Exposure apparatus

Abstract: An exposure apparatus, which is responsive to exposure data for controlling the duration of exposure action of an exposure means (4) to reproduce gradations on a photosensitive material, has a converter means (63) responsive to exposure data for determining the compensated duration of exposure action with reference to predetermined characteristics. An exposure controller means (6) controls the exposure means according to the compensated duration of exposure action.

Description: The present invention relates to an exposure apparatus for use in a photographic printer and more specifically, to a digital exposure apparatus provided with an electronic control shutter such as a line exposure shutter. Conventional digital exposure apparatuses with line exposure shutter are known in which each sheet of photosensitive material is moved forward and backward more than one time for exposure to blue, green, and red colors (referred to as B, G, and R hereinafter) in response to the application of corresponding voltages to groups of line exposure elements. In the exposure action, each dot is printed in a color determined by exposure data. As the exposure data includes a gray scale, the exposure is determined by gray levels of the data. It is known to determine the exposure by controlling the duration of the application of voltages to the line exposure elements. If 32 of the gray levels, for example, are required, the duration of the voltage application to the line exposure elements is classified into 32 different modes as shown in Table 1. Table 1 illustrates some of the gray levels; 0, 1, 2, 4, 8, and 16. However, the duration of the application of a voltage to a corresponding line exposure element includes a rise time tl from zero to a given level of intensity after starting the application and a decay time t2 starting when the voltage is interrupted and finishing when the intensity of exposure light is dropped to a disable level, as shown in figure 6, and thus will hardly be proportional to the exposure. Also, the intensity of exposure light is not proportional to the density of a color. It was found that two or four times the intensity of light did not cause the color density to increase directly to a two or four times greater level. It is now understood that the gray levels are hardly produced at high quality by controlling the duration of the application of voltages to the line exposure elements in proportion to corresponding data. A printer, in which exposure duration can be varied, is known from document EP-A-0 421 712. It is an object of the present invention to provide an apparatus capable of controlling the duration of the application of voltage to line exposure elements in proportion to the gray levels of a color to produce a gentle gradation of the color. Accordingly, the invention provides an exposure apparatus for use in a photographic printer and responsive to exposure data for controlling the duration of an exposure action of a light source, of comprising an exposure control means characterised by an electronically controlled shutter, and characterised in that said exposure control means is adapted for controlling the duration of the exposure action of the electronically controlled shutter, and characterised by a converter means responsive to exposure data defining a gray scale, for determining compensated exposure action duration data, with reference to predetermined characteristics of the electronically controlled shutter, and in that said exposure controller means controls the duration of the exposure action of the electronically controlled shutter according to the compensated exposure action duration data, wherein the converter means compensates for a non-linear relationship between the duration of application of an exposure voltage and the resultant exposure. It is noted that the data of a compensated duration of exposure action with reference to predetermined characteristics is not proportional to the exposure action. Further the converter means may comprise, a conversion table in which each item of exposure data refers to a compensated exposure action duration defined by said predetermined characteristics, and means for selecting the data of the compensated exposure action duration by referring to the exposure data in the conversion table. Further, the converter means may comprise a conversion table as defined in claim 3. Further, the converter means may comprise a conversion table as defined in claim 4. Further, the converter means may comprise a conversion table as defined in claim 5. Further, an exposure apparatus of the present invention may further comprise a conversion data setting means as defined in claim 6. In the apparatus according to the invention, the predetermined characteristics can thus be utilized to compensate a delay of the exposure action in the exposure means caused by the rise and decay times. According to a preferred embodiment, a nonlinear relation between the intensity of exposure light and the density of color can be corrected, allowing a desired gray level of the exposure data to be correctly reproduced. Also, according to a preferred embodiment, a conversion table is provided, in which fewer compensated exposure action durations are defined. A desired compensated exposure action duration for reproducing a desired gray level can be calculated from a combination of durations stored in the conversion table. BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 is an overall schematic view of a photographic printer provided with an exposure apparatus according to the present invention; Fig.2 is a schematic view showing a primary part of the photographic printer; Fig.3 is a diagram explaining steps of exposure process; Fig.4 is a block diagram of a primary part of the photographic printer; Fig.5 is a flow chart showing the exposure process; Fig.6 is a waveform diagram of a PLZT element; Fig.7 is a graphic diagram showing a major characteristic of the PLZT element; and Fig.8 is a block diagram of a primary part of a exposure means having TFT color liquid crystal. