Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N17/00—Diagnosis, testing or measuring for television systems or their details
  • H04N17/04—Diagnosis, testing or measuring for television systems or their details for receivers
  • H04N17/045—Self-contained testing apparatus

Definitions

• the invention relates to a method and a system for testing the ability of an apparatus to produce faultless video and / or audio signals encoding images and / or sounds.
• the invention also relates to an information recording medium containing instructions for implementing the test method. More specifically, the invention relates to a test method comprising a step of applying, at the input of the device, a reference sequence capable of imposing the content of the video and / or audio signal produced at the output of the device. .
• Such methods are particularly useful for testing the quality of the video and / or audio signals produced by apparatuses such as televisions, decoders of digital television channels, video recorders, computers and other types of apparatus capable of producing. video and / or audio signals.
• apparatuses such as televisions, decoders of digital television channels, video recorders, computers and other types of apparatus capable of producing. video and / or audio signals.
• a decoder it is connected at the input to a stream generator and at the output to a television.
• the stream generator is configured to transmit a reference sequence to the decoder so that the decoder outputs a video and audio signal containing a still image and sounds.
• This still image is then displayed by the TV and the sounds are generated by the TV speakers.
• this still image is constructed so as to highlight certain types of defect likely to exist in the video signal produced by the decoder.
• this still image corresponds to the test pattern that televisions broadcast outside of program hours. Then, this test pattern and the generated sounds are compared manually, by an operator, to a reference test pattern and to reference sounds. Thanks to such a method, defects in the transcription of the colors of the image and of the sounds can be detected. However, the precision of such a test is limited by the operator's ability to discern nuances of color and / or sound between them and therefore remains largely subjective.
• the invention aims to remedy this drawback by proposing an independent test method for the ability of an operator to distinguish between them different shades of colors and / or sounds.
• the subject of the invention is therefore a test method as described above, characterized in that an electronic computer further carries out: - a step of acquiring the video and / or audio signal actually produced by the device in response to the reference sequence, - an automatic step of analyzing the acquired video and / or audio signal to establish the value of at least one characteristic of the images and / or sounds contained in the signal to be analyzed, and - a step comparison of the value established for the or each characteristic with at least one predefined threshold for the same characteristic, so as to automatically establish the presence of a fault.
• an electronic computer during an analysis step, at least one characteristic of the images and / or sounds contained in the audio and / or video signal is measured by an electronic computer.
• the characteristic measured is expressed in an encrypted form.
• the value of the measured characteristic is compared with a value or with a predefined range of values acceptable for this same characteristic. Consequently, since in this process, only numerical values are compared with other numerical values, the ability of an operator to discern different shades of colors no longer intervenes. Therefore, it is possible to determine much more precisely the existence of a defect in the video and / or audio signals analyzed.
• the method according to the invention is characterized in that: - it includes an operation of reading in the signal to be analyzed an identifier of the reference sequence to automatically identify the reference sequence applied to the input of the device to be tested; - during the application step, several different reference sequences may be applied at the input of the device to be tested, each reference sequence being intended to be analyzed using a specific analysis method during the analysis step, and in that the operation reading the sequence identifier is followed by an automatic verification operation of the correspondence between the identifier of the reference sequence read and the analysis method currently used; - It includes a reading operation in the signal to be analyzed of an image identifier to automatically identify an image among several images present in the signal to be analyzed; - It includes a step of automatically detecting the slowing down or stopping of the scrolling of a temporal succession of images contained in the signal to be analyzed; the detection step comprises an operation of reading the image identifier at different times in the signal to be analyzed, an operation of comparing the value of the image identifier
• the invention also relates to an information recording medium containing instructions for the execution of the method according to the invention when these instructions are executed by an electronic computer.
• the subject of the invention is also a system for testing the ability of an apparatus to produce without defect a video and / or audio signal containing coded images and / or sounds, this system comprising: - application means , at the input of the device, of a reference sequence capable of imposing the content of the video and / or audio signal produced at the output of the device, characterized in that it comprises an electronic computer equipped with: - a module for acquiring the video and / or audio signal actually produced by the device in response to the reference sequence, - a module for automatic analysis of the acquired video and / or audio signal to establish the value of at least one characteristic images and / or sounds contained in the signal to be analyzed, - a module for comparing the value established for the or each characteristic with at least a predefined threshold for the same characteristic so as to automatically establish the presence of a fault .
