IMAGE READING APPARATUS

Abstract: An image reading apparatus for reading a transparent film comprises a light source, an exchangeable adjusting board corresponding to the transmission factor of the film, imaging means for receiving and imaging the light passing through the adjusting board and the film, comparison means for detecting the output of the imaging means and comparing the output of the imaging means with a predetermined output level, control means for outputting power source control signals according to the output of the comparison means, and a power source for energizing the light source according to the power source control signals, wherein the adjusting board is imaged before the film is imaged by the imaging means, and in case the light amount of the light source is not adequate to the film, the extent of energizing the light source is adjusted so as to be adequate to image the film.

Description: BACKGROUND OF THE INVENTION The present invention relates to an image reading apparatus and more particularly, to an image reading apparatus such as a color copier and a color scanner used to read a transparent film. Conventionally, the same amount of light is irradiated to all the films to be read regardless of the films' transmission factor. So, no consideration is made even when the range of light transmission factor of the films is very wide. This causes inadequacy of white balance adjustment. Especially, when a color positive film with bad light transmission factor is read, the tone of the image required by the reading is far different from that of the original film. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a new image reading apparatus in which the light amount of the light source is adjusted according to the non-uniform and wide range of the transmission factor of the films to be read and the best white balance is provided. Briefly described, in accordance with the present invention, an image reading apparatus for reading a transparent film comprises a light source, an exchangeable adjusting board corresponding to the transmission factor of the film, imaging means for receiving and imaging the light passing through the adjusting board and the film, comparison means for detecting the output of the imaging means and comparing the output of the imaging means with a predetermined output level, control means for outputting power source control signals according to the output of the comparison means, a power source for energizing the light source according to the power source control signals, wherein the adjusting board is imaged before the film is imaged by the imaging means, and, in case the light amount of the light source is not adequate to the film, the extent of energizing the light source is adjusted so as to be adequate to image the film. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention and wherein: FIG. 1 is a block diagram showing the constitution of an image reading apparatus as an embodiment of the present invention; and FIG. 2 is a block diagram showing the electrical constitution of an image reading apparatus as an embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a block diagram showing a constitution of an image reading apparatus as a preferred embodiment of the present invention. A film 11 to be read and imaged is set on the second adjusting board 12b mounted on a transparent board 13. To the left of the second adjusting board 12b in FIG. 1, the first adjusting board 12a is set. The first adjusting board 12a is made preferablly of milk-white resin. There are a plurality of exchangeable boards of various extents of density and the most appropriate one is chosen as the first adjusting board 12a in advance by an operator which has light transmission factor corresponding to that of the film 11. The first adjusting board 12a and the second adjusting board 12b (when 12a and 12b are generically referred, hereinafter shown as 12) are provided for the purpose of diffusing and homogenizing light from a light source 14. The board 13 moves horizontally in the direction of arrows c or d in FIG. 1. Power sources 14R, 14G, and 14B which individually emit red, green and blue light respectively (when 14R, 14G, anf 14B are generically referred, shown as 14) are provided below the board 13. Light from the light source 14 irradiates the film 11 through the board 13. The light source 14 has a length corresponding to the width of the board 13 and is a linear light source, preferably a fluorescent lamp. On the starting of the operation, a first red light source 14R is switched on and the red light passing through the board 13 is diffused and uniformly radiated within the first adjusting board 12a to pass through the left side C of the first adjusting board 12a. At the same time, the board 13 moves in the direction of arrow c (to the left) in FIG. 1 from the point C as a base point. Then the red light from the red light source 14R scans the first adjusting board to its right side D, and after that, scans the film 11 from its left side E to its right side F. After the red light source 14 R reaches the right side F, it is switched off. At the same time, the board 13 moves in the direction