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT One embodiment of an exposure apparatus of the present invention installed in a photographic printer will be described referring to the accompanying drawings. Fig.1 is an overall schematic view of the photographic printer and Fig.2 is a schematic view of a primary part of the same. As shown in Fig.1, there are provided a magazine 1 for supplying a sheet of a photosensitive material or print paper 2, a negative exposure station 3 for exposing the print paper 2 to optical images of a negative film, a line line-exposure station 4 for exposing the same to digital images, a development unit 5 for developing the exposed print paper 2, a line exposure controller unit 6, and a transfer mechanism 7 for conveying the print paper 2 lengthwisely by a frame-by-frame basis and a dot-by-dot basis. The line exposure controller unit 6 comprises a time controller 61 for controlling the duration of exposure action in the line exposure station 4, a voltage controller 62 for controlling the applying voltage in response to the location of a disk 13, and a transfer controller for controlling the transfer mechanism 7 for conveying movements at given timings, as shown in Fig.4. The time controller 61 includes a converter means or circuit 63 and a PLZT controller means or circuit 64. The converter circuit 63 has such data for conversion as shown in Table 2 in which the gray levels D are defined by applying durations T of a nonlinear function. The gray level data D are determined so that they are proportional to the density of color. The PLZT controller circuit 64 is provided for applying a given voltage to a group of PLZT elements for the duration T. For example, the gray level D=1 in Table 2 is determined by a duration T=t, an intensity of exposure light S=s, and a density of color V=v and if D=2 is requested, the voltage is applied for a duration t2 to have a density v2=2xv. The duration T and the exposure light intensity S are nonlinear functions of the gray level D so that a gray level proportional to the density of color is produced when light of the intensity S has been irradiated for the duration T. If a different type of the photosensitive material of the print paper 2 is used, the voltage applying duration data in Table 2 are modified corresponding to the type. This allows the color density to be consistently produced corresponding to its gray level data, yielding a precise tone. In the negative exposure station 3, an image on the negative film 32 is projected by irradiation of a lamp 31 and focused by a lens 33 on to the print paper 2. As shown in Figs.1 and 2, the print paper 2 is again exposed in the line exposure station 4 to an optical pattern of dots of digital data which has been scanned and recorded with a scanner or produced by an electronic apparatus such as a computer. The digital data consists mainly of the R, G, and B separate color data and the gray level data of each color. The digital data may be introduced in the form of a serial signal to the line exposure controller 6 where it is converted into a parallel data applied to each PLZT element. The parallel data consists of a color data and a gray level data. The color data is fed to the voltage controller 62 and the gray level data is transferred to the time controller 61. The line exposure station 4 comprises an exposure means or PLZT shutter 41 having rows of PLZT elements 44, each row extending widthwisely of the print paper 2, a bundle of optical fibers 42 coupled at one end to the PLZT elements 44 of the PLZT shutter 41 respectively, and a PLZT light source 43 for emitting B, G, and R modes of exposure light through the optical fibers 42. It should be understood that the ratio of number between the PLZT elements 44 and the optical fibers 42 is not limited to 1:1. An intensity of light emitted from the lamp 11 is directed through a mirror tunnel 12 to the disk 13 which comprises three, R, B, and G, color filters, each extending through 120 degrees, R, B, and G modes of light passed through the disk 13 are then transmitted through the optical fibers 42 to corresponding groups of the PLZT elements 44. The PLZT elements 44 are energized with a given amplitude of voltage which is determined by the voltage controller 62 in response to the location (B, G, R modes) of the disk 13 controlled by the gray level data timing the rotation. As the result, a desired mode of light having a specific wavelength is allowed to pass from the optical fibers 42 to the print paper 2. The timing of rotation of the disk 13 is measured by a sensor 15 reading a mark 