• FIG. 1 is a schematic illustration of the architecture of a system of test according to the invention
• - Figure 2 is a flow diagram of a test method according to the invention
• - Figure 3 is a schematic illustration of a particular type of test pattern used in the method of Figure 2
• - Figures 4a to 4c are examples of a histogram analysis of the test pattern of Figure 3.
• Figure 1 shows a test system 2 of a device 4 capable of producing video and / or audio signals .
• the description of the system 2 is given here, by way of example, in the particular case where the device 4 is a conventional decoder for digital television channels.
• the decoder is capable of receiving, as input, digital signals containing coded images and sounds corresponding to different channels of television.
• the decoder 4 is capable of producing video and audio signals intended for a conventional television set.
• System 2 includes a conventional stream generator 10 capable of generating a television signal identical to that produced, for example, by a satellite for retransmission of television channels. More specifically, the generator 10 outputs a signal in which the images and sounds corresponding to several television channels are multiplexed.
• this output of the generator 10 is connected, via a conventional satellite modulator 12, to the input of a conventional test bench 14.
• the test bench 14 is capable of delivering to the input of the decoder 4 the television signal which the decoder must transcribe into a video and audio signal suitable for being displayed on a conventional television set.
• the test bench is also capable of configuring the decoder 4, and for example, of selecting a specific television channel.
• the generator 10 produces the television signal from reference sequences prerecorded in a memory 16 associated with this generator. Each reference sequence is here specially constructed to test one or more characteristics of the device 4.
• the output of this decoder 4 is connected to an input of the bench. test.
• the test bench 14 is also connected to an electronic computer, here a computer 20, for delivering to the latter the video and audio signals produced by the decoder 4.
• the computer 20 comprises a central unit 22 as well as a human / machine formed here by a screen 24 and a keyboard 26.
• the central unit 22 is equipped with an acquisition card 28 for converting the audio and video signals transmitted by the test bench 14 into digital signals suitable for being processed by the computer 20.
• the central unit 22 also includes a module 30 for analyzing and comparing the signals acquired by the card 28, a module 32 for acquiring information entered using the keyboard 26, a module 34 d display and a module 36 for controlling the test bench 14.
• the module 36 is, for example, capable of selecting a new reference sequence by commanding a change of television channel.
• the analysis module 30 is capable of analyzing the video and / or audio signal acquired by the card 28 by implementing one of the following methods: - a method of analysis of the signals acquired using histograms , - a direct analysis method in which the information relating to each pixel or sample of sounds is compared pixel by pixel or sample of sounds by sample of acquired sounds to the information which should have been obtained if the video and / or audio signal was free of defects, and - a method of spectral analysis of the acquired signal.
• the acquired video signal is a digital video signal in which the color of each pixel is defined by a triplet of digital values denoted respectively Y, Cr and Cb.
• the histogram analysis of the digital video signal consists in constructing for each image or for a succession of images contained in the digital video signal three histograms such as those represented in FIGS. 4a to 4c.
• the abscissa of the histograms of FIGS. 4a to 4c comprises the set of possible values respectively for the luminance, the red chrominance and the blue chrominance.
• the ordinate axis of these histograms represents a number of pixels.
• spectral analysis consists in constructing a spectrum associated with an image or a succession of images or even with a sound from the series of digital values coding these images or these sounds in the video signal and / or acquired audio.
• a spectrum can be associated with a sequence of numbers encoding a sound using a discrete fourier transform.
• the same method is also applied to sequences of numbers coding the color of each pixel.
• the central unit 22 is produced from a conventional programmable microprocessor capable of executing instructions recorded on an information recording medium. To this end, the central unit 22 is associated with the memory 16 and this memory 16 includes instructions for the execution of the method of FIG. 2 when these instructions are executed by the central unit.
• the memory 16 is also here intended to contain all the parameters useful for the execution of the method of FIG. 2. To adapt the system 2 to other types of apparatus, it suffices to replace the generator 10, the modulator 12 and possibly the test bench
• the computer 20 and the central unit 22 are described in the case where different types of apparatus can be tested.
