GB2326043A - Determining the quality of video communications - Google Patents

Abstract

A test suite of objects for providing a series of images communicated between terminals of a video communication system includes a first image (36, 38, 40) for determining the transmitted frames of the video image, a second image (42, 44, 46, 48) for determining the resolution of the video image, and a third image for determining the effect of motion on the frame rate and resolution. A video communication benchmark value is determined based on a viewer's measurements of the received images.

Description

IMPROVEMENTS IN OR RELATING TO VIDEO COMMUNICATIONS.

FIELD OF THE INVENTION The present invention relates generally to the field of video communications, and more particularly to a method and apparatus for providing an objective measurement of the quality of a video image generated from received video data using a video communication system.

BACKGROUND OF THE INVENTION Recently, the use of video communication systems has become more prevalent. This can be attributed to developments in communication technology, and particularly in techniques to fully utilise the available bandwidth of the transmission medium.

Early video communication systems generated a poor quality video images providing small display areas, jerky motion, blurriness, blocky looking artefacts and in many instances the audio failed to synchronise with the video images.

Various national and international bodies have defined standards for the operation of video communication systems. One such standard is the H.320 video conferencing standard issued by the International Telecommunications Union (ITU).

However, the ITU H.320 and other standards have generally only attempted to ensure the compatibility of video conferencing systems from different manufacturers. To date none of the standards bodies has issued standards defining the quality of video communication or of the quality of the video image perceived by the user.

The fundamental objective of recent developments in video communication systems has been to provide the best quality video image within the available data rate. Typically, video data is compressed prior to transmission and decompressed prior to generating an image following transmission.

The ITU H.320 standard supports a wide range of transmission data rates. Sophisticated, video communication systems provide greater levels of data to a single frame of the video image, generating an image having greater resolution. Commonly, the data rates used by video communication systems are 128K bits per second (known as baseband ISDN) and 384K bits per second (known as triple baseband ISDN).

It should be noted that the audio component and the synchronisation component of the generated signal must be subtracted from these data rates. The most commonly used audio compression standard is the ITU G.728 standard that requires 16K bits per second.

Since the bandwidth is dictated by the available transmission medium, video communication systems requiring higher data rates generally require greater compression of the video image.

Conventional compression rates for video compression systems are in the range of 100-to-1 to 300-to-1. However, high compression of the video image will invariably result in a loss in the quality of the video image, particularly in sequences with significant changes from frame to frame.

Additionally, the quality of the video image perceived by the user is highly subjective. Each user will attribute different comfort factors to image qualities such as resolution, smooth motion and the synchronisation of audio and video.

SUMMARY OF THE INVENTION Accordingly, the present invention provides a method and apparatus for defining the quality of a received video image generated in a video communication system. As previously stated herein, the quality of the video image perceived will vary according to the personal preferences of the user. Therefore, an objective measurement of the quality of the video image is only possible by simulating a typical application of the video communication system to determine user noticeable effects.

The video communication system is required to compress real-time video and audio data. Depending upon the processing power of the video codec the content of each frame of video data can introduce undesired effects such as dropping of video frames, increased number of artefacts or loss of resolution.

According to a first aspect of the present invention there is provided a method for defining the quality of the received video image generated in a video communication system, which method comprising providing a first video image for determining the frame rate of the video image generated by the video communication system, providing a second video image for determining the resolution of the video image generated by the video communications system, and providing a third video image for determining the effect of motion on the frame rate and resolution of the video image generated by the video communication system.

The video test suite for defining the quality of the video image is intended to simulate a typical application of the video communication system. Since semi-objective measurements of the quality of the video image perceived by the user are required, each of the elements of the test suite are well defined and capable of substantial repetition. Each of the elements of the test suite is further intended to comprise a number of components for assisting the user in determining the quality of the perceived video image without imposing personal impressions on the resulting quality measurement.

Therefore, the video test suite comprises elements for providing an indication of the frame rate of the video image, to assist in determining the resolution of the video image, and for simulating motion on the video image.

According to a second aspect of the present invention there is provided a method for determining the synchronisation between the audio and video components of the received video signal.