14 on the disk 13. The three filters of the disk 13 are arranged so that the B, G, and R modes run in this order across an optical path of the bundle of the optical fibers 42. The mark 14 is located between the B and G color filters and the sensor 15 is disposed 120 degrees out of phase with the optical path of the fibers 42. The timing of exposure to the B, G, and R modes of light will be explained referring to Figs.2, 3, and 5. It is assumed that the action starts with Step S1 where the mark 14 is detected by the sensor 15. As it is true that the B mode filter runs through 120 degrees from then, the voltage applied to a target group of the PLZT elements 44 is shifted to 45 volts of a B mode amplitude by the voltage controller 62 in the line exposure controller unit 6 at Step S2. When the exposure to an original pattern of dots of the B mode light has been conducted for a duration proportional to a gray level of its original color pattern data, a row of print dots D1, D2... appear at the gray level on the print paper 2, as shown in Fig.3(A). It is judged that when the disk 13 has rotated another 120 degrees after detection of the mark 14, the filter is turned to the G color mode. Then, the voltage is shifted to 50 volts of a G mode amplitude by the voltage controller 62 in the line exposure controller unit 6 and applied to another group of the PLZT elements 44 for a duration proportional to the gray level of an original color pattern data. Accordingly, the pattern of dots D1, D3... appear on the print paper 2 representing the gray level of its original color pattern as shown in Fig.3(B). Equally, when the disk 13 has rotated further 120 degrees, it is found that the filter is turned to the R color mode. Then, the voltage is shifted to 55 volts of an R mode amplitude by the voltage controller 62 in the line exposure controller unit 6 and applied to a further group of the PLZT elements 44 for a duration proportional to the gray level of an original color pattern. Accordingly, the pattern of R color dots D1... appear at the gray level on the print paper 2 as shown in Fig.3(C). During the above exposure action, the dot D1 is exposed to three, B, G, and R, colors of light, the dot D2 is exposed to two, B and R colors, the dot D3 is exposed to a G color, and the dot D4 is exposed to no color. The exposure duration for each dot is determined by the time controller 61 according to the conversion data listed in Table 2, whereby the gray level of its color pattern data will be produced correctly. The duration of the voltage application to the PLZT elements of each color is controlled so that the color density is proportional to a gray level data, reproducing a desired gradation of the color. During the exposure action of the B, G, and R colors, the print paper 2 remains stalled and allows a widthwisely extending row of the dots to be printed thereon. After a series of the steps shown in Fig.5 is completed, the print paper 2 is then advanced by a distance of one dot size. The exposure position on the print paper 2 is now as shown in Figs.3(D) to 3(F). The same action is then repeated with another group of B, G, and R data being introduced in synchronization with the rotating action of the disk 13, producing another row of dots. Similarly, the print paper 2 is advanced again by the one dot distance upon completion of the exposure action. In this manner, as the print paper 2 is moved lengthwisely, rows of the dots are printed by a sequence of the exposure actions. In the development unit 5, the print paper 2 exposed at the negative exposure station 3 and/or the line exposure station 4 is subjected to a development process and cut into frames before discharged. The 120-degree rotating action of the disk 13 may be timed by pulses to the stepping motor, action of a rotary encoder, or markings arranged at intervals of 120 degrees. The conversion list in Table 2 may be replaced with a conversion list shown in Table 3 where the duration of voltage application T is determined so that the gray level D is proportional to the intensity of exposure light S. In Table 3, the duration of voltage application T is a nonlinear function of the gray level D. Although the color density on a photographic material is a nonlinear function of the intensity of exposure light and not precisely proportional to the gray level in real actions under the conversion with Table 3, it may create no serious problem. The advantage is that the conversion table needs not to be modified depending on a type of the photosensitive material. The duration of voltage application may be prepared only six different lengths of time; t1, t2, t3, t4, t5, and t6. Then, their combinations are assigned to 32 gray levels; for example, D=13 (=8+4+1) is related to T=t5+t4+t2. Also, it is a good idea to set the durations t1, t2, t3, t4, t5, and t6 independently from each other so that a more smooth, precise gradation is reproduced. It is noted that the data of the compensated duration of exposure action referred to in Claims coresponds to the duration of voltage application when PLZT elements are used as exposure means, but in case any other exposure means is used in the procedure, it corresponds to the data in each of the exposure means. The exposure means is not limited to the PLZT elements but may be such an exposure means using a liquid crystal