• the decoders of digital television channels, the decoders of analog television channels, televisions, mobile telephones each correspond to a different type of device to be tested.
• the operation of the system will now be described with reference to FIG. 2.
• the method of FIG. 2 mainly consists of a phase 50 of preparation of the reference sequences for each type of device to be tested and of a phase 52 of actual device test.
• phase 50 is to construct, during a step 58, the reference sequences to be recorded in the memory 16, each sequence being intended to best reveal the faults of the device to be tested.
• at least one of the reference sequences will scan the whole range of audible sounds and / or the whole range of colors displayable by the device to be tested.
• one of the reference sequences recorded in the memory 16 is constructed so that, in response to this sequence, the video signal produced by the apparatus to be tested contains a test pattern 60 represented in FIG. 3.
• this test pattern 60 will be described using the convention according to which the color of each pixel forming the test pattern is associated with the triplet of numerical values, denoted respectively Y, Cr and Cb.
• Target 60 is designed to test for possible defects related to the movement of objects in a scene as well as to determine the offset and the format of the image.
• the test pattern 60 is constructed so as to simplify the histogram analysis of the video signal produced.
• the rectangular bottom 61 of the test pattern 60 forming the background is of uniform color.
• This background 61 is here gray in color and coded by the value triplet (128, 128, 128).
• this background 61 must generate a color peak in each of the three histograms of FIGS. 4a to 4c near the value 128.
• Four squares 62 to 65 of uniform color are drawn near each of the angles of the bottom 61. The dimensions as well as the color of each square are constant.
• each of these squares is chosen so as to correspond to an identifiable color peak in at least one of the three histograms of FIGS. 4a to 4c.
• the colors of the squares 62 to 65 are respectively coded by the triples (70, 128, 128), (128, 70, 128), (128, 128, 70) and (180, 180, 180).
• the square 62 creates an identifiable color peak around the value 70 in the histogram of FIG. 4a.
• This square 62 also creates 2 peaks of color around the value 128 in the histograms of FIGS. 4b and 4c. These peaks of color are added with that created by the background 61 and are therefore not identifiable.
• each square is animated by a cyclic movement.
• each of these squares periodically describes a closed rectangular path represented in FIG. 3 by arrows.
• This route is chosen so that the surface of the square, during these movements, never overlaps with other colored patterns of the same picture.
• the number of colored pixels forming a square is constant and the ratio of this number of colored pixels forming a square to the number of colored pixels of the background 61 is also constant.
• each reference sequence an identifier of the reference sequence and an identifier of each image of the reference sequence are embedded, during an operation 66, in each of the images of this sequence.
• two vertical bar codes 68 and 69 are embedded on the right and left of the center of the test pattern 60.
• Each of these bar codes 68, 69 represents the same identifier of a specific image among the succession of images that contains the reference sequence corresponding to the test pattern 60.
• these bar codes 68 and 69 each include ten horizontal bars. Each bar is, for example, either black or white.
• a black bar corresponds to an information bit equal to 0 while a white bar corresponds to an information bit equal to 1.
• the color code used for the bar code 69 is inverted compared to that used for bar code 68.
• a black bar in bar code 69 corresponds to an information bit equal to 1
• a white bar corresponds to an information bit equal to 0.
• the colors black and white correspond respectively to the triplets (20, 128, 128) and (230, 128, 128).
• the test pattern 60 also includes two vertical bar codes 70 and 72 each making it possible to identify the reference sequence. These bar codes 70 and 72 are located respectively to the left of the bar code 68 and to the right of the bar code 69. Each of these bar codes 70, 72 is formed by four bars, either white or black depending on the value of the information bit they represent.
• Target 60 also includes a white vertical rectangle 73a surrounded by a black border 73b.
• the geometric center of this rectangle 73a is located exactly at the geometric center of the test pattern 60.
• the height and the width of this rectangle 73a are known. The interest of this rectangle 73a will appear on reading the following description.
• each reference sequence associated with the identifier of this sequence, is recorded in the memory 16 during an operation 74.
• each reference sequence constructed is associated, during a step 76, with the nature of the defect that it is intended to test and with a method of analysis of the video and / or audio signals produced by the device to be tested in response to this reference sequence.
