the aperture

12 and the medium 16 is provided to sequentially expose pixels at the aperture positions 12,

12', 12", and 12'" The light intensity or illumination dwell time for each pixel is modulated to accomplish the desired pixel exposures Thus, the coarse illumination represented by the spot 14 is precisely defined at individual pixels As indicated in FIGURE 2, the total number of pixel apertures 12 is substantially less than the total number of aperture positions 12', 12",

12'" and so on, each of which depicts a pixel location

To consider an exemplary recording sequence, assume initially that a coarse illumination source provides the spot 14 with the predetermined intensity to illuminate the aperture 12 The illumination continues for a predetermined interval and as a result a pixel is printed on the medium 16 Again, note that the exposure or intensity of recording, can be varied by controlling either the dwell time or the beam intensity

After the initial exposure, the relative position of the mask 10 and the medium 16 is displaced so that the aperture position 12' is active Again, illumination is provided by the spot 14 which may be variously positioned so long as it embraces the aperture position 12

The process is simply repeated for each indicated aperture position 12", 12'" and so on, to record a line of pixels and ultimately a composite raster image

To consider a scanning pattern for the raster image along with a multiple-aperture mask structure, reference now will be made to FIGURE 2 Again, a fragment of the mask 10 is illustrated indicating exemplary positions for an array of apertures T, specifically apertures

TI, T2, T3 and T4 (corners) Other relative aperture exposure positions to conform the light energy are indicated in phantom by dashed lines

As illustrated, the aperture TI coincides with a position xl yl on the medium 16 With movement of the mask 10 relative to the medium 16, as indicated by an arrow A, other positions will be recorded in a line so that ultimately the aperture TI will expose the position x4 yl Thus, as relative displacement occurs in a line-scanning pattern, individual pixels on the medium 16 are exposed in mini-raster patterns For example, in the configuration of FIGURE

2, with pixel-by-pixel movement as indicated by the horizontal arrow A and line-by-line movement as indicated by the arrow B, the aperture TI would expose pixels in sequence at the following locations xl yl, x2 yl, x3 yl, x4 yl, xl y2, x2 y2, x3 y2, x4 y2, xl y3 and so on to y4. Concurrently, all the other apertures, including apertures T2, T3 and T4 as illustrated, are illuminated and will scan and record similar patterns of pixels. Accordingly, each pixel is recorded based on the conformed energy of radiation passed by the aperture, that is the product of radiation intensity and duration of exposure.

In view of the recording process as described above, FIGURE 3 illustrates a system for recording the pixels of a graphic raster image in accordance herewith. A mask structure M in the system of FIGURE 3 conforms pixel illuminations from a display unit D to expose a photosensitive medium in a camera C. The mask structure M includes a mask 10, which may take the form of a planar sheet of opaque material with small apertures 12 defined in the rows and columns of a rectangular array as explained with reference to FIGURE 2. The mask 10 may take the form of a sheet of photographic film that is opaque except for the areas defining the pixel apertures 12. Alternatively, a sheet of opaque material may be perforated, as with a laser, to form the minute, precisely located holes i.e. the pixel-exposing apertures 12. The mask 10 is supported for horizontal displacement within a frame 18 which is mounted for vertical displacement between a pair of vertical rails 20 fixed to a solid support base 22. A horizontal mask driver or actuator 24 is mounted in the frame 18 for displacing the mask horizontally (along an X axis) relative to the frame 18. A vertical mask actuator 26 is affixed to the base 22 (by any suitable means, not shown) and is connected for displacing the frame 18 along the Y axis relative to the base 22.

The mask drivers or actuators 24 and 26 are actuated by circuits 25 and 27 respectively (blocks) and may take the form of electrical stepping motors mechanically coupled to the mask 10 and frame 18 respectively by mask linkages 28 and 30 so as to obtain precise linear displacement of the mask 10. In the system of FIGURE 3, the display unit D incorporates a cathode ray tube (CRT)

32 mounted with its screen 33 adjacent, and substantially coplanar to, the mask 10. Consequently, spot illumination from the CRT 32 is selectively passed through the mask 10 and a filter apparatus 31 to expose film in the camera C. Note that as indicated by a dashed line 37, the base 22, the filter apparatus 31 and the camera are rigidly affixed together as a unitary optical bench structure. Also, these elements are enclosed in an opaque housing, symbolically represented by a dashed line 37, illustrating the obstruction of ambient light from the light elements.

