WO1992021213A1

WO1992021213A1 - An improved digital video image adjusting circuit and a method therefor

Info

Publication number: WO1992021213A1
Application number: PCT/US1991/003324
Authority: WO
Inventors: Mark C. Hahn
Original assignee: Videonics Incorporated
Priority date: 1991-05-15
Filing date: 1991-05-15
Publication date: 1992-11-26

Abstract

In the present invention, a color adjusting circuit is disclosed. The color adjusting circuit receives a digitized video signal representative of a color component. The digitized video signal (130) is received at a video rate and is compared to a stored digital value (134) which represents the desired value from which the adjustment is to be made. The stored value is compared to the digitized video signal by a comparator (132). In one embodiment, the result of the comparator is a comparison signal indicating a '1' or a '0'. The comparison signal is supplied to a digital switch (238). The switch is activated if the comparison signal is a '1' in which event the switch is switched to a previously stored replacement value. The replacement value is supplied in the data stream and is outputted as part of the adjusted color video signal. If the comparison signal is '0', the original color video signal is outputted as the adjusted color video signal.

Description

AN IMPROVED DIGITAL VIDEO IMAGE ADJUSTING CIRCUIT AND A METHOD THEREFOR

TECHNICAL FIELD

The present invention relates to a method and an apparatus for adjusting a parameter of a video image. More particularly, the present invention relates to a digital circuit for adjusting the color of a video image and a method therefor.

BACKGROUND OF THE INVENTION Video color image adjusting circuits are well known in the art. See, for example, U.S. Patent No. 4,219,841; 4,646,161; 4,797,733; and 4,860,092. Further, adjustment of the color component of a video image by a digital circuit is also well known in the art. See, for example, U.S. Patent No. 4,864,391.

In that patent, however, the digital color adjusting circuit appears to be a masking operation which appears to require complex processing circuits (see especially Fig. 2) . In applications where the color of a video image is desired to be adjusted in "real time," i.e. at a video rate, the complex processing would appear to require expensive components, such as a high speed digital processor.

SUMMARY OF THE INVENTION In the present invention, a digital video signal adjusting circuit is disclosed. The digital video signal adjusting circuit can adjust, for example, the color component of a video signal. The circuit comprises means for receiving the digitized video signal at a video rate to form a received digitized video signal. The digitized video signal is representative of a digitized image. The circuit provides means for storing a first digital value representative of the amplitude of the color component of the desired video signal from which the adjusting circuit would adjust. Means for comparing one value of the received digitized video signal to the stored first digital value to produce a comparison signal is also provided. The one value of the received digitized video signal is replaced by a replacement value in the received digitized video signal in response to the comparison signal to form an adjusted digitized video signal. The adjusted digitized video signal is then outputted.

BRIEF DESCRIPTION OF DRAWINGS Figure 1 is a schematic block diagram of an analog video image color adjusting circuit of the* prior art.

Figure 2 is a schematic block diagram of a digital video image color adjusting circuit of the prior art. Figure 3 is a schematic block level diagram of a video color adjusting circuit including a novel digital video image color adjusting circuit. Figure 4 is a detailed schematic block level diagram of one embodiment of a novel digital video image color adjusting circuit.

Figure 5 is a detailed schematic block level diagram of another embodiment of a novel digital video image color adjusting circuit.

Figure 6 is a detailed schematic block level diagram of yet another embodiment of a novel digital video image color adjusting circuit.

Figure 7 is a graph of the output of the function generator, which is a portion of Figure 6, as a function of the difference value. Figure 8 is a schematic block level diagram of a circuit to input the comparison value used in the novel digital video image color adjusting circuit.

Figure 9 is a detailed schematic diagram of the component of the circuit shown in Figure 8 to store the comparison value.

Figure 10(a-c) is a detailed schematic block level diagram of the preferred embodiment of the present invention to adjust the chroma and the luminance of a color video signal, at a video rate.

DETAILED DESCRIPTION OF THE DRAWINGS Referring to Figure 1 there is shown a block level diagram of an analog color adjusting system 10, employing an analog color adjusting circuit of the prior art. The system 10 comprises a source of video signal 12. The video source 12 can be, for example, the tuner of a television receiver, or the video output of a video recorder. The output of the video source 12 is an analog video signal 14. The analog video signal 14 is representative of a video image and is supplied, at a video rate to a demodulating circuit 16. In the NTSC standard, the video rate is approximately 4.7 MHz.

