JP3074115B2 - Image transmission device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image transmitting apparatus for compressing and transmitting image information, and more particularly to an image transmitting apparatus having a scene change detecting function for detecting that a scene has been changed is added to a transmitter. It is about.

[0002]

2. Description of the Related Art When image information is compressed and transmitted, when consecutive frames of images are very similar, predictive coding over two frames, that is, an inter-frame difference for coding a difference from a previous frame. Coding is effective, while predictive coding in the same frame is suitable when the motion of the screen is large. H. CCITT is a video coding standard for videoconferencing and videophone. In the coding system of H.261, a plurality of such coding systems are combined, and switching is performed as appropriate according to the state of an image to perform coding.

[0003]

A so-called scene change phenomenon in which there is no correlation between a certain frame and a previous frame may occur due to scene change or insertion of a different kind of image during image transmission. . In such a case, H.
In the encoding system of the H.261 standard, the mode is automatically set to the INTRA mode (intra-frame correlation mode), and temporarily switches to the encoding transmission state of the entire screen using the quantization value at that time. As a result, the amount of data is significantly increased and the transmission time is prolonged, so that there is a problem that a part of the screen is frozen or many frames are dropped.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an image transmission apparatus capable of reliably detecting the occurrence of a scene change during image transmission and effectively suppressing the amount of dropped frames at this time. .

[0005]

An image transmission apparatus according to the present invention is capable of reliably detecting the occurrence of a scene change by determining whether or not a scene change has occurred based on the rate of change of pixels between frames. is there. That is,
The present invention subtracts the image signal of one frame and the image signal of the immediately preceding frame for each corresponding pixel, and counts the number of pixels having a difference value equal to or more than a certain value in one frame. A feature of the image transmission apparatus is to calculate a change rate and determine whether a scene change has occurred based on the value of the change rate. Further, the present invention stores an image signal of one frame and stores a luminance signal Y, color difference signals C _B and C _R.
Buffer memory 2 for outputting in the order of
And a frame memory 34 for storing the image signal of the previous frame supplied from the buffer memory 2 and subtracting the image signal of one frame inputted from the buffer memory 2 for each pixel corresponding to the image signal of the previous frame read from the frame memory 34 Then, a subtractor 32 for extracting the difference value, a numerical converter 36 for binarizing the value at a predetermined threshold, and counting and storing the number of one of the binarized values Counter 38, a CPU 12 that calculates the rate of change of the image based on the count value read from the counter 38, and converts the numerical value calculated by the CPU 12 into a control signal according to a preset function. And a coding controller 10 for controlling the quantization level of the quantizer.

[0006]

FIG. 1 is a block diagram showing an embodiment of a transmitter side of an image transmission apparatus according to the present invention. In the figure, reference numeral 1 denotes an AD converter for converting an analog video signal supplied from a video camera or the like into a digital image signal. Image signal luminance signal Y outputted from the AD converter 1, the color difference signals C _B, is reduced held in the buffer memory 2 for each C _R.
That is, the number of pixels in the vertical and horizontal directions is 483 × 72.
The original image signal of one frame, which is 0 pixel, is reduced to almost half of 240 × 352 pixels in the buffer memory 2, and the luminance signal Y and the color difference signals C _B , C _R
Are serially rearranged and sent to a pre-filter 4 through an image change rate detector 3 described later. In the pre-filter 4, the image signals are sequentially filtered and supplied to the buffer memory 5.

In the image signal applied to the buffer memory 5, the image data is rearranged for each basic block.
After being sent to the video encoder 6 and subjected to image compression encoding, it is encoded by the transmission encoder 7 into a signal suitable for the transmission path and transmitted from the transmission path. Reference numeral 8 denotes a memory controller that controls image writing and image reading of the buffer memory 2;
Reference numeral 9 denotes a scan converter for controlling scan conversion of the buffer memory 5, and reference numeral 10 denotes an encoding controller for controlling a quantization level in the video encoder 6, both of which are controlled by the CPU 12.

FIG. 2 is a block diagram showing the configuration of the image change rate detector 3 and its surroundings. A portion surrounded by a broken line corresponds to the image change rate detector 3, and reference numerals 2, 10, and 12 denote the aforementioned buffer memory, encoding controller, and CPU, respectively. Reference numeral 34 denotes a frame memory that stores the image signal of the immediately preceding frame. The subtractor 32 converts the n-th one-frame image signal input from the buffer memory 2 into a frame memory.
The image signal of the (n-1) th frame read out from S34 and the corresponding pixel are subtracted to obtain a difference value. R
The numerical value converter 36 composed of an OM or the like binarizes the value of this difference into either “1” or “0” at a predetermined threshold. Then, the number of “1” of the binarization is counted and stored by the counter 38 for each frame. The binarization and counting need only be performed for the luminance signal Y having a large data amount in the image signal.