The filter apparatus 31 includes a filter wheel 35 defining four openings, specifically including a clear window 58, a blue filter 60, a green filter 62 and a red filter 64. The filter wheel 35 is variously positioned by a coaxial control motor 56 to align the desired window or color filter angularly with the camera 34 and the mask 10. Generally, in using a monochromatic CRT 32, the clear window is used for black-and-white images while the color filters 60, 62, 64 are employed for repeated exposures to obtain color images. Thus, raster images are recorded on a frame 67 of film (symbolically represented) in the camera C. Operation of the system of FIGURE 3 is controlled by a digital computer 40 (lower center) which supplies control signals to: the mask circuits 25 and 27, a control 51 for the camera 34, the filter control motor 56 and indirectly to the CRT device 32, all as will now be considered.

Note that the CRT device 32 incorporates deflection coils, that is, a yoke 38 and an electron gun structure 41. Essentially, the coils 38 deflect the electron beam to selected impact locations on the screen 33 while the gun 41 provides the beam for a desired time at the desired intensity. Accordingly, the desired locations on the screen are illuminated to provide pixel energy for recording an image.

The deflection yoke 38 is controlled by deflection circuits 52 (horizontal and vertical) coupled directly to the computer 40. Accordingly desired pixel spots are provided. The computer 40 also is connected to a pair of digital-analog converters 44 and 46. The converter 46 is connected through a pulse-width modulator 48 to provide a gating duration signal to an analog coincidence gate 50 that also is connected to receive an intensity signal.

Essentially, the convertor 44 receives a signal I from the computer 40 to specify light intensity while the convertor 46 receives a duration signal W indicative of dwell time. Essentially, the analog intensity signal I is gated for a duration of controlled dwell time (duration signal W). Thus, the desired energy of radiation is provided for printing each pixel.

To obtain two hundred fifty six discrete levels of pixel image intensity, a minimum word length of eight bits is required for storage in the computer 40. However, if alternatively, separate intensity and duration signals are combined as considered above, each of the two signals may be encoded in a 4-bit word, each word yielding sixteen discrete levels for each signal. Thus, the total pixel image luminance levels obtained by combining the two sixteen- level signals also is 256. In any event, as indicated above, under control of stored pixel data, it is possible to utilize various techniques to accomplish the desired energy of radiation for printing individual pixels. The deflection of the beam, as provided by the deflection circuits 52, may be accomplished by staircase voltages so that the impact spot of the beam, and the resulting light spot will dwell at each aperture 12. Accordingly, an opportunity is provided for a desired level of energy or radiation to record each pixel.

In view of the above preliminary explanation of structure and operating components, consider the overall operation of the system of FIGURE 3 in somewhat greater detail. Data required for printing a high-definition raster image is digitally stored in the computer 40. That is, each pixel of the desired image or picture is specified by digital data indicating a mask position (accordingly the vertical and horizontal CRT deflection voltages) and a pixel level. Various image-composing scan patterns, as described above, may be utilized in the system of FIGURE 3 with the mask M being displaced to pass the pixel illumination more precisely (see FIGURE 2). For example, at the beginning, under control of the computer 40, the mask 10 may be positioned at the upper left of its pattern, controlled by the mask circuits 25 and 27.

With the mask 10 in the starting position (FIGURE 2), the computer 40 provides the desired illumination signals I and W for the initial pixel at position xl yl (FIGURE 2). Accordingly, the desired energy of radiation is provided by the CRT display device D and passed through the initial aperture 12 (FIGURE 1) to expose the film in the camera 34, the camera shutter being opened by the camera control 51.

After exposure of the pixel at location xl yl (and other related locations), the beam is deflected and modulated to expose the next pixel locations, e.g. location x2 yl (FIGURE 2, upper right) and so on. Thus in sequence, each set or field of the pixel locations is exposed for a positional relationship between the mask 10 and the CRT screen 33.

Recapitulating to some extent, with the recording of each field of pixels as indicated above, the mask 10 is stepped as illustrated in FIGURE 2 preparatory to exposing the next field. Specifically, the computer 40 actuates the horizontal mask circuit 27 to step the mask 10 one pixel position. Following that motion, the recording process is repeated. The process is thus continued in the pattern as described with reference to FIGURE 2 until the film in the camera 34 has been completely printed with the raster image Note that the camera shutter may remain open throughout the sequential process or opened and closed in sync, under control of the control 51.