BRIEF DESCRIPTION OF THE DRAWINGS These and other features of the present invention will be described in the following detailed description of preferred embodiments of the inventions, by way of example, with reference to the accompanying drawings in which: Figure 1 shows a schematic block diagram of a conventional high specification video communication system; Figure 2 shows a block schematic illustration of apparatus for use in accordance with the invention; Figure 3a is an illustration of a preferred object for use in the determination of video frame rate in accordance with the invention; Figure 3b is an illustration of a preferred object for use in the determination of the resolution of the video image in accordance with the invention; Figure 3c is an illustration of a preferred object for use in the determination of the effect of motion on the resolution and frame rate of the video image in accordance with the invention; and Figure 4 is an illustration of apparatus for use in the determination of synchronisation between the video and audio components of the video image.

For convenience corresponding reference numerals will be used for identifying like and corresponding features of each of the figures of the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS As previously described herein3 resolution is lost from the generated video image due to the compression of the video data for transmission and its subsequent decompression. Video communication systems having greater processing power are more capable of implementing the ITU H.320 standard to produce greater quality video images.

Video communication systems using devices such as the TMS320C80 Multimedia Video Processor produced by Texas Instruments Inc.

utilise a codec (coder/decoder) having H.320/MPEG-1/YPEG functionality for producing high quality video images. However, with so many variables the quality of the video image generated by the video communication systems can differ greatly. To provide the optimal quality of video image, a video communication system must provide an implementation of the ITU H.320 standard that is capable of determining bit allocation decisions to obtain the best quality video image within the available data rate and bandwidth.

The ITU H.320 standard is capable of supporting a range of compression techniques. Different compression techniques may be implemented to compress different portions of a single video frame according to the content of the video image. For example, a first compression technique may be used for compressing portions of the video data containing a background image that remains substantially constant from frame-to-frame, and a second compression technique may be used for compressing portions of the video data that comprise changes in the foreground image from frame-to-frame as may occur with a user waving his hand or nodding his head.

Furthermore, the operating characteristics of the individual video communication system may effect the quality of the video image perceived by the user. These operating characteristics may make a particular video communication system inherently suitable for certain applications, while unsuitable for other applications.

Figure 1 shows a schematic block illustration of a typical highspecification video communication system 10. For convenience, the video communication system 10 will be described in terms of a transmitting portion 11' and a receiving portion 11''.

However, it will be understood by the skilled person that generally operation of the video communication will require both the portion 11' and the portion 11'' to be capable of both generating and transmitting video data, and receiving and converting the video data to generate a video image.

The transmitting portion 11' includes a video camera 12', quantization module 14', coding module 15', pre-processing module 16', loop filtering circuit 17', motion estimation module 18', memory 19', and compression module 20'. Similarly, the receiving portion comprises a video display 12'', quantization module 14'', coding module 15'', post-processing module 16'', loop filtering circuit 17'', motion estimation module 18'', memory 19'', and decompression module 20''. It should be understood that various components described may perform dual functions dependant upon the portion 11' or the portion 11'' operating in a transmitting or receiving mode. It should further be understood that the transmitting portion 11' and the receiving portion 11'' are connected by a transmission medium 21, that may comprise a "hard-wired electrical connection, a fibre optic connection, a radio frequency or a conductive connection.

The video camera 12' of the transmitting portion 11' is connected to the quantization module 14'. The quantization module 14' is capable of assigning each bit of the video data received from the video camera 12' to a predetermined quantization level (N.B. each bit of the video data generally corresponds to a pixel of the image monitored by the video camera 12'). The quantization module 14' is further connected to coding module 15' which receives the quantized video data encodes each 16x16 pixel block in a frame using either an "interframe" or an "intraframe" coding technique. The "interframe" coding technique relies upon error terms used for correction of prediction data contained in a previous reference frame of the video image. Conversely, the "intraframen coding technique relies upon actual pixel data. Selection of the appropriate coding technique will provide a greater quality video image, but use of the "interframe" coding technique is generally limited to video communication systems of greater complexity.

A significant proportion of the compression and data rate control provided by video communication systems operating in accordance with the ITU H.320 standard is provided during the quantization process. As the quantization level rises, fewer bits are required to specify each frequency component of frames of the video image, and smaller valued components may be excised altogether. However, this reduction in the bits required for defining the frames of the video image may result in artefacts and a loss of resolution of the video image. The majority of video communication systems employ a fixed quantization level that is based upon the line rate of the video camera. However, more complex video communication systems employ a solution that dynamically adapts the quantization level according to the content of the video image.

