Digital television programming data processing – digital TV, programming, data processing – HC network broadcasting industry
Recent years, digital technology has made considerable progress, M-JPEG, DV, DV50, and MPEG-2 compression format widely used in other digital TV programming. In order to produce high quality TV programs, people want to make use of digital technology, and to as format conversion, compression, decompression and re-image quality caused by data processing to minimize damage. Many radio and television organizations and experts on this issue in-depth study and the completion of a number of objective measurement, achieved good results.
Data processing on image quality Television image signal processing generally can be divided into quantitative coding, data compression, and compression format conversion, etc., these processes will have adverse impact on image quality.
Early in the development of digital TV technologies for the digital TV image quality evaluation, subjective evaluation method has been adopted. In recent years, Tektronix products PQA200 picture quality analysis system, can simulate the human visual system for objective measurement, subjective reproduction of visual assessment of the human eye to calculate the image quality of the PQR values, that is, the value of image quality ratio. PQR is 10, said that the human eye can clearly observe the damage to the image quality; PQR is 3, that the human eye can often be observed in image quality damage; PQR value of 1, that the human eye hardly feel the image quality damage .
Digital television programming in the data processing
In a related study, has used the image signal through three tests to test a variety of image formats PQR value. The first female head is a simple close-up, focus on the details of the performance of skin and hair; the second is a more complex game wheel, focusing on the performance of fast motion; third is often used to "campaign, and calendar" images, mainly the complex contains many saturated color images and fine image details. Table 1 lists a variety of formats on the measured signals of three test images show the PQR values.
Can be seen from Table 1, the high rate of data processing on the image quality is relatively small, of course, their equipment prices are relatively high, and require larger digital storage space. Low price DVCPRO
25 and the DV format, such as consumer devices, in the case of low bit rate can be obtained with BetacamSP equivalent image quality. DVCPRO
50 was a higher quality recording format, tests show that it can provide close to the level of image quality Digital Betacam. Similarly, the rate to 50Mb / s of MPEG-2
I frame format, the image also shows the level of quality equivalent to DVCPRO50.
How to avoid the adverse effects of data processing
In program production, the number of data processing is likely to adversely affect the image quality. In order to maintain the quality of digital video signals must note the following:
Digital TV program production data processing
(1) to avoid transcoding. If you want to enter a non-linear editing system is not compatible with the format of the program material, the material must first transcode non-code system can accept the format. There are M-JPEG, DV, MPEG-2
I convert between, and the MPEG-2I and MPEG-2
IBP transition between these transformations need to decode and then re-encoding. The decoding and re-coding necessary adverse impact on image quality. Table 2 is the DVCPRO
25 transcoding into M-JPEG image quality after the impact of PQR values. If you use a higher bit rate transcoding, adverse effects become smaller, but in order to increase the cost of digital storage space.
(2) to avoid the A / D and D / A converter. A / D converter involve sampling, quantization and encoding. Use low-pass filter before sampling the original signal filtering, to prevent high frequency signal generator frequency aliasing. Filter cutoff frequency is half the sampling frequency, the frequency response curve steep, it is affecting the quality of digital systems is an important factor that may cause the edge of the image signal overshoot or ringing, and the image is unclear and so the transition edge, which affect the original image clarity and fine sense of other characteristics. In the D / A conversion, but also by low-pass filter, which also would have an impact on image quality.
In quantitative, we must use rounded approach to the quantitative sample value, it will produce quantization error. Quantization error is specific to digital imaging system, the damage source, often called quantization noise, it will cause the waveform of image distortion and image false contour effect. A high quality image signal, after following the 8b quantify, quantify the signal to noise ratio of its maximum theoretical value of 59dB, of course, the actual value will be lower. The study showed that when the image signal after the two A / D and D / A conversion, signal to noise ratio decreased 3dB, the equivalent of more than analog tape copy generation losses. People listen to CD discs, often feel more stiff and strident voice, known as the "digital sound 'feel. After the digital image signal, will give a similar feel. Compared with the original analog images, digital images fine degree of softness seems to be worse. This also shows that digital television is not without cost.
In addition, the test also showed that a DV NLE system, to enter the analog composite or component analog video signal, then through the A / D or D / A converter, the output image quality will be significantly lower. For example, in DV NLE system with DV Input, DV output, PQR value of 4.89 is still normal; with DV input, Y / C output, PQR value rose to 6.52; with Y / C input, Y / C output PQR value rose to 7.28. Thus, A / D and D / A converter negative impact on image quality is relatively large.
(3) to avoid decompression and recompression. In the digital television program production in the format of a compressed image signal to another format and then extract the compressed image quality will be more obvious damage. For example, M-JPEG, DV and MPEG-2
I frame format conversion between, although both intra-conversion between compression formats, but because of their stream organization and macro block structure is different, it must first convert the baseband signal, and then coding to achieve the format conversion. MPEG-2, if necessary
I frame format into MPEG-2
IBP frame format, it must first convert the baseband signal, and then coding; and vice versa. The conversion will result in damage to the image quality. It is worth mentioning that, if the 4:2:2 sampling format of 4:1:1 or 4:2:0 sampling into the format, the image of the color clear
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