In accordance with the above operation, monochromatic images may be recorded on the film 67 in the camera 34. To accomplish such images, pixel illuminations are received by the camera through the clear window 58 of the filter apparatus 31 However, to record color images, rather than to use the clear window 58 as illustrated, additive component exposures are performed with light energy selectively passed through each of the filters, blue 60, green 62 and red 64 Consequently, the additive recording of the component colors results in printing a composite color image

In the creation of color pictures, the color information for each pixel is stored in the computer 40 and correlated data controls the filter wheel 35 by actuating the motor 56 For each color, the mask 10 is displaced through the previously described sequence of positions and pixel apertures 12 are illuminated as appropriate for the picture Turning now to FIGURE 4, an alternative form of pixel-defining mask 70 is illustrated for use in a system similar to that of FIGURE 3 The mask 70 differs from the mask 10 (FIGURE 1) in that the pixel apertures 72 are disposed at an angle to the horizontal axis of translation. That is, horizontals are indicated in FIGURE 4 by dashed lines 71 separated by a vertical pitch as illustrated Pixel apertures 72 are indicated extending diagonally on dashed lines 73 between the horizontals 71 The rows of pixels 72 have a pitch equal to the number of pixel diameters between adjacent pixel apertures lying on a line parallel to the horizontals 71 Thus, the pitch increases as the angle between the pixel rows and the translation axis decreases

In the exemplary pattern of FIGURE 4, the horizontal pitch is twenty four steps or pixel diameters The vertical pitch is the spacing between pixel apertures 72 lying on vertical columns (dashed lines 75) perpendicular to the horizontals 71 (five pixels in this example) The mask 70, as shown fragmentarily, depicts a series of positions (dashed small circles) with respect to a fragment of film 90 in facing relationship with the mask 70 Note that the relative displacement between the mask 70 and the film 90 could be accomplished by the mask 70 moving to the right on a single axis of translation, as indicated by an arrow 74 Accordingly, during sequential field exposures, each of the apertures 72 would expose a partial line in the composite image. The aggregate of all these partial lines thus covers all the pixels of the picture even though the mask is translated along one axis only. Accordingly, a complete black and white picture could be accomplished or alternatively repeated exposures could additively accomplish a color picture as described above. Recapitulating to some extent, it now may be seen that, in order to expose all pixels of an image through a pixel-conforming mask, the image of the mask must be displaced with respect to the recording medium. As disclosed above, this has been accomplished by moving the mask itself along one or two axes, and could also be accomplished by moving the recording medium, as will be explained further below. Consider another way to achieve the mask-image displacement. In FIGURE 5, image of the mask Ml, illuminated as explained above, is formed on the recording medium R by the lens L. When this lens L is moved in a plane parallel with the recording medium, say to position occupied by the lens L', the image moves with it, from image position I to image position I'. Clearly, the lens movement can be along one axis or along two axes. The result is that the modes of exposing the photographic material explained herein can be accomplished by simply displacing the lens and keeping both the mask and the film/paper in fixed positions.

Alternative to the above exemplary systems and formats, another embodiment is depicted in FIGURE 6 and will now be considered. Essentially, pixel illuminations are provided by a CRT unit 100 (top) for projection through a lens 102 to print a positive image directly on photosensitive paper 104 in a web or roll form. As described above, selectivity in recording is accomplished by a print-head 106 which functions as a mask to conform the pixel illumination somewhat as described above. Note that the print-head 106 lies substantially in the focal plane of the lens 102 and is in contact with the paper 104. As treated in greater detail below, with reference to FIGURES 7 and 8, the apertures in the print-head are spaced apart to avoid spot overlap and the total number of apertures is substantially less than the total number of pixels embraced by the print-head.

Considering the system of FIGURE 6 in greater detail, the recording components again are housed in an opaque enclosure represented by a dashed line 108. Consequently, ambient light is suppressed. External of the enclosure 108, control apparatus 1 10 provides operating signals. Generally, the control apparatus matches the photographic exposure of individual pixels in a raster image with the (electronic) raster information received for printing the image during the relative displacements between the print-head 106 and the paper 104

Returning to the operating components within the enclosure 108, the CRT unit 100 includes a cathode ray tube 112 with a deflection yoke 114 and an internal beam modulation element, e g electron gun 116 (mounted within the tube neck). Accordingly, as disclosed in greater detail below, the CRT unit 100 is controlled by the apparatus 110 to accomplish the desired display on the screen or face 118 of the CRT 112.