The pre-processing module 16' receives the encoded video data from the coding module 15' and eliminates the randomly generated noise that may cause single pixel errors originating from the video camera 12'. Subsequent compression of this noise will increase the data transmission requirements of the system and waste data bandwidth of the transmission medium. Although simple low pass filtering can reduce the noise, it generally results in blurring of the resulting video image. Therefore, more complex filtering techniques are used (linear or non-linear filtering) in order that the noise generated by the video camera 12' is reduced, while preserving the resolution of the resulting video image.

The compression module 20' receives the encoded and preprocessed video data and performs a compression process on the video data. The compressed video data is then transmitted via the transmission medium 21 to the receiving module 11'', but is also stored in memory 19' to assist with reducing the data content of subsequently transmitted frames of the video image.

At lower bandwidths and with sequences of frames of the video image that are not effectively compressed (i.e. those involving substantial motion), a reduction of the frame rate generally improves the quality of the video image. At relatively low data rates, as may be necessary due to the available bandwidth of standard transmission media, a frame rate that is too high will result in too few bits of the video image being provided to generate an adequate video image. Typically, video communication systems operating in accordance with the H.320 standard will provide a 128K data. rate to produce between 7 and 15 frames per second. However, a lower frame rate may be required during sequences when there is substantial motion between subsequent frames of the video image.

In typical operational situations, the background and various features monitored by the video camera 12' remain substantially stationary from one frame period of the video image to the next frame period. However, movement of a feature between subsequent frame periods will cause pixels reproducing that feature to move as a block.

The encoded video data stored in memory 19' is used by motion estimation module 18'' to generate motion vectors that estimate the position of the each pixel or block of pixels according to the position of that pixel or block of pixels in a preceding frame. Since motion between subsequent frame periods may be relatively complex (e.g. a rotating hand), motion vectors are only capable of providing rough approximations of the position of a pixel or block of pixels. Although additional data can be provided to improve the approximation of the position of the pixel(s), the provision of more accurate approximations of the position of the pixel(s) requires the transmission of less correcting data.

The methods for computing motion vectors vary widely between video communication systems since the ITU H.320 standard does not specify how these motion vectors should be obtained. Video communication systems providing limited motion estimation may comply with the H.320 standard, but will typically provide a relatively poor quality video image. In more complex video communication systems utilising devices such as the TMS320C80, effective motion estimation is achieved through software implemented intelligent algorithms.

Following the generation of motion vectors by motion estimation module 18', a further improvement in the quality of the video image is obtained by reducing large errors in the prediction data and estimation vectors. This is achieved by loop filtering module 17' that performs a loop filtering process when using "intraframe" coding techniques.

Referring now to the receiving portion 11'', compressed and encoded video data is received from the transmitting portion 11' via the transmission medium. The received video data is decompressed at decompression module 20''. However, the compression algorithms implemented by video communication systems may generate "mosquito noise" in the video data that causes artefacts in the resulting video image. Mosquito noise can be attributed to excessive quantization of the video data resulting in the elimination of important high frequency information along contours in the video image (e.g. the edge between a face and the background). Post-processing module 16" provides a reduction in the effects of "mosquito noise" by postprocessing of the video data prior to the display of the video image.

Following post-processing the video data is passed via coding module 15'' and quantization module 14'' to video display 12'' for generation of the video image.

It is preferred that motion estimation and loop filtering be performed by the transmitting module 11'' in order that unnecessary bits of data do not utilise bandwidth that may be more effectively utilised by bits of data that change from frame-to-frame. However, motion estimation can also be performed at the receiving portion 11''.

Furthermore, delays in the transmission of video data and in the generation of the video image result from the need to compress and decompress the video data, together with any inherent delays introduced by the transmission medium. Typically therefore, audio data is delayed in order that it may be synchronised with the video data. Rowever, where a reduction in the data rate results in fewer frames of the video image being provided in a defined time period, as may occur where substantial motion occurs between subsequent frames of the video image, a loss of synchronisation may occur between the audio and video data.