From the demodulating circuit 16, the color components of the video image, comprising of the color vector signals Y, I, and Q are supplied to a matrix circuit 18. The output of the matrix circuit 18 are the color component signals R, B, and G.

The matrix circuit 18 generates the R, B, and G signals, each of which is typically supplied to a potentiometer 20, with one potentiometer 20 (a-c) to receive each of the color component signals R, B, and G. The output of each of the potentiometers 20a, b, and c, is the adjusted color component signals R, B, and G. The adjusted color component signals R, B, and G are supplied to an inverse matrix circuit 22. From the inverse matrix circuit 22, the adjusted color vector signals Y, I, and Q are supplied to a modulating circuit 24, from which the adjusted analog video signal 26 is produced.

As can be seen from the prior art system 10, the adjustment of the potentiometers 20(a-c) adjusts each of the color component signals from the analog video signal 14.

Referring to Figure 2, there is shown another color video adjusting system 10 of the prior art. The analog video signal 14 is supplied to an analog- to-digital converter circuit 15 which digitizes the analog video signal 14. The digitized video signal is then supplied to a digital demodulating circuit 16 from which the color component signals Y, I, and Q are produced. These signals are then supplied to a digital processing circuit 17, which processes the digitized color component signals Y, I, and Q, and produces the adjusted color component signals Y, I, and Q.

The adjusted color component signals Y, I and Q are supplied to the digital modulating circuit 24. The digital video signal from the modulating circuit 24 is then converted into analog form by the digital- to-analog converter circuit 25. A clock 30 provides the necessary clocking or synchronizing signals to each of the component circuits, such as the demodulating circuit 16, the digital processing circuit 17, and the modulating circuit 24.

Referring to Figure 3 , there is shown a color adjusting system 110 including the color adjusting circuit 120 of the present invention. The color adjusting system 110 comprises a video source 12 which provides an analog video signal 14. The analog video signal 14 is supplied to an analog-to-digital converter 15, from which a digital video signal is produced. The digital video signal is then demodulated by a demodulating circuit 16 which produces the digital color vector signals Y, I, and

Q.

The digital color vector signals Y, I, and Q are then supplied to a digital matrix circuit 18 from which the color component signals R, B, and G are produced. Each of the digitized color component signals R, B, and G is a synchronized digital video sample signal with an amplitude representative of the magnitude of the color component. Each of the R, B, and G signals is supplied to a substantially identical color adjusting circuit 120 of the present invention. From the color adjusting circuit 120, the adjusted digital color signals, R, B, and G are supplied to a digital inverse matrix circuit 122. From the digital inverse matrix circuit 122, the adjusted digital color vector signals Y, I, and Q are supplied to a digital modulating circuit 24. The digital modulated signal is then supplied to a digital-to-analog circuit 25 which produces the color adjusted analog video signal 26. A clock 30 provides the necessary clocking or synchronizing signals to each of the component circuits, such as the demodulating circuit 16, the matrix circuit 18, each of the color adjusting circuits 120, the inverse matrix circuit 122, and the modulating circuit 24.

Referring to Figure 4, there is shown a detailed schematic block level diagram of the color adjusting circuit 120 of the present invention shown in Figure 3. As previously discussed, three of these circuits are provided: one for each o.f the digitized color co ponent signals R, B and G, 130 with all three circuits 120 being substantially identical. Thus, in Figure 4, the circuit 120 is shown for operating on the digitized R or Red color component signal 130. The digitized R color component signal 130 is supplied to the color adjusting circuit 120 at a video rate. The digitized R component color signal 130 is supplied to a comparator 132. A previously stored digital value of the R color, stored in a first storage location 134, is also supplied to the comparator 132. (Hereinafter called the "comparison value". The mechanism of storing the comparison value will be discussed hereinafter.) The digitized R color signal 130 is then compared to the comparison value 134 by the comparator 132.

The digitized R color component signal 130 is also supplied to a switch 138. The switch 138 has two inputs: one is from the R color component signal 130; the other is from a replacement value of R stored in a second location 140 (Hereinafter called the "replacement value") . The result of the switch 138 is the generation of an adjusted R color signal 142. Because the signal 130 is a digitized synchronized signal, the clock signal is also supplied to the comparator 132 and the switch 138.