As indicated above, individual pixel illuminations appearing on the CRT face 1 18 are focused by the lens 102 to the plane of the print-head 106 (shown grossly exaggerated in thickness). Accordingly, individual apertures (not shown in FIGURE 6) of the print-head 106 pass selective portions of the illumination to conform the energy and print individual pixels on the photosensitive paper 104, constituting the medium in the embodiment of FIGURE 6

As explained above, either monochromatic or color images may be accomplished and in that regard, a filter 120 is illustrated adjacent the lens 102 to accomplish component color illuminations. Of course, various forms of an automated filter structure may be provided somewhat as illustrated in FIGURE 3

Also, as explained above, to print an image, the paper 104 is moved relative to the print-head 106 Note that movement may be continuous or intermittent so long as the apertures are aligned with the select pixels during the recording interval In the embodiment of FIGURE 6, the paper 104 takes the form of a web driven from a roller 122 to a roller 124, thus passing under the print-head 106. Essentially, the roller 124 draws the web of paper 104 from the roller 122 over a platen 126 in synchronism with pixel illuminations. In that regard, the operation of the print-head 106 is treated in detail below Summarily, it conforms pixel energy to print the raster image on the paper 104. A two dimensional array of individually controlled light spots is provided, as where there is at least one spot on each line of a raster and where the distance between any two adjacent spots is at least double the distance between any two adjacent lines in the raster. Accordingly, selectivity is accomplished with conformation without overlap.

Considering the control function, the apparatus 1 10 includes a computer 128 coupled to receive image signals from a raster data source 130 In that regard, the source 130 may take any of a variety of storage forms as mentioned above for providing pixel signals in a coordinated-format raster as disclosed in detail below and utilizing techniques as well known in the computer graphics field.

The computer 128 accomplishes control functions through deflection drive circuits 132 and a pixel image data circuit 134. The deflection drive circuits 132 are connected to the deflection yoke 114 of the CRT 112 for accomplishing the desired raster scan pattern. The pixel data circuit 134 is connected to the electron gun 116 to modulate beam intensity (or duration) and accordingly the light energy of the illumination spot that is projected from the tube face 118 through the lens 102 and the print-head 106 onto the paper 104. The computer 128 precisely controls movement of the paper 104. In that regard, a connection is provided from the computer 128 to a drive motor 136 which is mechanically coupled to the roll 124. Motion of the paper 104 is monitored by a sense roller 138 engaging the paper 104 above the platen 126. The roller 138 is mechanically coupled to a motion sensor 140 which in turn is electrically coupled to the computer 128 for feedback control. Accordingly, the illumination and displacement are precisely synchronized to accomplish the sequential pixel exposure, for example as disclosed below.

In accordance with one embodiment, and as previously suggested, the motion of the paper 104 is upward and to the right as indicated by an arrow 142 (on the paper 104). Consequently, images are recorded pixel-by-pixel and field-by-field somewhat as described above. Initially, consider a simplistic illustrative recording operation involving one mask area with a single group of only four pixels as represented in FIGURE 7.

Generally, a section 150 (FIGURE 7) of the paper 104 (FIGURE 6) is shown at a series of different times TI, T2, T3, T4 and T5 as it progressively moves under a simplistic mask structure 152 defining columns of nine pixel apertures A (designated by number as shown). Note that the apertures extend diagonally down and across the mask structure 152 and are relatively displaced vertically (center to center) by a distance double the distance between horizontal lines Yl - Y7. The apertures A in mask 152 are thus arranged in vertical columns Cl - C9, fragments of three being illustrated, i.e. Cl, C5 and C9. For easier explanation, the paper section 150 will be described to move in the direction of the arrow 142 under the mask 152 in steps, each step advancing it one raster line. Consider the operation as sequentially depicted at the times TI - T5 whereby light spots S (position numbered) are conformed to print pixels of an image on the paper section 150.

With the paper section 150 and the masking structure 152 positioned as indicated at the time TI, apertures A4 on line Yl are illuminated by light spots S4, each as represented by a dashed line circle. Accordingly, pixels (represented by an "X") are recorded on the paper 150 at the current positions of the apertures A4. From this point, pixels previously printed on paper 150 and which lie under the opaque parts of mask 152 will be shown as lighter "X"s for ease of explanation.

