AU681565B1

AU681565B1 - Image signal processing apparatus

Info

Publication number: AU681565B1
Application number: AU10140/97A
Authority: AU
Inventors: Cha-Lin Tsai; Dennis Ou Yang
Original assignee: Umax Data System Inc
Current assignee: Veutron Corp
Priority date: 1997-01-13
Filing date: 1997-01-13
Publication date: 1997-08-28
Anticipated expiration: 2017-01-13
Also published as: GB9700579D0; GB2321152A; GB2321152B

Description

S F Ref: 365584

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

L I- 0* Name and Address of Applicant: Umax Data Systems Inc.

No.1-1, R&D Rd.2 Science-Based Industrial Park Hsinchu

TAIWAN

Dennis Ou Yang, Cha-Lin Tsai *r 0 Actual Inventor(s): Address for Service: Invention Title: Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Image Signal Processing Apparatus The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845 -L IMAGE SIGNAL PROCESSING APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal processing system, and particularly to image signal processing apparatus having a multiplexer and a Gamma 10 mapping table using fewer data.

*o o« 0 S 2. Description of the Prior Art *e An image signal processing system electrically generates an image signal 15 through focusing a scanned light beam and using a photodetecting device such as charge-coupled devices (CCDs). The collected image signal is then further processed, S. stored and displayed for some applications. Image scanners, camera recorders and facsimile machines are some examples among the widespread applications of the image signal processing systems in modem offices and home.

A functional block diagram of a conventional image system is shown in FIG. 1.

An, image of a document, which is lightened by a lamp 10 and reflected by a mirror 11, is focused by a lens 12. The focused image is then detected by a CCD 13, followed by being processed via a pre-processing circuit 14 such as a direct current (DC) gain II amplifier. Thereafter, the pre-processed signal is transformed from its analog form to an equivalent digital form by an analog-to-digital converter (ADC) 15, where the reference input to the converter 15 is generated by a digital-to-analog converter (DAC) 16. The digitized signal is further processed by a post-processing circuit 17, such as a Gamma correction, and is then stored in a memory buffer 18 for a further processing or display.

There are some drawbacks associated with above conventional image signal processing system. Firstly, as the number of the system bits in ADC 15 increases, the bits in DAC 16 increase accordingly, thereby slowing down the whole image signal '.10 processing system due to the high internal equivalent impedance in the DAC 16.

I Secondly, for a DAC 16 having more bits, the cost grows and the availability in the market becomes low. Thirdly, adjustment of reference voltage 19 of ADC 15 through DAC 16 largely slows down the ADC 15 due to long settling time of the DAC 16.

Moreover, a fluctuating reference voltage 19 usually results in noise, further 15 destabilizing whole system.

The sub-system including pre-processing circuit 14 through the memory buffer 18 of FIG. 1 is used to process one of three colors, red, green and blue. Two identical sub-systems are further required for processing other two colors, thus wasting lot of circuit area and power consumption.

SUMMARY OF THE INVENTION In accordance with the present invention, image signal processing apparatus having a multiplexer and a Gamma mapping table using fewer data is provided. In one embodiment, a scanning circuit is used to generate color signals for each scanned pixel, and the color signals are then multiplexed. The direct current (DC) level of the multiplexed color signal are adjusted by an adjusting circuit, and the analog form of the adjusted color signal are converted by an analog-to-digital converter to an equivalent digital form. A compensating circuit is used to compensate the digitized color signal for shading effect caused by the other portion of the image signal processing apparatus, and an enhancing circuit is used to enhance portion of the compensated color signal in according to the intensity of the compensated color signal. The enhancing circuit 0 includes a mapping circuit to generate a mapped color signal for each compensated color signal using an interpolation method, where the mapped color signal and the compensated color signal are mapped in according. to a Gamma characteristic. Further, the mapped color signals are stored in. a storage where the number of the mapped color signals is less than the number of the compensated color signal, thereby substantially saving memory area. Finally, the enhanced color signals of each scanned pixel are stored in serial in a memory.

0 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a functional block diagram of a conventional image system.

FIG. 2 shows the block diagram illustrating one embodiment of the present invention.

FIG. 3 shows the timing diagrams illustrating the multiplexing of the present invention.

FIG. 4A shows a Gamma curve having a value less than one.

FIG. 4B shows a Gamma curve having a value greater than one.