• the analysis method associated with each reference sequence is here chosen not only as a function of the reference sequence but also as a function of the type of device and of detailed information on the device to be tested.
• the detailed information of a device includes the name of the manufacturer, the reference of the model, its version as well as any other information likely to influence the quality of the audio and / or video signals produced.
• the relationship between the analysis method, the identifier of the reference sequence, the nature of the fault to be tested, the type of device to be tested and the detailed information on this device is recorded, during of an operation 78, in a relational database contained in the memory 16.
• reference devices are tested, during a step 80, to define values or ranges of values acceptable for each type of device based on detailed information on that device.
• Each reference device used is considered to represent the reference in terms of quality of video and / or audio signals produced.
• each reference device is mounted in place of the device to be tested and the reference sequences are applied to the input of this reference device.
• the video and / or audio signals produced by the reference device are then analyzed using the analysis methods corresponding to the reference sequence applied.
• characteristics representative of the quality of the video and / or audio signals produced are measured. For example, during a histogram analysis, the position and amplitude of the peaks on each of the histograms in FIGS. 4a to 4c are measured and recorded. Then, the values recorded for several identical reference devices are processed statistically to obtain, for each measured characteristic, a maximum acceptable threshold and a minimum threshold. These minimum and maximum thresholds define a range of values within which any device, free of faults, must be located.
• these thresholds are recorded in the memory 16 so that, for each characteristic, the computer 20 can quickly find them as a function of the identifier of the reference sequence, the analysis method used, the type of device to be tested and detailed information about this device.
• maximum and minimum thresholds are defined for each value indicated on the abscissa of the histograms of FIGS. 4a to 4c.
• the minimum and maximum thresholds are represented by lines respectively in fine lines and in dotted lines, on the histograms of FIGS. 4a to 4c. Note that thanks to the specific characteristics of the target
• these maximum and minimum thresholds are constant whatever the image to be analyzed in the video signal produced by the apparatus to be tested.
• these thresholds are independent of the displacements of the squares 62 to 65 and of a modification of the value of the image identifier and / or reference sequence.
• the test phase 52 can begin.
• the computer acquires during a step 90, via the man / machine interface, the type of device to be tested as well as the detailed information relating to it.
• the information acquired corresponds to the decoder 4.
• the computer also acquires the nature of the fault or faults to be tested.
• the reference sequence or sequences used to test the decoder 4 are applied to the input of this decoder.
• the module 36 automatically selects, during an operation 94, the reference sequence or sequences to be used as a function of the information acquired during step 90 and activates the corresponding analysis method or methods.
• the reference sequence selected is that described with reference to FIG. 3 and that the activated analysis method is the histogram analysis method.
• the decoder 4 outputs, during a step 96, audio and video signals which are transmitted via the test bench 14 to the acquisition card 28.
• the acquisition card 28 converts, during a step 98, these audio and video signals into a digital format suitable for the processing of the module 30.
• the module 30 then proceeds to a step 100 of verifying the synchronization of the analysis methods with the signal to be analyzed transmitted by the acquisition card 28.
• the module 30 reads, during an operation 102, the identifiers of the reference sequence used for this test. For example, the module 30 reads the bar codes 70 and 72 so as to determine the value of the identifier of the reference sequence. Once the identifier of the reference sequence has been obtained, the module 30 automatically verifies, during an operation 104, that the currently activated analysis method corresponding to this identifier and to the type of device to be tested.
• the module 30 verifies that the histogram analysis method is activated. If the identifier of the sequence of reference read, does not correspond to the activated analysis method, the method returns to step 92. Otherwise, the method continues with a step 106 of processing each image or of a succession of contained images in the signal to be analyzed using the analysis method selected during operation 94. For example, during step 106, the module 30 constructs, for each image, the histograms of FIGS. 4a to 4c. By way of illustration, the values of the histograms constructed for one of these images are shown in bold lines in FIGS. 4a to 4c.
• the module 30 compares, during a step 110, the values measured or established during the step 106 to thresholds to determine the presence of a defect in the image or the sound contained in the analyzed signal.