As the process continues, to keep the drawings legible, at the time T2, the paper section 150 is shown to have advanced two steps to Y3 (which equals two raster lines). Thus, the pixels exposed at TI are now on line Y3. Of course, in the meantime pixels on line Y2 were exposed. At the time T2, pixels under apertures A3 and A4 on lines Yl and Y3 are now being exposed (recorded), each with the proper intensity as dictated by the computer.

At the time T3, the paper section 150 has advanced two more steps. As shown, all pixels on column X4 and X8 have been previously exposed on lines Y2 - Y5, and the pixels on lines Yl, Y3 and Y5 are now being exposed (time T3) as a result of spots of light S visiting apertures A2, A3 and A4 on these lines.

Time T4 depicts the configuration after two more steps with the light spot S visiting apertures on line Y7 to expose the underlying pixels. At this time spots S also visit all other shown apertures (on lines Yl, Y3 and Y5). It is noteworthy that at time T4, each of the apertures A has exposed a column of pixels (XI - X9) all at the proper raster spacing, even though the mask apertures A do not cover all pixels at any single time.

At the time T5, again two steps later, all pixels on the top line have been exposed (as they were at T4) and have advanced beyond the top of mask 152. From that point forward, the picture continues to be recorded with paper section 150 advancing one step (or line) at a time and all apertures A in mask 152 being illuminated at each step with the appropriate intensity under the control of the computer.

It is to be appreciated that, conceptually as described, after each step-advancement, the paper stops long enough for the CRT 100 (FIGURE 6) to produce sequentially the spots of light S necessary for illumination of all apertures in the mask 152. However, in a different embodiment, the movement of the paper under print-head 106 is continuous, because the exposure time of all pixels under apertures A is so relatively short that no appreciable difference can be seen in the picture recorded (even though it exists - for example each 12" line is tilted 1/400" or .0025" in one embodiment).

Proceeding from the positional relationship as indicated at T5, the image is recorded pixel-by-pixel, row by row to emerge from the mask structure 152. Of course, various masks and scanning patterns may be utilized with various pixel and field arrangements. For example, note that with respect to the exposure pattern explained with reference to FIGURE 7, various electron beam scanning patterns may be utilized to attain the desired exposures. Even though the pixels on each line of the conventional raster which is printed on the paper are not exposed in sequence on that line, it will now be apparent that the important operation is that all pixels of the raster-image stored in the computer be exposed on paper. The order in which they are exposed is not relevant as long as they are all exposed with the proper intensity and dwell time. Also, the simple aperture pattern of the masking structure 152 can be replicated to define larger fields. A field is defined here as the aggregate of all pixels exposed (recorded) on the photosensitive medium when all apertures of the print-head are illuminated once, each with the proper intensity. In that regard, a large-field structure for the print-head 106 (FIGURE 6) will now be considered.

FIGURE 8 shows two horizontally aligned end fragments of a sheet mask structure 160. The structure is opaque and defines pixel apertures A aligned in horizontal rows and extending diagonally in the vertical direction. Each column of pixels, e.g. the column of pixels Al 1 - A161 embraces a sweep area E. Thus, the columns respectively print areas El - En.

The FIGURES 7 and 8 illustrate a placement of the apertures A in the mask structure in relation to a print medium. Specifically, the distance between adjacent pairs of apertures A passing illuminations is at least twice (and usually much more than) the distance between adjacent lines of the raster image. Thus, overlap printing is avoided. As another consideration, the total number of apertures A in the mask structure is substantially less than the total number of pixels embraced by the mask. Of course, a simpler mask structure results.

Recapitulating to some extent, in the exposure of a medium, as described above, the medium, e.g. paper, is moved under the mask structure 160 as explained with respect to FIGURE 7. As indicated, depending on relative speeds and timing, movement can be stepped or continuous. Synchronized with the relative displacement, the CRT unit 100 (FIGURE 6) scans a raster pattern which is projected (pixel-by- pixel) through the lens 102 onto the print- head 106 having a detailed form as represented in FIGURE 8. The raster scan pattern is illustrated in FIGURE 8 by a series of horizontal scan lines 165. That is, the scan lines 165, defining a raster pattern 166, are swept by the deflection yoke 114 (FIGURE 6). However, the intensity of the beam, and the resulting intensity of light (and duration) illuminating a particular pixel to provide a specific quantity of energy is modulated in accordance with the value stored for the pixel in the raster data source 130 (FIGURE 6). With respect to the production of a color image as explained above, representations are stored for each pixel for each component color. Thus, the additive light energy provided through the pixel apertures records or prints the desired pixel color and intensity. Thus, in conjunction with 3 color filters, the raster pattern 166 (FIGURE 8) scans the pixel apertures, row by row in a repeating pattern. Specifically, as illustrated, the scanning proceeds aperture-to-aperture as follows: Al 1, A12, A13, and so on to Aln. Then, moving to the next row the scanning proceeds in a reversed direction, A_2n, A_2n._!, and so on A₂₁ as illustrated by the scan lines 165.