Therefore, the comfort factor for the user of the video communication system is greater where the delay due to compression of the video data is reduced.

Each of the previously described factors, and additional factors not detailed herein but recognisable to the skilled person, contribute to the quality of the video image perceived by the user of the video communication system. However, it should be understood that although the present invention is described in terms of a video communication system complying with the ITU H.320 standard, the present invention is not limited to systems of the H.320 standard or to factors not specifically detailed herein.

Referring now to Figure 2, an apparatus arranged in accordance with the invention is illustrated. An object 30 is monitored by the video camera 12' of the transmitting portion 11' of the video communication system 10. Video data corresponding to the image monitored by the video camera 12' is encoded and transmitted as described with reference to Figure 1. The received video image is then displayed by the video display 12'' of receiving portion 11'' of the video communication system and observed by the user 35. The user 35 assigns a frame rate value, a video communications benchmark (VCB) value, resolution value, motion impact value, synchronisation value, and a weighting value in accordance with the video image perceived by the user 35 of the object 30.

Referring now to Figure 3, the test suite of the present invention provides an object for indicating the frame rate of operation of the video communication system as illustrated by Figure 3a, an object to assist in detecting the resolution of the image generated by the video communication system as illustrated by Figure 3b, and a simulation of motion of an object monitored by the video camera 12' as illustrated in Figure 3c. The present invention utilises the video communication system 10 illustrated in Figure 1 in operation to provide an objective measurement of the quality of the resulting video image.

The object for providing an indication of the frame rate of the video communication system includes two annularly arranged rings of light emitting diodes (LED's). The first (outer) ring comprises thirty LED's, and the second ring comprises twentyfive LED's. The rings of LED's are representative of the numbers of frames necessary to produce a one-second sequence according to the NTSC and PAL transmission standards respectively. Differing numbers of LED's can be provided to represent further transmission standards.

The ring of LED's illustrated in Figure 3a is monitored by the video camera 12'. The LED's are illuminated sequentially in accordance with the frame period of the television transmission standard of the video communication system currently under test.

For example, if a video communication system operating in accordance with the NTSC standard is being tested, the period between the illumination of adjacent LED's will be 1/30 the of a second. Consequently, a one-second sequence of frames will comprise the sequential illumination of each of the thirty LED's of the outer ring of LED's illustrated in Figure 3a.

Observation of the video image generated and displayed on the video display 12'' of a video communication system 10 as illustrated in Figure 1,allows the user thereof to count the number of LED's illuminated. From the video image the user can note LED's that are not illuminated in sequence, and therefore indicative of "dropped" frames. Observation by the user of the video display 12'' in order to determine which frames are dropped in a sequence for a frame will comprise the user noting the sequence of led illumination (i.e. a sequence of YNYNYN where Y is an illuminated frame and N is an un-illuminated frame).

Each test will produce a frame rate value (i.e. the number of frames illuminated in a 1 second period). According to the present invention a visual communication benchmark (VCB) value will be assigned to the system based upon the number of LED's illuminated, and hence the number of frames of video data received, in a 1 second period.

If the frames are not in a continuous sequence or frame dropping is not smooth, the invention reserves a further value to be subtracted from the VCB value in order to define this degradation.

Referring now to Figure 3b, a pseudo-objective method is provided for determining the resolution of the video image due to block artefacts since no objective method is possible. The method of the present invention assumes that one or more users will observe the video image generated by a sequence of annular light and dark regions and assign a resolution value.

The series of annular light and dark regions are designed to assist the user in determining the quality of the perceived video image, while decreasing the subjective impact of the user.

In the illustrated example, the object for providing resolution detection comprises a series of light and dark regions that decrease in size. Generally, a number of such objects will be provided and the resolution value assigned by the user will relate to the object that user considers to comprise least distortion of the video image.

Preferably, the light or dark regions comprise a series of increasingly larger rings (42,44,46,48). Preferably, the breadth of the light or dark regions increases as each ring increases in diameter, and the breadth of the light or dark region may be proportional to the diameter of the ring (42,44,46,48).