• the module 30 automatically selects, in the memory 16, the thresholds to be used according to: - the identifier of the reference sequence read during the operation 102, - the type of apparatus to be tested and detailed information concerning it acquired during step 90, - of the analysis method used during step 106.
• the module 30 selects the minimum and maximum thresholds represented respectively by dashed lines and fine lines on the histograms of Figures 4a to 4c.
• the module 34 displays, during a step 120, a message indicating that a fault has been detected. Otherwise, this process continues by analyzing the following image coded in the analyzed video signal and returns to step 106. If no fault has been detected during the course of the entire reference sequence, a new reference sequence is selected during a step 122, and the method returns to step 92. If the device 4 is capable of producing faultless audio and video signals, the process ends without any message indicating a fault having been displayed on the screen 24.
• the comparison operation 114 results in detecting a display fault in the color of the square 65, as well as a display fault in the color of the square 63, visible on the histograms of FIGS. 4a and 4b.
• the module 30 proceeds to a step 130 of detecting a slowing down or stopping of the scrolling of the time sequence of images contained in the video signal produced by the decoder 4. For this purpose, the module 30 reads the bar codes 68 and 69, at regular time intervals, during an operation 132, in the video signal to be analyzed.
• the module 30 interrupts, during a step 136, the test phase 52 and then proceeds to step 120 for displaying a fault. Also in parallel with step 100, the module 30 automatically checks, during a step 140, the centering and the format of the images produced by the decoder 4.
• the module 30 measures, during an operation 142, the position of the geometric center of rectangle 73a as well as its vertical and horizontal dimensions in one or more images.
• the module 30 detects the edges of the rectangle 73a from the sudden change in color between the border 73b and the rectangle 73a. Then, during an operation 144, the module 30 compares the measured position of the center of the rectangle 74a to a predefined position of this same rectangle when the image is perfectly centered. It thus establishes a horizontal offset and a vertical offset of the analyzed image.
• the module 30 also compares, during an operation 146, the dimensions of the rectangle 73a to predefined dimensions for this same rectangle in different standard display formats.
• standard display formats are, for example, the formats known under the terms of 16/9 and 4/3.
• this information is, for example, used by the module 36 which controls a change in the display format of the decoder 4 or an adjustment of the horizontal and vertical offset of the image via the test bench 14.
• the method of FIG. 2 has the advantage of being entirely automatic.
• the three histograms of FIGS. 4a to 4c are constructed for each image of the reference sequence.
• the histograms of FIGS. 4a to 4c are constructed only for some of the images of the reference sequence.
• the reference sequence is a series of commands applied to this autonomous device so that it it outputs the video and / or audio signals corresponding to the commands received.
• An example of such a stand-alone device is for example a mobile telephone equipped with a screen on which various menus can be displayed.
• the reference sequence described here has two distinct identifiers, one to identify the sequence and the other to identify each image of this sequence. However, as a variant, a single identifier is used to identify both the sequence and the image in this sequence.
• the most significant bits will be used to identify the sequence, while the least significant bits will be used to identify the image in this sequence.
• Identifiers have been described here as bar codes embedded in an image.
• the identifier is a particular frequency and predefined in advance contained in the audio signal.
• the area of squares 62 to 65 has been described here as being constant. However, as a variant, this may vary from one image to another.
• the predefined thresholds used for the histogram analysis are modified as a function, for example, of the image identifier read.
• the method of FIG. 2 was described in the particular case where it is interrupted only in the case where a stop or a slowing down of the scrolling of the images is detected.
• the method is adapted to accumulate the number of detected faults and to stop automatically as soon as this cumulative number of faults exceeds a predetermined threshold.
• the method of FIG. 2 has been described in the particular case where the centering and the format of the images determined during step 140 are only used during a step 148 to control a change of display format.
• the information collected during this step 140 and in particular, the information concerning the centering of the image is used during the processing of each image or sequence of images to: identify the position of the bar codes 68 to 72, - identify the position of the squares 62 to 65 in each image, and - configure the analysis methods used.

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• Engineering & Computer Science (AREA)
• Health & Medical Sciences (AREA)
• Biomedical Technology (AREA)
• General Health & Medical Sciences (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Testing, Inspecting, Measuring Of Stereoscopic Televisions And Televisions (AREA)

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• 2004
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