With the completion of the first raster scan, all of the pixel apertures A have been visited, affording each an opportunity to pass illumination and print a pixel. At that point, the recording medium, e.g. photosensitive paper 104 (FIGURE 6) is displaced upwardly as discussed with reference to FIGURE 7 and another raster pattern 166 (field) is scanned. Consequently, pixel-by-pixel, line-by-line and field-by-field, the image is printed. Note that in one operating format, the recording of an image may be initiated by first illuminating the pixel aperture Ann (lower right) as described with respect to FIGURE 7.

Generally, in accordance with the embodiment of FIGURES 6-8, pixel data is stored in a virtual memory array related to the array of the mask structure 160. Consequently, the computer 128 (FIGURE 6) addresses the raster data source 130 to provide sequences of pixels, modulate the beam intensity (and/or duration) accordingly and coordinates illumination of pixel apertures to conform the light and thus print the desired image.

As explained above, the CRT unit 100 (FIGURE 6) and the lens 102 are afforded substantial tolerance in illuminating the print-head apertures A (FIGURE 1) as the mask structure affords conformed pixel printing. However, in some instances, it may be desired to increase the illumination of pixels for printing. Such an increase is afforded by an alternative form of mask structure to conform pixel illumination as will now be considered with respect to FIGURE 9.

A grossly enlarged fragment of the alternative mask structure is shown to include a perforated opaque sheet 170 which may be formed of metal Bonded to the sheet 170 is a light-passing lens layer 172 defining lens elements (microlenses) 174 above each of the apertures 176 in the sheet 170 (similar to the apertures A in FIGURES 7 and 8).

As explained above and shown in FIGURE 9, the illumination spots S are substantially larger than the apertures A (e.g aperture 176) with a consequence that an illumination spot S may encompass an entire microlens element 174 or at least a substantial part of it Each element 174 then concentrates the received illumination to pass through the aperture 176, thus intensifying the pixel illumination Accordingly, substantially increased intensities of illumination are afforded while conforming the illumination for printing pixels

In yet a slightly different embodiment, the opaque layer or sheet 170 (FIGURE 9) with apertures 176 is eliminated because microlenses 174 concentrate the light of spot S so efficiently that they effectively form small spots practically identical with those formed by a mask with the apertures Thus, a lesser structure is provided Yet in conjunction with a high- contrast photosensitive medium (such as photographic print paper), there is little difference between exposing with or without layer 170, because light passing through areas other than the microlenses is too weak to expose the paper Therefore, the methods of exposing paper through a print-head disclosed hereabove are directly applicable to a print-head containing only microlenses, in arrangements similar with, or identical to, those previously described

Another embodiment of the system is illustrated in FIGURE 10 and will now be considered Generally, the system of FIGURE 10 provides color prints

Considering the system of FIGURE 10 somewhat generally, an illumination source 210 provides three different color images (green, red, blue) simultaneously to illuminate pixels on a web of medium 212 supported by a medium support 214 and mask head structure 218 Generally, the medium support and masking head 214 may take a form as described with respect to FIGURE 6

The illumination source 210 incorporates three cathode ray display units symbolically represented as a blue unit 226, a green unit 228 and a red unit 230 As suggested above, each of the CRT display units 226, 228, and 230 provides a component color display to simultaneously print the pixels of an image.

Images from the orthogonally positioned display units are oriented to a common axis indicated by a line 232 for projection onto the medium 212. The alignment is accomplished by a pair of dichroic beam splitters 234 and 236. Thus, illumination from the green unit 228 passes through the beam splitters 234 and 236 with very little loss, to present an image in the plane of the recording medium 212. To accomplish a similar alignment, illumination from the blue unit 226 is reflected from the splitter 234 to pass through the splitter 236. Finally, illumination from the red unit is reflected from the splitter 236 to accomplish similar alignment. Accordingly, the component illuminations are projected by a lens 216 simultaneously to print the medium 212. In that regard, a CRT drive 239 and control computer 240 separately energize the units 226, 228 and 230 to provide pixel illuminations as described above. Specifically, intensity, time and displacement are involved, again as explained above. In that regard, the drive 239 is in turn controlled by the control computer 240. Further, the principles of conforming the spots to impinge the photosensitive medium are incorporated by the utilization of a mask structure as described above.