In the operation of the color adjusting circuit 120, if the current value of the digitized R color component signal 130 equals to the comparison value, the comparator 132 generates the comparison signal 136 of "1". The comparison signal 136 is used to switch the switch 138 such that the replacement value 140 is then supplied to the switch 138. The replacement value 140 is then supplied on to the adjusted digitized color component signal 142. In the event the digitized R color component signal 130 is different from the comparison value, (as, for example, in the pixel after the pixel(s) having the match) , the comparator 132 generates a comparison signal 136 of "0". In that event, the switch 138 is not activated and it remains in the position of supplying the R color component signal 130 as the adjusted color component signal 142.

As can be seen from the foregoing, the method and apparatus of the present invention is the comparison of the color value in the color image signal to a comparison value, and the replacement of the value in the color image signal by a replacement value. Since the method and apparatus of the present invention uses a simple compare and replacement action, the circuit to accomplish that function, can be simplified. Thus, the adjusting circuit 120 does not require extensive digital processing capabilities. Because the method and apparatus of the present invention is a simple comparison and replacement operation, the method and apparatus of the present invention can even "adjust" the color of a video signal by, for example, changing an entire red field to green, without requiring extensive digital processing circuitry. Furthermore, one can even change the color of a single pixel without changing the color of the rest of the field.

Referring to Figure 5, there is shown another embodiment of the color adjusting circuit 220. The color adjusting circuit 220, similar to the color adjusting circuit 120, has a comparator 132. The comparator 132 receives the digitized color video signal 130 at the video rate and receives the comparison value 134 and generates a comparison signal 136 in response thereto. The comparison signal 136 can be a "1" in the event the digitized video signal 130 is the same value as the comparison value or, is the value "0" when the two values are different.

A fractional value "f" can be user entered and adjusted, or can be pre-stored. The fractional value "f" is supplied to a first subtractor 140, to which the value "1" is also supplied. The subtractor 140 supplies the value "1-f" as its output. The value "f" is also supplied to an AND gate 144, to which the comparison signal 136 is also supplied. The comparison signal 136 is also supplied to an inverter 148 and is then supplied to an OR gate 142. The other input of the OR gate 142 is the output of the subtractor 140. The output of the OR gate 142 is the R multiplier signal 152. The output of the AND gate 144 is the Replace multiplier signal 150.

The switch 238 is shown in greater detail and is more than simply a binary switch. The R multiplier signal 152 is supplied to a first multiplier 222a to which the R signal 130 is also supplied. The Replace multiplier signal 150 is supplied to a second multiplier 222b to which the replace value 140 is also supplied, The output of the first and second multipliers 222a and 222b are summed by the ADDER 224 and produces the adjusted R signal 142 as the output. The operation of the color adjusting circuit 220 can be seen by referring to the following truth table: Comparator 132 R Signal 152 Replace 150 1 1-f f

0 1 0

In the event the R signal 130 matches the comparison value 134, the comparator outputs a "1" indicating a match. In that event, a fractional value "1-f" of the R signal 130 is supplied to the ADDER 224, with another fractional value "f" of the replacement value 140 being supplied to the ADDER 224. The result is a "blend" of the current signal and the replacement signal. In the event there is no match between the current signal 130 and the comparison value 134, a "1" is supplied to the first multiplier 222a and a "0" is supplied to the second multiplier 222b. In that event, the output of the ADDER 224 is simply the current R signal 130. Referring to Figure 6 there is shown yet another embodiment of the color adjusting circuit 320 of the present invention. In this embodiment, the circuit 320 comprises a first subtractor 232, which receives the digital video signal, at a video rate. The other input to the first subtractor 232 is the comparison value 134. Unlike the comparator 132 which outputs only a "1" or a "0," the first subtractor 232 outputs the difference in the digital value between the digital video signal 130 and the comparison value 134.

The comparison signal 136 generated thereby is supplied to a function generator 330 (shown in the dotted line and explained in greater detail hereinafter) . From the function generator 330, a fractional signal "f" and a fractional signal "1-f" are supplied to the switch 238 (as discussed in Figure 5) . The switch 238 receives the digital video signal 130 and the replacement value 140. From the switch 238, the adjusted digital video signal 142 is outputted.