FIG. 4C shows an interpolated Gamma curve in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 2 shows the block diagram illustrating one embodiment of the present invention. A reflected and focused image representing the scanned pixel of a picture or a 10 document is detected by an array of charge-coupled devices (CCDs) 20, therefore transforming the intensity of the image to electrical color signals of red, green and blue.

a The color signals are then multiplexed by a multiplexer 22, which allocates red, green and blue color signals into adjacent time slot in serial. The output of the multiplexer 22 is selected by two selection digital signals SO, S1 as shown in FIG. 3, where the signal C is 15 a signal from the CCD 20. The high-voltage portion represents the start point of one scanned pixel. The red color signal passes as S1SO is equal to 0 0, the green color signal

*SSSS.

passes as SlSO is equalto 0 1, and the blue color signal passes as SlSO is equalto 1 0. It is understood that the number of the selection signals can be different to two, and the S" sequence of the color signals can be different to that shown in FIG. 3 without departing from the spirit of the present invention.

An adjusting circuit 24 is used to adjust the direct current (DC) level of the multiplexed color signal to an optimum operating range of an consequently used analogto-digital converter (ADC) 26. In this embodiment, an operational amplifier 240 with some feedback circuit (not shown) is used to generate an amplified signal in accordance with a reference DC voltage 242. The gain of the amplified signal is then adjusted by a gain amplifier 244.

The ADC 26 is conventionally used to convert the analog form of the adjusted color signal to an equivalent digital form. The number of bits of the ADC 26 depends on the accuracy the system requires and the cost expense allowed.

An image scanned by an image system, such as a scanner, stored in a computer, 10 and then reproduced on a paper usually possesses some undesirable lines which are darker or brighter than the adjacent portion of the image, ruining the image as a whole.

In a worse case, a band of those undesirable darker or brighter lines can make the image unrecognizable. The aforementioned line or streak is often referred to as shading in image process terminology. The cause of the shading effect is primarily the image 15 defects or distortion of intensity caused by the photo-response non-uniformity of the light source, the mirror, the lens and the charge-coupled devices(CCDs), the aging of the system and the effect resulted from a dusty environment. The shading effect caused by the other portion of the image signal processing system is thus compensated of corrected by a shading circuit 28. The conventional shading correcting method and circuit is employed to compensate the aforementioned shading effect.

A Gamma circuit 30 is utilized to enhance a portion of the compensated color signal from the shading circuit 28 in according to the intensity of the compensated color signal FIG. 4A shows a characteristic curve having a Gamma value less than one, where brighter input signals near intensity level 1024 are thus enhanced. On the contrary, a characteristic curve having a Gamma value larger than one, shown in FIG. 4B, is used to enhance darker input signals near intensity level 0. Conventionally, the Gamma circuit described above is fimplemented by a mapping method to map every compensated color signal from the shading circuit 28 to an enhanced output signal. As the system bits increase, the mapping data stored in a memory area, also referred to as mapping table, increase beyond the image signal processing system can tolerate. In order to overcome the stated problem, in this embodiment only a portion such as half or one fourth of the mapping data in. the present invention are used. An interpolation method is used to generate a Gamma-corrected signal for an input signal not found in the existent mapping So.

table. FIG. 4C illustrates a general example of the interpolation method, where Xl, X2 an 1,Y are existent input data and the output data. For a non-existent input X, its corresponding output Y is generated according to the following equation: Y (Y2-YI) Yl (1) :15 The equation can be implemented in a conventional hardware method for speeding up system performance. However, if time is not a primary consideration, a conventional software method can be used to implemented the equation Processing such as highlight or shadow can be further performed using a post-processing circuit 32. The highlight or shadow circuit is used primarily to conventionally produce a highlight or shadow effect on the intensity of a portion of the enhanced color signal from the Gamma circuit 30. In addition to the aforementioned highlight or shadow circuit, other traditional post-processing fimctions can also be performed here appropriately.

Finally, the processed color signals are stored in a memory device 34 such as a random access memory (RAM). As the original signals out of the CCD 20 are multiplexed by the multiplexer 22, the processed color signals are required to place in the memory 34 in a serial way such as R1G1B1R2G2B2........, where R1 represents the red color signal of the first pixel, Gl represents the green color signal of the first pixel, etc. However, for the conventional image processing system without a multiplexer, the color signals are instead placed in a way as R1R2R3...RnG1G2G3...GnB1B2B3...Bn.

10 Although specific embodiments have been illustrated and described, it will be obvious to those skilled in the art that various modification may be made without departing from the spirit which is intended to be limited solely by the appended claims.