The CPU 12 reads the count value from the counter 38 and calculates the rate of change of the image to be a percentage of the total number of pixels 352 × 240, for example. The coding controller 10 to which the change rate is input converts the control signal into a control signal corresponding to the change rate according to a preset function, and controls the quantization level Q of the video encoder 6 by the control signal. FIG. 3 shows an example of a function curve of the change rate and the quantization level Q when the area where it is determined that a scene change has occurred is set to 50% or more.

In this case, when the rate of change is 50%, a control signal with a quantization level Q of 8 is used. When the rate of change is 80%, a control signal with a quantization level Q of 16 is used for coding control. Output from the encoder 10 to the video encoder 6. The amount of information generated by encoding in the video encoder 6 changes depending on the value of the quantization level Q. As the quantization level Q increases, the quantization interval increases and the amount of image data generated is suppressed.

In the function curve of FIG. 3, when the rate of change is 50% or more, it is determined that a scene change has occurred, and the amount of generated image data is suppressed. When the rate of change is less than 50%, the encoding controller 10 sets the quantization level Q
Is controlled to be as small as possible. Note that the value of the change rate for determining a scene change is not necessarily set to 50%. What is necessary is just to select a value considered to be optimal according to the type of video, such as 40% or 60%.

By the way, when the rate of change of pixels between successive frames is calculated, for example, 40%, 30%, 40%,
In some cases, large values such as 50%, 50%, 30%, 80%, and 50% continue. In the above method, the change rate is 5
When it is 0% or more, it is determined that a scene change has occurred. In this case, it is determined that four scene changes of 50%, 50%, 80%, and 50% have occurred. Then, every time it is forced into INTRA mode,
Generation of data to be encoded is suppressed. As a result, unnecessarily coarse encoding continues, and deterioration in image quality becomes noticeable. However, even when the values of the large change rate continue, it is often not a scene change in many cases. In the above example, it is considered that the scene change occurs only once when it reaches 80%.

Therefore, as means for determining whether or not a scene change has occurred, a difference value between a plurality of change rates may be used instead of using the change rate of pixels between two consecutive frames. That is, the difference between one change rate and the change rate immediately before is calculated, and its absolute value is, for example, 40%.
At this time, it is determined that a scene change has occurred. Next, an example will be described.

Now, the change rate of pixels between successive frames is 40%, 30%, 40%, 50%, 50%, 30%.
%, 80%, and 50%. For the first 50%, the change rate immediately before is 40%, so the difference between the two changes is 50−40 = 10, and the absolute value of the difference is also 10%.
And it is determined that it is not a scene change. next,
For 80%, the previous change rate is 30%,
The difference between the two change rates is 80−30 = 50, and the absolute value of the difference is 50, which is determined as a scene change.

Further, by using the average value of a plurality of change rates instead of taking only one change rate as the immediately preceding change rate, the accuracy of determination can be further improved. That is, a difference between one change rate and an average value of a plurality of change rates immediately before the change rate is calculated, and when the absolute value is, for example, 30% or more, it is determined that a scene change has occurred. Next, an example will be described. The number of change rates to be averaged may be plural, but three average values are taken here. As in the previous example, the rate of change of pixels between successive frames is 40%, 30%, 40%, 50%, 50%, 3%.
It is assumed that 0%, 80%, and 50% continue.

First, for the first 50%, the average value of the three previous change rates of 40%, 30%, and 40% is about 37%, so the difference between this average value and the current change rate is about 37%. Is 50-37 = 13, the absolute value of the difference is 13, and it is determined that this is not a scene change. In the case of the second 50%, the average value of the immediately preceding three change rates of 30%, 40%, and 50% is 40%, so the difference between this average value and the current change rate is 50-40 = At 10, the absolute value of the difference becomes 10, and it is again determined that the scene change is not made.

Next, for 80%, the average value of the three previous change rates of 50%, 50%, and 30% is about 43%, so the difference between this average value and the current change rate is: 80-4
When 3 = 37, the absolute value of the difference becomes 37, and a scene change is determined. For the third 50%, the average of the three previous rates of change of 50%, 30% and 80% is about 53%. Therefore, the difference between the average value and the current change rate is 50−53 = −3, and the absolute value of the difference is 3, and it is determined that the scene change is not made. The calculation of the difference value between the plurality of change rates and the average value of the plurality of change rates is performed by the CPU 12 of FIG.