The function generator 330 is shown in greater detail in Figure 6. The function generator 330 comprises a second subtractor 240, which receives the comparison signal 136 and an offset value stored in 242. The output of the second subtractor 240 is a difference between the comparison value 136 and the offset value 242 and is supplied to a minimum circuit 244. The minimum circuit 244 produces the difference between the comparison signal 136 and the offset value 242, if the comparison signal 136 is larger than the offset value 242. Otherwise, the minimum circuit produces a "0". The minimum circuit 244 is well known in the art. The output of the subtractor 240 can be a digital word with one bit ("1" or "0") to indicate (+ or -) . Thus, the minimum circuit 244 can be simply an AND gate, with the one bit anded to the rest of the bit field.

The output of the minimum circuit 244 is supplied to a first multiplier 246, to which a scale value 248 is also supplied. The scale value 248 is multiplied by the output of the minimum value 244 and produces a scaled signal 250. The scaled signal 250 is supplied to a maximum value circuit 252. The maximum value circuit 252 serves to limit the output of the scaled signal 250 to a value between "0" and "1". The maximum value circuit 252 is also well known in the- art. Since the scaled signal 250 is a digitized signal an overflow bit can be provided to indicate greater than "1". The overflow bit can be used with combinatorial logic to limit the bit values in the rest of the field. The output of the maximum value circuit 252 is the fractional value "1-f" signal. The fractional value "1-f" is also supplied to a third subtractor 254 from which the fractional value signal "f" is produced. The fractional value signals "f" and "1-f" are supplied to the first and second multipliers 222a and 222b of the switch 238, as shown and as described in Figure 5.

In the embodiment of the color adjusting circuit 320, the user provides the offset value 242 and the scale value 248, and can adjust those values. The result of the adjustment of those values can be seen by referring to Figure 7. The fractional value "1- f" is zero if the comparison signal 136 is less than or equal to the offset value 242. In that event, the adjusted R signal 142 is simply the Replace signal 140 (the fractional value "i-f" supplied to the first multiplier 222a is "0") . If the comparison signal 136 is greater than the offset value 242, the difference is multiplied by the scale value 248. The scaled signal 250 will have a slope equal to the scaled value 248. The maximum for the scaled signal 250 is limited by the maximum circuit 252, which is "1". In that event, the adjusted R signal 142 is the R signal 130.

The advantage of the function generator 330 is that the adjusting circuit 320 can replace values of the digital video signal that are identical to the comparison value 134 or that are proximately close to that value. Thus, the function generator 330 can vary or adjust the threshold of the comparison to the comparison value 134 to replace it with a "blend" of the replaced value 140 and the current signal 130, until the "blend" is all of the replace value 140. As can be seen by the foregoing, the color adjusting circuits of the present invention 120, 220, and 320 all share the basic inventive feature of comparing a digital video signal, at a video rate, to a comparison value and replacing that value with a replacement value or a function thereof, and outputting an adjusted digital video signal. Thus, the processing circuit required to accomplish the adjusting circuit is greatly reduced. Further, the adjusting circuit of the present invention can be used to adjust parameters other than color, such as grey scale threshold etc.

As previously discussed, the comparison value 134 must be previously stored. This can be accomplished in many different ways. One way is simply for the user to enter the comparison value 134. The user, of course, has to also supply the replacement value 140.

A second method of storing the comparison value, which greatly eases the entering of the data, is shown in Figures 8 and 9. In Figure 8, the image represented by the analog video signal 14 can be displayed on a display, such as a CRT 150. The user is provided with a first and second adjustment knobs 160 and 162, each of which is connected to a potentiometer. The adjustment knobs 160 and 162 adjust two mutually orthogonal and intersecting cursor bars, as shown in Figure 8. At the intersection of the X and Y cursor bars is the desired location.

Referring to Figure 9 there is shown in greater detail a circuit diagram of the capture circuit 170 used to capture the value of the digital video sample 130 to stored it in register 134. The output of the Y potentiometer 162 is supplied to an analog-to-digital (A/D) converter 180, which outputs 8 bits. A line counter register 182 is also provided. The input to the line counter 182 is the Horizontal Line Clock signal (which increments upon the detection of each occurrence of a horizontal sync signal) . The line counter 182 is reset by the detection of a vertical sync signal. Thus the line counter 182 stores a count of the number of horizontal lines. The output of the line counter 182 is supplied to a comparator 184, to which the output of the A/D 182 is also supplied. The output of the comparator 184 is supplied to an OR gate 186 and an AND gate 188.