Of course, as will be apparent from the above, a large variety of system formats may be employed in accordance herewith, several relating to various mask structures. For example, mask structures might be variously integrated with a CRT display. For example, phosphor coating on the interior surface of the CRT (normally deposited in a continuous coating) might be deposited in pixel-sized spots layed and spaced in a manner analogous to the disposition of the pixel apertures in the mask as discussed above.

As another exemplary alternative, a continuous phosphor coating might be applied to a CRT screen and an electron beam mask might be provided between the phosphor coating and the electron gun so that the beam is allowed to impact (reach) the phosphor coating only at the desired pixel element locations.

As another consideration, the source of pixel illumination may take various forms other than CRT displays. For example, a laser may be used to illuminate a mask structure somewhat as described above by deflecting and modulating the laser beam with suitably controlled optical means. As a further variation of the invention, the illumination source may be integrated with the pixel elements. Thus, a combined mask/illumination source may take the form of a planar array of light-emitting elements which are either inherently pixel sized or masked to produce pixel-size light sources disposed in a manner similar to the elements as discussed above. Such light-emitting pixel elements might take the form of very small, or masked, light-emitting diodes.

As still another variation of the system, a pixel-defining mask may be illuminated through a planar array of light-valve elements, such as liquid-crystal devices, the entire array being back-lighted, for example, by a flood light source. The state of each light-valve element (i.e., opaque or more or less translucent) may be individually controlled by suitable switch circuits. The dimensions of each spot of light produced by the light valving array is greater than those of the pixel elements defined in the mask but less so than the distance between any two adjacent pixel elements to thereby avoid illumination simultaneously of any two adjacent pixel elements by the same light-valving element as explained above. Thus, the light -valving array in its opaque state serves as a screen to shield the light-defining screen from the flood light source except where light is allowed to pass by a light-valving element in its more or less transmissive state. By controlling the state of individual light-valving elements, all pixels in a field are exposed, then the photosensitive medium moves and the next field is exposed, to eventually form the whole image. While several embodiments of the present invention have been described, it will be apparent from the foregoing disclosure that many departures, alterations and substitutions are possible without departing from the spirit or scope of the present invention which is defined in accordance with the following claims.

Claims

WHAT IS CLAIMED IS:

1. A recorder for a raster image, comprising: a source of pixel energy to manifest select individual pixels of said image; a record medium support to provide a photo-sensitive recording surface protected from ambient light or radiation; a mask for conforming said pixel energy to impinge said recording surface at discrete individual pixel-sized locations; and a control unit for operation with respect to: said source, said recording medium support and said mask in order to successively position the image of said mask with reference to said recording surface, and in cooperation with said source of pixel energy to record pixels in accordance with said raster image.

2. A recorder according to claim 1 wherein said source of pixel energy comprises: a screen for providing a two-dimensional array of pixel illumination energy and wherein said mask conforms said pixel illumination energy by defining apertures in an opaque sheet such that the distance between adjacent pairs of illuminations impacting said recording surface is at least twice the distance between adjacent lines of said raster image.

3. A recorder according to claim 2 wherein said source of pixel energy comprises: a lens element to focus said pixel illumination energy on said mask.

4. A recorder according to claim 1 wherein said source of pixel energy comprises: a light producing electro-optical device defining a display screen to provide spots of light of predetermined intensity and duration driven by said control unit, in accordance with said raster image.

5. A recorder according to claim 2 wherein said source of pixel energy comprises: a cathode ray tube image display unit.

6. A recorder according to claim 5 wherein said cathode ray tube image display unit includes a plurality of cathode ray tube devices for providing a plurality of color component images and at least one dichroic beam splitter.

7. A recorder according to claim 5 wherein said source of pixel energy comprises: a deflection means to deflect the beam in said cathode ray tube image display unit to successive positions to illuminate said apertures and exposure means to control the intensity and duration of said illumination in accordance with said raster image.

8. A recorder according to claim 1 wherein said source of pixel energy comprises: a screen for providing a two-dimensional array of pixel illuminations and wherein said mask conforms said pixel illuminations by defining apertures, the total number of apertures in said mask being substantially less than the total number of pixels eventually recorded through said mask.