shutter. Further, the exposure means is not limited to the one-dimentional arrayed exposure elements but may be two-dimentional arrayed exposure elements or a system with an exposure head provided with a pair of exposure elements arranged for mechanical scanning action. The light from the light source may be guided to the exposure means by a set of reflector mirrors rather than the optical fibers or the light source itself may be located adjacent to the exposure means. One example of an exposure means employing color liquid crystal shutter is an exposure means utilizing techniques in the field of TFT(Thin Film Field Effect Trangistor) color liquid crystal and the exposure means is described with reference to Fig. 8. Amorphous silicium TFT is formed on a glass base by using a process of semiconductor integrated circuit to form TFT array base 81. Each TFT element f corresponds to a dot to form a transparent electrode driving liquid crystal. Color filter base 82 which is colored into any of RGB according to each dot faces to the TFT array base 81. Liquid cristal 83 is enclosed between the color filter base 82 and TFT array base 81. Transparent common electrode 84 is formed all over the surface of the color filter base 82. Polaraizing plate 85 is provided on the color filter base 82 and a photosensitive material 87 is formed further thereon. Beneath the TFT array base 81, a polarizing plate 86 is provided and is lighted by the light applied by a white light source (not shown). Once TFT elements f are driven, electric charge is stored between the dot electrode and the common electrode 84 and the liquid crystal 83 between thereof is set up to transmit the light. Thereby, predetermined color is exposed to the photosensitive material 87 corresponding to each color filter. Although the exposure apparatus of the present invention is described for use in a photographic printer, it is applicable to any photosensitive material to be exposed.

Claims: An exposure apparatus for use in a photographic printer and responsive to exposure data for controlling the duration of an exposure action of a light source (11), comprising an exposure control means (6) characterised by an electronically controlled shutter (41), and characterised in that said exposure control means (6) is adapted for controlling the duration of the exposure action of the electronically controlled shutter (41), and characterised by a converter means (63) responsive to exposure data defining a gray scale, for determining compensated exposure action duration data, with reference to predetermined characteristics of the electronically controlled shutter (41), and in that said exposure controller means (6) controls the duration of the exposure action of the electronically controlled shutter according to the compensated exposure action duration data, wherein the converter means (63) compensates for a non-linear relationship between the duration of application of an exposure voltage and the resultant exposure. An exposure apparatus as claimed in claim 1, wherein the converter means (63) comprises a conversion table in which each item of exposure data refers to a compensated exposure action duration defined by said predetermined characteristics, and means (64) for selecting the data of the compensated exposure action duration by referring to the exposure data in the conversion table. An exposure apparatus as claimed in claim 1 or 2, wherein the converter means (63) comprises a conversion table in which each item of exposure data refers to a compensated exposure action duration defined by said predetermined characteristics, and comprising means (64) for determining a compensated exposure action duration by referring to the exposure data in the conversion table, and combining compensated durations obtained from said table. An exposure apparatus according to any of claims 1 to 3, wherein the converter means (63) comprises a conversion table in which each item of exposure data refers to a compensated exposure action duration defined by said predetermined characteristics, and a compensated exposure light intensity dependent on characteristics of the recording material used and calculated for reproducing a desired color density proportional to the exposure data, and a means (64) for selecting the data of the compensated exposure action duration by referring to the exposure data in the conversion table. An exposure apparatus according to claim 1, wherein the converter means (63) comprises a conversion table in which each item of exposure data refers to a compensated exposure action duration, and an intensity of exposure light proportional to the exposure data, and means (64) for selecting the data of the compensated exposure action duration and the exposure light intensity by referring to the exposure data in the conversion table. An exposure apparatus according to any of claims 1 to 4, further comprising a conversion data setting means (6) for setting, in dependence upon the characteristics of the recording material used, the items of data of the compensated exposure action durations in the conversion table.

Inventors: ISHIKAWA MASAZUMI, KAYAMA YASUTAKA, TANIBATA TOHRU, ISHIKAWA, MASAZUMI, KAYAMA, YASUTAKA, TANIBATA, TOHRU
Applicants: NORITSU KOKI CO LTD, NORITSU KOKI CO., LTD.
Application year: 1995
Main classification: H04N1
IPC codes: G03B27, H04N1