The output of the X potentiometer 160 is supplied to an A/D converter 190, which outputs 10 bits. A pixel counter 192 is also provided. The input to the pixel counter 192 is the Pixel Clock signal (which increments upon the detection of each occurrence of a pixel clock signal) . The pixel counter 192 is reset by the detection of a horizontal sync signal. Thus the pixel counter 192 stores a count of the number of pixels in each horizontal line. The output of the pixel counter 192 is supplied to a comparator 194, to which the output of the A/D converter 190 is also supplied. The output of the comparator 194 is supplied to the OR gate 186 and the AND gate 188.

The output of the OR gate 186 is supplied to the graphics generator to generate the cursor bars for display. The output of the AND gate 188 is used to clock in the digital video sample signal 130 into the store register 134.

In the operation of the capture circuit 170, If the desired position, as indicated by the Y potentiometer 162 is not equal to the line counter 182, the output of the comparator 184 is "0". Thus, no display occurs in the Y direction. In the event the Y position, as indicated by the potentiometer 162 is equal to the line counter 182, then the comparator 184 generates a "1", which causes the display signal to go high. The pixel at that location would be "illuminated".

Similarly, If the desired position, as indicated by the X potentiometer 160 is not equal to the pixel 192, the output of the comparator 194 is "0". Thus, no display occurs in the X direction. In the event the X position, as indicated by the potentiometer 160 is equal to the pixel counter 192, then the comparator 194 generates a "1", which causes the display signal to go high. The pixel at that location would be "illuminated".

When the comparator 184 and 194 both go high indicating a match in the X and Y directions, the output of the AND gate 188 is high, which loads the digital video sample value into the register 134^'.

As previously stated, the method and apparatus of the present invention can be used to adjust video parameters other than color. Referring to Figure 10(a-c) , there is shown a preferred embodiment for adjusting the chroma and luminance of a video signal. A source of video signal 12 generates an analog video signal 14. The analog video signal 14 is supplied to a chroma/luma separator circuit 19, which is simply a filter and is well know in the art. Each of the outputs of the chroma/luma separator circuit

19 is digitized by an A/D converter 15 to produce the digitized luma signal Y and the digitized chroma signal C, which contains the color component signals (I and ) . Of course the digitizing of the chroma and luma signals can be done before they have been separated by the separation circuit 19. The adjustment for the chroma and luma signals follow generally the circuit described and shown in Figure 6. The luma signal Y is supplied to a subtractor

322 to which a previously stored comparison luma signal 134Y is also supplied. The output of the subtractor 322 is supplied to an absolute value circuit 324. The output of the absolute value circuit 324 is supplied to a function generator 330, shown and as described in Figure 6. The •f" fractional output of the function generator 330 is supplied to a multiplier 332 to which a constant Yweight is also supplied. , The two are multiplied together and supplied to an ADDER 340.

The chroma signal C is processed in generally the same manner as the luma signal Y. However, because the Chroma signal is synchronized with the color burst portion of the video signal 14, there are four vector components of the chroma signal C which need to be adjusted. These are referred to as Φ**, Φ₂, Φ₃, and Φ₄. The chroma signal C is supplied to a switch 342 which stores the four vector component signals in storage 344a, 344b, 344c, and 344d, respectively. Each of those stored values is supplied to a subtractor 346a, 346b, 346c, and 346d, to which the comparison values of 134C*-, 134C₂, 134C₃, and 134C₄ are respectively supplied. The output of each of the subtractors 346 is supplied to an absolute value circuit 348(a-d). The outputs of the absolute value circuits 348(a-d) are summed by an ADDER 350 and is then supplied to a function generator 330. The "f" fractional output of the function generator 330 is supplied to a multiplier 352 to which a constant Cweight is also supplied. , The two are multiplied together and supplied to the ADDER 340.

From the ADDER 340, the signal is supplied to a maximum circuit 354, which produces the fractional value "f". The fractional value "f" is also supplied to a subtractor, which produces the signal "1-f". The values "f" and "1-f" are supplied to the switches 238 (shown in Figure 10c) . The output of the switches 238 are the adjusted luma signal Y and the adjusted chroma signal C, and each is supplied to a D/A converter 362. The analog luma signal Y and chroma signal C are supplied to the chroma/luma signal combiner circuit 360, which can be simply an adder, to produce the adjusted video signal 364.

In comparison to the color adjusting circuits of the prior art, the advantages of the method and the apparatus of the present invention become readily apparent with its ease simplicity and ease of utility.