9. A recorder according to claim 1 wherein said source of pixel energy comprises: a screen for providing a two-dimensional array of pixel illuminations and wherein said mask conforms said pixel illuminations by defining apertures, the total number of apertures in said mask being substantially less than the total number of pixels in said raster image.

10. A recorder according to claim 1 wherein said mask comprises: an opaque layer defining a plurality of energy conforming apertures and wherein said apertures are such that the largest dimension thereof is less than the distance between the centers of any pair thereof.

11. A recorder according to claim 1 wherein said mask comprises: an opaque layer defining a plurality of energy conforming apertures and wherein said apertures are such that the total number thereof is substantially less than the total number of pixels eventually recorded through said mask.

12. A recorder according to claim 1 wherein said mask comprises: an opaque layer defining a plurality of energy conforming apertures and wherein said apertures are such that the total number thereof is substantially less than the total number of pixels in said raster image.

13. A recorder according to claim 12 wherein said mask is located contiguous to said source, and which further includes a lens element to focus said energy conforming apertures on said recording surface.

14. A recorder according to claim 13 wherein said lens element includes a lens and means for displacing said lens controlled by said control unit.

15. A recorder according to claim 11 wherein said mask is located contiguous to said source, and which further includes a lens element to focus said energy conforming apertures on said recording surface.

16. A recorder according to claim 15 wherein said lens element includes a lens and means for displacing said lens controlled by said control unit.

17. A recorder according to claim 10 wherein said mask is located contiguous to said recording surface.

18. A recorder according to claim 2 wherein said mask includes an array of microlenses focused respectively on said apertures.

19. A recorder according to claim 1 wherein said mask consists of an array of microlenses, each focused on said recording surface.

20. A recorder according to claim 19 wherein the number of said microlenses is substantially less than the total number of pixels in said raster image.

21. A recorder according to claim 19 wherein the distance between the centers of any pair of said microlenses is longer than the size (diameter) of the spots of light focused by them on said recording surface.

22. A recorder according to claim 20 wherein said source of pixel energy comprises a screen for providing a two-dimensional array of pixel illumination energy.

23. A recorder according to claim 22 wherein said source of pixel energy also comprises a lens to project said array of pixel illumination energy on said microlenses.

24. A recorder according to claim 18 wherein said microlenses are supported by a layer of defining transparent material.

25. A recorder according to claim 10 wherein said mask defines said apertures in at least one angularly offset array.

26. A recorder according to claim 18 wherein said mask defines a plurality of angularly offset rows or columns.

27. A recorder according to claim 1 wherein said recording medium support comprises: a camera.

28. A recorder according to claim 1 wherein said recording medium support comprises: a web structure controlled by said control unit for successively exposing a photosensitive medium to receive said image.

29. A recorder according to claim 1 wherein said source of pixel energy comprises a multi-color structure for providing component color energy.

30 A recorder according to claim 1 further including a filter structure for filtering a plurality of component color images from said source of pixel image to record a color image

31 A recorder according to claim 30 wherein said filter structure includes a plurality of component color filters

32 A recorder according to claim 31 wherein said filter structure further includes a filter positioning holder controlled by said control unit.

33 A recorder according to claim 1 wherein said control unit comprises means to match the exposure energy by said source of pixel energy with pixel values in said raster image

34 A recorder according to claim 33 wherein said control unit comprises a computer for providing raster data representative of said image and control signals for said source, as well as for said record medium support and said mask positions

35 A recorder according to claim 34 wherein said control unit comprises recording medium support and mask control for changing the relative position of said recording surface with reference to said mask to enable recording at all pixel locations of said raster image.

36. A process for printing raster images on a photosensitive medium including the steps of: providing digital pixel signals representative of individual pixels in said raster image; selectively converting said pixel signals to pixel radiant energy for providing select pixel illumination spots, supporting said medium, masking said medium to conform said pixel illumination spots to pixels on said medium, the distance between the pairs of said conformed illuminations impacting said medium being at least twice the distance between adjacent lines in said raster image.

37. A process for printing raster images on a photosensitive medium including the steps of: providing digital pixel signals representative of individual pixels in said raster image; selectively converting said pixel signals to pixel radiant energy for providing pixel illumination spots in a raster; supporting said medium; masking said medium to conform said pixel illumination spots to pixels on said medium, said masking defining apertures of a number substantially less than the number of pixels embraced at any time by said masking.