Referring now to Figure 3c, motion of the object 35 is performed according to a defined movements. Typically, the motion of the object will be caused by an electrical motor driving a cam under an edge of the object 35. A "real-world" simulation of the object 35 is performed in order that the effects of limited motion, average motion, and extreme motion on the frame rate and resolution of the perceived video image can be determined.

Furthermore, the simulation of the motion of the object 35 will cause block artefacts resulting from the coding algorithms that can assist the user 35 in determining the stabilisation time for the picture. Once motion of the object 35 is ceased, and the image of the object 35 captured by the video camera 12' is stationary, the resolution of the image should increase and the number of block artefacts decrease.

Although not previously described in detail, the video data transmitted between the transmitting portion 11' and the receiving portion 11'' will typically comprise an audio component. The present invention assumes that video communication systems provide a reasonable audio quality.

However, an audio value can be subtracted from the VCB value for poor audio quality as may occur with breaks in audio transmission.

Figure 4, illustrates an apparatus for determining the synchronisation between the audio and video components of the video data.

The following three equations determine the synchronisation between the audio and video component of the generated audio and the displayed video image; ta-a = t im esource~audio-dest~audio (i) tv-v = ti m esource~video-dest~video (ii) tav = t imesource~audio-dest~video (iii) where taa represents the time delay between the generation of the audio data at the transmitting portion 11' and the playing of the audio data at the receiving portion 11'', tV-v represents the time delay between the generation of the video data at the transmitting portion 11' and the display of the video data at the receiving portion 11'', and taV represents the audio-video synchronisation parameter.

The invention will be described further by means of the application of the method of the invention to a practical example of the operational characteristics of a video communication system as described in reference to Figures 1 and 2 herein. For convenience, the method of the invention will be described in terms of its application to a video communication system operating according to the PAL transmission standard.

As previously described herein in reference to Figure 3a, the frame rate (or refresh) rate of the display video image is monitored by the user observing the sequential illumination of LED's 40 in the ring corresponding to the PAL standard (i.e. the inner ring 38). During the monitoring period, of for example, one second, the number of illuminated LED's in the display video image is counted by the user. A value is then assigned according to the number of illuminated LED's observed in the display video image according to Table 1A;

PraM rate (PAL) frames per sec frame rate value 25 100 > 20 95 > 17 90 > 15 80 > 12 60 > 10 40 > 7 20 > 5 10 > 0 0 Table 1 For example, if 19 illuminated LED's 40 are observed in the display video image a frame rate value of 90 is assigned.

Next, the user will observe from the display video image if any frames have been "dropped" during the monitoring period. The user will assign a value according to the number of LED's observed in the display video image that are not illuminated in sequence. For, example a "dropped" frame will have occurred where a non-illuminated frame is observed between illuminated frames in the series of LED's in the ring 38. The value is assigned in accordance with Table 2;

Frame dropping order dropped frames frame dropping value between displayed frames only one dropped 0 frame 2 dropped frames -7 3 dropped frames -15 4 dropped frames -22 5 dropped frames -30 Table 2 For example, if 2 frames are "dropped" during the monitoring period as indicated by two non-illuminated LED's in the sequence of the display video image a frame dropping value of -7 is assigned.

Next, as has previously been described herein with reference to Figure 3b, a value is assigned to the video communication system in accordance with the preferred resolution of the display video image. The user will assign a value corresponding to the preferred one of the series of light and dark regions (42,44,46,48) observed in the display video image. Furthermore, the user will assign the value according to the number of light and dark regions that he can observe in the display video image corresponding to the preferred series of light and dark regions (42,44,46,48)in accordance with Table 3;

Detail resolution detail indicator resolution value 15 100 14 91 13 83 12 74 11 65 10 57 9 48 8 39 7 31 6 22 5 13 4 5 3 0 2 0 1 0 0 0 Table 3 For example, if 10 dark regions are observed in the display video image of series 42 a detail resolution value of 57 is assigned.

Next, motion is simulated as described previously with reference to Figure 3c. From the motion simulation it is possible to determine the delay between the video camera 12' monitoring an event and the generation of a display video image comprising that event at t

video delay delay in nis Video delay value 0 100 < 50 100 < 100 90 < 200 80 < 300 60 < 400 30 < 500 10 > 500 0 Table 4 For example, if the delay between the simulation of an event monitored by video camera 12' and the subsequent generation of the corresponding display video image is 125ms then a video delay value of 80 is assigned.

