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TDA9178 Fiches technique(PDF) 9 Page - NXP Semiconductors |
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TDA9178 Fiches technique(HTML) 9 Page - NXP Semiconductors |
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9 / 36 page  1999 Sep 24 9 Philips Semiconductors Preliminary specification YUV one chip picture improvement based on luminance vector-, colour vector- and spectral processor TDA9178 SKIN TONE CORRECTION Skin tones are very sensitive for transmission (hue) errors, because we have an absolute feeling for skin tones. To make a picture look free of hue error, the goal is to make sure that skin tones are put at a correct colour. The dynamic skin tone correction circuit achieves this goal by instantaneously and locally changing the hue of those colours which are located in the area in the UV plane that matches skin tones (see Fig.4). The correction is dependent on luminance, saturation and distance to the preferred axis and can be done towards two different angles. The preferred angle can be chosen by bit ASK in the I2C-bus settings. The settings are 123 ° (ASK = 0) and 117° (ASK = 1). The enclosed correction area can be increased to 140% with the I2C-bus bit SSK (so-called: Size). The enclosed detection ‘angle’ of the correcting area can be increased to 160% with the I2C-bus bit WSK (so-called: Width). The skin tone correction can be switched on or off with the I2C-bus bit DSK. GREEN ENHANCEMENT The green enhancement circuit (see Fig.5) is intended to shift low saturated green colours towards more saturated green colours. This shift is achieved by instantaneously and locally changing those colours which are located in the area in the UV plane that matches low saturated green. The saturation shift is dependent on the luminance, saturation and distance to the detection axis of 208 °. The direction of shift in the colour is fixed by hardware. The amount of green enhancement can be increased to 160% by the I2C-bus bit GGR. The enclosed detection ‘angle’ of the correcting area can be increased to 160% with the I2C-bus bit WGR (so-called: Width). The enclosed correction area can be increased to 140% with the I2C-bus bit SGR (so-called: Size). The green enhancement can be switched on or switched off with the I2C-bus bit DGR. BLUE STRETCH The blue stretch circuit (see Fig.6) is intended to shift colours near white towards more blueish coloured white to give a brighter impression. This shift is achieved by instantaneously and locally changing those colours which are located in the area in the UV plane that matches colours near white. The shift is dependent on the luminance and saturation. The direction of shift (towards an angle of 330 °) in the colour is fixed by hardware. The amount of blue stretch can be increased to 160% by the I2C-bus bit GBL. The enclosed correction area can be increased to 140% by the I2C-bus bit SBL (so-called: Size). The blue stretch can be switched on or off by the I2C-bus bit DBL. SATURATION CORRECTION The non-linear luminance processing done by the histogram modification and variable gamma, influences the colour reproduction; mainly the colour saturation. Therefore, the U and V signals are linear processed for saturation compensation. Noise measuring A video line which is supposed to be free from video information (‘empty line’) is used to measure the amount of noise. The measured RMS value of the noise can be used for reducing several features, by the I2C-bus interface, such as luminance vector processing and spectral processing. For the TDA9178 the empty line is chosen three lines after recognition of the vertical blanking from the sandcastle pulse input. Figures 7, 8, 9 and 10 show the measurement locations for different broadcast norms. The noise detector is capable of measuring the signal-to-noise ratio between −45 and −20 dB. The output scale runs linearly with dB. The noise samples are averaged for over 20 fields to reduce the fluctuations in the measurement process. It is obvious, that for signal sources (like VCR in still picture mode) that re-insert the levels of the retrace part, the measurement is not reliable (see Section “Feature mode detector”). The result of the averaging process will update the contents of the I2C-bus register: bits ND5 to ND0 at a rate of 1 ⁄32 of the field frequency. If a register access conflict occurs, the data of the noise register is made invalid by setting the flag bit DV (Data Valid) to zero. Feature mode detector A detector is available for detecting signal sources (like VCR in still picture mode) that re-inserted the levels of the retrace part. For this kind of signals the noise measurement of the TDA9178 is not reliable, but this detector sets bit FM in the ND-register to logic 1. For normal video signals bit FM is set to logic 0. This circuit measures transients (like synchronization pulses) on the luminance input during the internal V-pulse. The feature mode detector is setting bit FM to logic 1 when no transients are present during 2 lines in the vertical retrace part over 3 fields (like the synchronization pulses). |
Numéro de pièce similaire - TDA9178 |
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Description similaire - TDA9178 |
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