of arrow d (to the right) in FIG. 1 back to the base point C. Next, the green light source 14 G is switched on and scans in the same way as the red light source, and at last the blue light source 14B is switched on and scans in the same way, to finalize the scan of the film 11 by all of the light sources 14R, 14G, and 14B. In the scanning, the light from the light source 14 first passes through the first adjusting board 12a and as shown by line m1, reaches a reflection mirror 16. As shown by line m2, it is reflected and passes through the lens 17 to be introduced to an imaging means 18, preferably charge-coupled device (CCD). Then, successively and sequentially, the light passing through the film 11 on the second adjusting board 12b is introduced in the same way as shown by lines m1 and m2. In this way, first, information regarding the white balance from the first adjusting board 12a is introduced to line n1 after converted to corresponding electrical signals, and then, information regarding the color and tone of the film 11 on the second adjusting board 12b is introduced to the line n1 after converted to the corresponding electrical signal. According to the abovementioned electrical signals, controlling is made as described below, and then, the image is processed by an image processing apparatus(not shown in the figures). In the above embodiment, the light from the light source 14 is reflected only once by the reflection mirror 16, but the reflection may not be restricted to be only once, and it may be possible to use several reflection mirrors to lead the light in a desired direction. Also, a lens 17 provided on the optical path may not be restricted to be only at one place. Further, in this embodiment, light source is a linear light source, but surface light source and imaging means for surface-reading may be used to avoid moving the above board 13. FIG. 2 is a block diagram showing an electrical constitution of an image reading apparatus as a preferred embodiment of the present invention. In FIG. 2, for convenience' sake, the board 13 and the lens 17 are omitted and light reflection is made only once by the reflection mirror 16. The output of the imaging means 18 is amplified by an amplifier 19 and is inputted to a comparator 20 as a comparison means used to detect and compare the output of the imaging means 18 with a predetermined level. The comparator 20 compares the input level Vi with the predetermined specified level Vs (for example, Vs = 1V). When Vi < Vs, the comparator 20 outputs logic '0' and when Vi > Vs, it outputs logic '1'. According to the output of the comparator 20, the controlling portion 21 as a controlling means which outputs power controlling signals sequentially inputs pulse controlling signals to the power source 22 which energizes the light source by power source controlling signals so that the light amount of the light source 14 is adjusted. The controlling signals are determined by the abovementioned output level of the comparator 20 '0' or '1'. On starting, the controlling portion 21 gives the controlling signal Pw to the power source 22. Pw is formulated as follows: Pw = T · N ...(1) T is a time function relative to the distance L between the two sides of the first adjusting board 12a (C - D) and to the time required to scan the distance L. N is expressed as a geometrical progression 1/2, 1/4, 1/8, 1/16 . . . when the rated largest light amount of the light source 14 is expressed as 1. At the beginning, N is set as 1/2 and Pw expressed as follows is introduced to the power source 22. Pw = T · (1/2) ...(2) According to this, first, the red light source 14R is energized by the electric power corresponding to 1/2 light amount and is switched on. The light emitted from the light source 14R passes through the first adjusting board 12a and reaches the reflection mirror 16 as shown by line m1, and then is reflected and introduced to the imaging means 18 as shown by line m2. As no film is set of the first adjusting board 12a, all light from the light source 14 R is introduced to the imaging means 18. So, the light amount which is introduced to the imaging means 18 corresponds to the 'white' portion of the film, which means the condition of white balance. If, in this condition, the output level of the comparator 20 is logic '0,' the output level is too low, so the controlling portion 21 increases the level of the controlling signal Pw to the power source 22 so that the following relation is satisfied. Pw = T · { (1/2) + (1/4) } ...(3) If the output level is still '0,' the light amount is still too small, so the controlling portion 21 further increases the level of the controlling signal Pw to the power source 22 so that the following relation is satisfied. Pw = T · { (1/2) + (1/4) + (1/8) } ...(4) If the output level then becomes '1,' for the purpose of fine adjustment of the light amount, 1/16 is subtracted from { } of the right side of the expression (4): Pw = T · { (1/2) + (1/4) + (1/8) - (1/16)}= (13/16) · T ...