Next, it is determined if breaks in audio data generated at a remote terminal occur, the audio data corresponding to an event monitored by the transmission portion 10'. An audio break value is assigned in accordance with Table 5 below;

udio breaks noticeable effects audio break value no audio breaks 0 breaks, still -10 understandable breaks, not -100 understandable Figure 5 For example, if breaks have occurred in the audio data, but the content of the audio data can be comprehended by the user a audio break value of -10 is assigned.

Next, the delay between the generation of audio data from apparatus monitoring an event and the generation of corresponding audio data comprising that event at the remote terminal is determined. An audio delay value is assigned is accordance with Table 6 below;

Audio delay delay in ms Audio delay value O j 100 < 50 100 < 100 90 < 200 80 < 300 60 < 400 30 < 500 10 > 500 0 Table 6 For example, if the delay between the generation of audio datc from a monitored event and the subsequent generation of thc corresponding audio data at the remote terminal is also 125mc then a audio delay value of 80 is assigned.

Next, referring to the apparatus of Figure 4, synchronisation ol the audio data and video data corresponding to a display videc image of an event monitored by the transmission portion 10' ic determined. The synchronisation delay between the generation oi audio data corresponding to video data for a display video image of a monitored event, or between the generation of audio datc and the subsequent generation of a display video image from th( video data corresponding to a monitored event can be determinec by the user. This synchronisation delay, or li1 synchronisation, is assigned a synchronisation value ii accordance with Table 7 below;

Lip synchronisation delay in ms synchronisation value O 100 < 50 100 < 100 90 < 150 80 < 200 70 < 250 50 < 300 30 < 400 10 > 400 0 Table 7 For example, if the delay between the generation of audio data from a monitored event and the generation of the corresponding video data is 220ms then a synchronisation value of 50 is assigned.

Further values can be assigned for comfort factors or features of the video communication system that the user may consider advantageous. For example, a set-up value may be assigned in accordance with the period that the video communication system required for preparation for receiving and/or transmitting data signals as shown in Figure 8 below;

Connection set-up tin- set-up time inset-up value seconds O 100 < is 100 < 2s 90 < 3s 80 < 4s 70 < 5s 50 < 6s 30 < 7s 10 > 7s 0 Table 8 For example, if the set-up period for preparing the videc communication system for each transmission and or receipt of data signals were 3.5 seconds a set-up value of 70 is assigned.

Similar comfort factors may have values assigned for use with the video communication benchmark (VCB) of the invention, each vale being assigned according to the usability of the videc communication system; For example, the reliability of the connection between thc transmission portion 10' and the receiving portion 10'' may be defined in terms of a reliability value (as illustrated in Table 9) such that where the period for maintaining a reliable connection were 26 minutes a reliability value of 30 is assigned;

Connection reliability connection time in reliability value n > 60 100 > 45 80 > 30 50 > 15 30 > 10 10 > 5 5 > 1 0 < 1 0 Table 9 Similarly, for example, the operational characteristics of the hardware of the video communication system may be defined ir terms of a hardware value (as illustrated in Table 10) such that where the hardware comprised 2 ISA buses a hardware value of 8C is assigned;

Hardware reau i remen t 5 board hardware value 1 PCI 100 1 ISA 100 2 ISA 80 3 ISA 50 each full size -10 card Figure 10 Similarly, for example, the operational characteristics of the software of the video communication system may be defined in terms of a software value (as illustrated in Table 11) such that where the software comprised "Windows 95" (registered Trade Mark of the Microsoft Corporation) a software value of 40 is assigned;

Software requirements supported OS software value Windows 3.1, 50 3. 11 Windows 95 40 Windows NT 20 OS/2 10 Figure 11 Weighting factors can be assigned to the video communication system in accordance with the operational environment being monitored by the transmitting portion 10'. For example, if the video camera 12' of the transmitting portion 10' is monitoring an event where comprising extreme motion (as may occur in a video-conference of a meeting) the data rate of the video data is large and requires greater compression. As has been described previously herein, video data comprising extreme compression can result in "dropped" frames, loss of resolution, and loss of synchronisation between the video data and the audio data. The weighting factor are assigned according to the criteria illustrated in Figure 12 below;

WEIGHTING FACTOR CONDITION A 2 No movement simulation, high resolution (e.g. image of a document) CONDITION B 3 Average movement, medium resolution (e.g. image of a single person) CONDITION C Extreme movement, high resolution (e.g. image of group of persons in a meeting) Figure 12 Finally, the values obtained are produced in a Table 13 indicative of the a particular test condition. A potential purchaser of a video communication system can view the results produced in the table to determine whether the video communication system is suitable for the required operational environment.