-I -LLI- I

Claims

1. Image signal processing apparatus, comprising: scanning means for generating a plurality of color signals for each scanned pixel, said color signals being then multiplexed; adjusting means for adjusting the direct current (DC) level of the multiplexed color signal; analog-to-digital converting means for converting the analog form of the adjusted color signal to an equivalent digital form; compensating means for compensating the digitized color signal for shading Si effect caused by the other portion of the image signal processing apparatus; enhancing means for enhancing portion of the compensated color signal in according to the intensity of the compensated color signal; and 15 memory means for storing the enhanced color signals, said enhanced color signals of each scanned pixel being stored in serial in said memory means.

2. The apparatus according to claim 1, wherein said scanning means Scomprises: a plurality of detecting devices for transferring the light intensity of the scanned pixel to said color signals; and multiplexing means for multiplexing said transferred color signals into said adjusting means. ii

3. The apparatus according to claim 2, wherein said detecting device is a charge-coupled device (CCD).

4. The apparatus according to claim 2, wherein said multiplexing means comprises a multiplexer, wherein read, green and blue colors of the color signals being multiplexed in accordance with two control signals to the multiplexer.

The apparatus according to claim 1, wherein said adjusting means comprises: 10 an operational amplifying circuit for inputting the multiplexed color signal and age. a reference signal to generate an amplified signal; and 0 a direct current (DC) gain amplifying circuit for adjusting the direct current S (DC) level of the amplified signal to the operating range of said analog-to-digital converting means.

6. The apparatus according to claim 1, wherein said enhancing means comprises mapping means for generating a mapped color signal for each compensated color signal, said mapped color signal and said compensated color signal being mapped 0* Sin according to a Gamma characteristic.

7. The apparatus according to claim 6, wherein said mapped color signals are stored in storage means, the number of the mapped color signals is less than the number of the compensated color signal, thereby substantially saving memory area.

8. The apparatus according to claim 7, wherein the mapping method of said mapping means is an interpolation method.

9. The apparatus according to claim 1, further comprising post- processing means connected between said enhancing means and said memory means for further processing the enhanced color signal.

The apparatus according to claim 9, wherein said post-processing means comprising highlight processing means for highlighting the intensity of a portion of the enhanced color signal. o* *604:

11. The apparatus according to claim 9, wherein said post-processing means comprising shadow processing means for shadowing the intensity of a portion of the enhanced color signal. i*4

12. Image signal processing apparatus, comprising: scanning means for generating a plurality of color signals for each scanned pixel, said color signals being then multiplexed; adjusting means for adjusting the direct current (DC) level of the multiplexed color signal; analog-to-digital converting means for converting the analog form of the adjusted color signal to an equivalent digital form; compensating means for compensating the digitized color signal for shading effect caused by the other portion of the image signal processing apparatus; I- -I enhancing means for enhancing portion of the compensated color signal in according to the intensity of the compensated color signal, said enhancing means comprises mapping means for generating a mapped color signal for each compensated color signal using an interpolation method, said mapped color signal and said compensated color signal being mapped in according to a Gamma characteristic, said mapped color signals are stored in storage means wherein the number of the mapped color signals is less than the number of the compensated color signal, thereby substantially saving memory area; and memory means for storing the enhanced color signals, said enhanced color 10 signals of each scanned pixel being stored in serial in said memory means. 4*9*.

13. The apparatus according to claim 12, wherein said scanning means comprises: a plurality of detecting devices for transferring the light intensity of the 15 scanned pixel tw said color signals; and multiplexing means for multiplexing said transferred color signals into said *o adjusting means.

14. The apparatus according to claim 13, wherein said detecting device is a charge-coupled device (CCD). The apparatus according to claim 13, wherein said multiplexing means comprises a multiplexer, wherein read, green and blue colors of the color signals being multiplexed in accordance with two control signals to the multiplexer.

I

16. The apparatus according'to claim 12, wherein said adjusting means comprises: an operational amplifying circuit for inputting the multiplexed color signal and a reference signal to generate an amplified signal; and a direct current (DC) gain amplifying circuit for adjusting the direct current (DC) level of the amplified signal to the operating range of said analog-to-digital converting means. 10

17. The apparatus according to claim 12, further comprising post- processing means connected between said enhancing means and said memory means for 0 further processing the enhanced color signal. 0*

18. The apparatus according to claim 17 wherein said post-processing 15 means comprising highlight processing means for highlighting the intensity of a portion of the enhanced color signal.

19. The apparatus according to claim 17, wherein said post-processing S means comprising shadow processing means for shadowing the intensity of a portion of 20 the enhanced color signal. Apparatus substantially as described herein with reference to the accompanying drawings. DATED this THIRTEENTH day of JANUARY 1997 Umax Data Systems Inc. Patent Attorneys for the Applicant SPRUSON FERGUSON 12