FIG. 4 shows another embodiment of the image transmission apparatus according to the present invention. As in FIG. 2, an image change rate detector and its periphery are shown in a block diagram. In this example, in addition to the above configuration, a second numerical converter 42 and an adder 44 are added to provide a noise reduction function. The value of the difference of each pixel of the image signal between the two frames extracted from the subtractor 32 is converted by the numerical value converter into a numerical value according to a preset function. The function at this time is, for example, 0 when the difference is 0, and 0 when the difference is 1.
In addition, it is set so that numerical conversion is performed such that the value is suppressed to a small value, such as 1 when the difference is 2, 2 when the difference is 3, and 3 when the difference is 5. Then, the adder 44 performs an arithmetic process of adding the signal of the pixel corresponding to the image signal of the previous frame to the numerical value converted by the numerical value converter 42, and the operation result is stored in the frame memory 34. As a result, the difference value between the frames becomes smaller,
Image noise will be reduced.

[0019]

According to the present invention, the occurrence of a scene change can be reliably detected, and the occurrence of dropped frames can be effectively prevented. In addition, not only can the main part of the image change rate detector 3 be used for noise reduction, but also the count value of the counter in the image change rate detector 3 can be used for determining the filtering coefficient in the pre-filter 4. A multifunctional image transmission device can be obtained without increasing the size of the circuit device.

[Brief description of the drawings]

FIG. 1 is a block diagram of a transmitter showing an embodiment of an image transmission apparatus according to the present invention.

FIG. 2 is a block diagram of a main part of the image transmission apparatus.

FIG. 3 is a correlation diagram showing one setting example of a relationship between an image change rate and a quantization level.

FIG. 4 is a block diagram of a main part showing a second embodiment of the image transmission apparatus of the present invention.

[Explanation of symbols]

 2 Buffer memory 3 Image change rate detector 6 Video encoder 10 Encoding controller 12 CPU 32 Subtractor 34 Frame memory 36 Numeric converter 38 Counter

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 11/00-11/24 H04N 7/24-7/68 H04N 9/79-9/898 H04N 5 / 91-5/956

Claims (5)

(57) [Claims] 1. A frame determined to have a scene change
When encoding data, reduce the amount of data to be encoded.
In an image transmitting apparatus for compressing and transmitting image information, the image signal of one frame and the image signal of the immediately preceding frame are subtracted for each corresponding pixel, and pixels having a difference value equal to or greater than a certain value are subtracted. An image transmission apparatus characterized in that a change rate is calculated by counting the number of scene changes in one frame, and it is determined whether a scene change has occurred based on the value of the change rate. 2. A luminance signal Y and the chrominance signal C _B, an image transmission apparatus for transmitting an image signal consisting of C _R and compression-encoded by digitized video encoder, the luminance signal stored in the image signal of one frame Y, color difference signal C
_B , C _R , a buffer memory that outputs in the order, a frame memory that stores the image signal of the previous frame supplied from the buffer memory,
The image signal for the frame is subtracted for each pixel corresponding to the image signal of the previous frame read from the frame memory,
A subtractor for extracting the value of the difference, a numerical converter for binarizing the value at a predetermined threshold, and counting the number of one of the binarized values to calculate the counted value. A counter for storing, a CPU for calculating an image change rate based on the count value read from the counter, and a numerical value calculated by the CPU converted into a control signal in accordance with a preset function, and a video code is generated by the control signal. 2. The image transmission apparatus according to claim 1, further comprising: an encoding controller that controls a quantization level of the encoder. 3. The image transmission apparatus according to claim 2, wherein the CPU further calculates an absolute value of a difference between the one change rate and the immediately preceding change rate and outputs the absolute value to the encoding controller. 4. The CPU further calculates an absolute value of a difference between one change rate and an average value of a plurality of change rates immediately before the change rate and outputs the calculated absolute value to the encoding controller.
Image transmission device. 5. A second numerical converter and an adder are added, and a difference value between pixels of an image signal between two frames extracted from the subtracter is converted into a numerical value according to a preset function. 3. The arithmetic processing according to claim 2, wherein the arithmetic processing is performed by adding the signal of the pixel corresponding to the image signal of the previous frame to the numerical value in the adder, and the result of the arithmetic operation is stored in the frame memory. Image transmission device.