Claims

WHAT IS CLAIMED IS:

1. A digital video signal adjusting circuit comprising: means for receiving a digitized video signal at a video rate, representative of a digitized image, wherein said digitized video signal is characterized by a plurality of synchronized values; means for storing a first digital value representative of the desired video signal from which said adjusting circuit would adjust; means for comparing one value from said plurality of synchronized values in said received digitized video signal, to said stored first digital value to produce a comparison signal; means for replacing said one value by a replacement value in said digitized video signal in response to said comparison signal, to form an adjusted digitized video signal; and means for outputting said adjusted digitized video signal.

2. The circuit of Claim 1 further comprising: means for storing a second digital value representative of the desired video signal to which said adjusting circuit would adjust.

3. The circuit of Claim 2 wherein said replacement value is a function of the second digital value and said one value.

4. The circuit of Claim 3 wherein said replacement value is said second digital value.

5. The circuit of Claim 1 further comprising: means for indicating the desired location in the digitized image to which said adjusting circuit would adjust.

6. The circuit of Claim 5 wherein said stored first digital value is the value at said desired location.

7. The circuit of Claim 1 further comprising: clocking means for clocking said digitized video signal into said circuit and for clocking said adjusted digitized video signal therefrom.

8. In a video image color adjusting circuit having means for receiving an analog video signal at a video rate, representative of a color image, means for separating said video signal into a plurality of color component signals, and means for digitizing each of said plurality of color component signals to form a plurality of digitized color video signals, wherein said--improvement comprising: a plurality of substantially like color adjusting circuits, each of said circuits for operating on a different one of said plurality of color video signals, each of said color adjusting circuits comprising: means for receiving one of said digitized color video signals; means for storing a first digital value representative of the desired color video signal from which said adjusting circuit would adjust; means for comparing one value of said received one of said digitized color video signals to said stored first digital value to produce a comparison signal; and means for replacing said one value by a replacement value in said digitized color video signal in response to said comparison signal, to form an adjusted digitized color video signal.

9. The circuit of Claim 8. further comprising means for storing a second digital value representative of the desired color video signal to which said adjusting circuit would adjust.

10. The circuit of Claim 9 wherein said replacement value is a function of the second digital value and said one value.

11. The circuit of Claim 10 wherein said replacement value is said second digital value.

12. The circuit of Claim 8 further comprising: means for indicating the desired location on the color image to which said adjusting circuit would adjust.

13. The circuit of Claim 12 wherein said stored first digital values are the values at said desired location.

14. The circuit of Claim 8 further comprising: clocking means for clocking said digitized color video signals into each of said plurality of adjusting circuits and for clocking said adjusted digitized color video signals therefrom.

15. A method of adjusting the color of an analog video signal, at a video rate, representative of a color image, wherein said video signal is separated into a plurality of color component signals, with each of the color component signals digitized to produce a plurality of digitized color video signals; wherein the improvement comprising: receiving one of said digitized color video signals; storing a first digital value representative of the desired color video signal from which said method of adjusting would adjust; comparing one value of said received one of said digitized color video signals to said stored first digital value to produce a comparison signal; replacing said one value by a replacement value in said one digitized color video signal in response to said comparison signal to form an adjusted digitized color video signal; and outputting said adjusted digital color video signal.

16. The method of Claim 15 further comprising the step of: storing a second digital value representative of the desired color video signal to which said method would adjust.

17. The method of Claim 16 wherein said replacement value in said replacing step is a function of the second digital value and said one value.

18. The method of Claim 17 wherein said replacement value is said second digital value.

19. The method of Claim 15 further comprising: indicating the desired location on the color image to which the method would operate; and storing the values at said desired location as the first digital values.

20. A method of adjusting a digitized video sample signal, representative of a digitized image, comprising the steps of: receiving said digitized video sample signal, at a video rate; storing a first digital value representative of the desired video signal from which said method of adjusting would adjust; comparing one value of said received digitized video sample signal to said stored first digital value to produce a comparison signal; replacing said one value by a replacement value in said received digital video signal, in response to said comparison signal, to form an adjusted digitized video signal; and outputting said adjusted digitized video signal.

21. The method of Claim 20 further comprising the step of: storing a second digital value representative of the desired video signal to which said method would adjust.

22. The method of Claim 21 wherein said replacement value in said replacing step is a function of the second digital value and said one value.

23. The method of Claim 22 wherein said replacement value is said second digital value.

24. The method of Claim 20 further comprising: indicating the desired location on the image to which the method would operate; and storing the values at said desired location as the first digital values.