Weight Min Typical Max Total Results according to tables Condition Result 2620 Quality Result 2 -190 0 1000 2000 Video Quality 1 -90 0 600 600 Frame Rate 3 -30 100 Table #1A,B,C and #2 Dropped Frames 3 -30 0 0 Table &num;2 Detail 2 0 100 Table &num;3 Resolution Video Delay 1 0 100 Table &num;4 Audio Quality 1 -100 0 100 100 Audio breaks 1 -100 0 Table &num;5 Audio delay 1 0 100 Table &num;6 System Quality 1 0 0 300 300 Lip- 3 0 100 Table &num;7 Synchronisation Reliability/ 1 20 0 620 620 Usability Connection 2 0 0 200 400 Set-up time 1 0 100 Table &num; 8 Reliability 1 0 100 Table &num; 9 Platforms 1 20 0 220 220 Hardware 1 20 100 Table &num;10 Software 1 0 120 Table &num;11 Standards 1 0 200 200 User interface 1 0 100 100 Installation 1 0 30 30 Figure 13 Inserting the video communication benchmark values into Table 13 results in Table 14 in which:

Weight Min Typical Max Total Results according to tables Condition Result 1976 Quality Result 2 -190 663 1000 1326 Video Quality 1 -90 443 600 443 Frame Rate 3 -30 90 100 270 Table #lA,B,C & &num;2 Dropped Frames 3 -30 -7 0 -21 Table &num;2 Detail 2 0 57 100 114 Table &num;3 Resolution Video Delay 1 0 80 100 Table &num;4 Audio Quality 1 -100 70 100 70 Audio breaks 1 -100 -10 0 Table #5 Audio delay 1 0 80 100 Table &num;6 System Quality 1 0 150 300 150 Lip- 3 0 50 100 150 Table &num;7 Synchronisation Reliability/ 1 20 650 620 650 Usability Connection 2 0 0 100 200 200 Set-up time 1 0 70 100 Table &num; 8 Reliability 1 0 30 100 Table # 9 Platforms 1 20 120 220 120 Hardware 1 20 80 100 Table &num;10 Software 1 0 40 120 Table &num;11 Standards 1 0 200 200 User interface 1 0 100 100 Installation 1 0 ~ ~ 30 30 Table 14 It can be seen from the Table 14 that VCB values for the video quality of the video communication under appraisal comprise the frame rate value, the dropped frame value, the resolution value, and the video delay value. Similarly, VCB values for the audio quality of the video communication system under appraisal comprise the audio break value and the audio delay value, and the VCB value for the system quality comprises the synchronisation value. The overall VCB quality value for the video communication system under appraisal is derived from the sum of the video quality value, audio quality value, and the system quality value.

A VCB connection value is derived from the set-up value and the connection reliability value. The VCB connection value is indicative of the quality of the electrical and operational connections of the video communication system. Therefore, a video communication system that requires considerable effort to establish a connection with a remote terminal to which it is to transmit and receive audio and video data, or in which a connection once established is unreliable will have a low VCB connection value.

The VCB platform value is derived from the hardware value and the software value. The VCB platform value is indicative of the arrangement of the video communication system. For example, the video communication system may be a sub-system of a personal or mainframe computer comprising one or more add-on integrated circuit cards. Additionally, the video communication system may be capable of operating under one of a number of software operating systems or with a number of types of computer hardware.

The VCB platform value is greater where the video communication system requires few connection slots, and is compatible with the operation of a large number of software operating systems or computer hardware configurations. Therefore, a high VCB platform value is indicative of a video communication system that is supported by more than one software operating system, is compatible with the operation the hardware of more than one computer, and requires a limited number of connection slots to the electronic circuitry of the computer hardware.