(5) Namely, the controlling signal Pw corresponding to 13/16 of the rated largest light amount is given to the power source 22. The extent of energizing the light source 14 is thus determined and white balance adjustment is completed. To the contrary, if the first adjusting board have a good transmission factor and, for example, the output level of the comparator 20 is logic '1' at the level (1/2), a quantity between 1/2 and 1/16 is sequentially subtracted until the output level of the comparator 20 becomes logic '0.' For example, if the output level becomes '0' after the subtraction is executed five times: 1/2 - {5 · (1/16)} = 3/16 ...(6) Namely, the controlling signal Pw corresponding to 3/16 of the rated largest light amount is given to the power source 22. The extent of energizing the light source 14 is thus determined and white balance adjustment is completed. The red light source 14R then scans the film 11 on the second adjusting board 12b from its left side E. After reading the red part of the film 11 to the right side F, the red light source 14R is switched off and at the same time, the board not shown in the figures goes in the direction of arrow d (to the right in FIG. 2) back to the base point C, the left side of the first adjusting board 12a. Then, the green light source 14G is switched on. The green light source 14G executes white balance adjustment and scanning of film 11 in the same way as the red light source 14R does. Then, the blue light source 14B is switched on and executes the same action. The reading of the film 11 by the three primary color lights 14R, 14G, and 14B is thus completed. It is an advantage of the present invention that films of wide range of light transmission factor are read with automatic and adequate white balance adjustment, as an appropriate first adjusting board 12a is chosen corresponding to the light transmission factor of the film to be read and white balance adjustment is made by first irradiating the first adjusting board 12a when reading is made. In the abovementioned embodiment, the film to be read is a color positive film, but the present invention can also be applied to a negative film. Further, in the above embodiment, after reading by one color light is completed the board goes back to the base point and as for the next reading by another light, white balance is newly adjusted, but to eliminate the repetition of white balance adjustment regarding the same first adjusting board, white balance adjustment may be done regarding only the first color (for example, red) light. Instead of the first adjusting board 12a, any control, for example, manual keyboard or switch means may be provided for presenting information of the light transmission factor of the film into the control means. While only certain embodiments of the present invention have been described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the present invention as claimed. There are described above novel features which the skilled man will appreciate give rise to advantages. These are each independent aspects of the invention to be covered by the present application, irrespective of whether or not they are included within the scope of the following claims.

Claims: 1. An image reading apparatus for reading a transparent film comprising: light source means; exchangeable adjusting board means corresponding to the transmission factor of said film; imaging means for receiving and imaging the light passing through said adjusting board means and said film; comparison means for detecting the output of said imaging means and compraring the output of said imaging means with a predetermined output level; control means for outputting power source control signals according to the output of said comparison means; and power source means for energizing said light source means according to said power source control signals, wherein said adjusting board is imaged before said film is imaged by said imaging means, and, in case the light amount of said light source is not adequate to said film, the extent of energizing said light source is adjusted so as to be adequate to image said film. 2. The image reading apparatus of claim 1, wherein said exchangeable adjusting board means is chosen among a plurality of boards of various extents of light transmission factor. 3. The image reading apparatus of claim 1 further comprising another adjusting board means on which said film is set. 4. An image reading apparatus for reading a transparent film comprising: light source means for emitting light toward the transparent film; identification means for identifying a specific light transmission factor of the film; control means responsive to information from said identification means for controlling said light source means so as to emit enough radiation to compensate for the light transmission factor of the film. 5. The apparatus of claim 4, wherein said identification means is a board for identifying the specific light transmission factor. 6. An image reading apparatus characterised in that the intensity of a source of illumination utilized in the reading operation is adjustable in accordance with the determined transmissivity of the image carrier.

Inventors: NAGANO, FUMIKAZU
Applicants: SHARP KABUSHIKI KAISHA
Application year: 1987
Main classification: H04N1
IPC codes: H04N1, G06T1, G06K7, G03B27