Further VCB values can be assigned to different factors that may contribute to the operation of the video communication system under appraisal. For example, the video communication standard to which the video communication system complies may be one factor, the type of user interface (e.g. keyboard, mouse, type of video camera), or the installation requirements of the video communication (e.g. provision of an ISDN telephone connection) may all be assigned VCB values in accordance with the importance of the factor to the operational performance of the video communication system.

Therefore, it will be appreciated by the skilled person that the Video Communications Benchmark Values, together with the factors considered in calculating the quality of the video communication system being appraised by provided herein merely by way of illustration. Many further factors and features that effect the operational performance of the video communication system may be introduced into the calculation of the quality of the system being appraised. It should be further understood that the values provided in the Tables 1-14 and in the calculations illustrating the invention are likewise provided merely for the purposes of illustrating the method of the invention.

In an alternative embodiment of the apparatus of the invention, the rings 36,38 of LED's may be replaced by an array of LED's.

Alternatively, the rings of LED's may be supplemented by the addition of an array of LED's. This has been found to overcome problems associated with the ring of LED's where the codec of the video communication system being appraised compresses more than one frame of the video image together.

In a further alternative embodiment of the apparatus of the invention, the series of light and dark regions may comprise an array of lines or dots. Preferably the light or dark regions have an increased breadth when compared to a first adjacent region, and a reduced breadth when compared to a second adjacent region.

Although the present invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made thereto without departing from the spirit and scope of the present invention as described herein.

Claims (18)

1. A method for defining the quality of a received video image in a video communication system, which method comprising; providing a first video image for determining the frame rate of the video image generated by the video communication system; providing a second video image for determining the resolution of the video image generated by the video communication system; and providing a third video image for determining the effect of motion on the frame rate and resolution of the video image generated by the video communication system.

2. The method as claimed in Claim 1, wherein the step of providing the third video image comprises generating an image having a predetermined level of motion.

3. The method as claimed in Claim 1 or Claim 2, wherein the step of providing the third video image comprises simulating motion of a video image in a video signal provided to said video communication system.

4. The method as claimed in any preceding claim, wherein the step of providing the first video image comprises generating an image from at least one ring of lamps.

5. The method as claimed in any preceding claim, wherein the step of providing the ring of lamps comprises providing a ring of lamps :representative of a video frame according to the PAL or NTSC standard.

6. The method as claimed in any preceding claim further comprising; illuminating the lamps sequentially.

7. The method as claimed in any preceding claim, wherein the step of providing the second video image comprises providing an alternate series of dark and light rings.

8. The method as claimed in any preceding claim, wherein the step of providing the third video image comprises providing an object having a defined series of motions.

9. The method as claimed in any preceding claim further comprising; determining the synchronisation between the audio and video components of the received video signal.

10. An apparatus for defining the quality of a received video image in a video communication system, which method comprising; means for providing a first video image for determining the frame rate of the video image generated by the video communication system; means for providing a second video image for determining the resolution of the video image generated by the video communication system; means for providing a third video image for determining the effect of motion on the frame rate and resolution of the video image generated by the video communication system.

11. The apparatus as claimed in Claim 10, wherein the third video image comprises an image having a predetermined level of motion.

12. The apparatus as claimed in Claim 10 or Claim 11 further comprising; means for simulating motion of a video image in a video signal provided to said video communication system.

13. The apparatus as claimed in any of Claims 10 to 12, wherein the means for providing the first video image comprises at least one ring of lamps.

14. The apparatus as claimed in Claim 13, wherein the ring of lamps is representative of a video frame according to the PAL or NTSC standard.

15. The apparatus as claimed in Claim 13 or Claim 14, wherein the lamps are illuminated sequentially.

16. The apparatus as claimed in any of Claims 10 to 15, wherein the means for providing the second video image comprises an alternate series of dark and light rings.

17. The apparatus as claimed in any of Claims 10 to 16, wherein the means for providing the third video image comprises an object having a defined series of motions.

18. The apparatus as claimed in any of Claims 10 to 17 further comprising; means for determining the synchronisation between the audio and video components of the received video signal.