Gamma Corrector IP Core 15

2015.01.23

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The Gamma Corrector IP core corrects video streams for the physical properties of display devices.

The Gamma Corrector IP core provides a look-up table (LUT) accessed through an Avalon-MM slave port. The gamma values can be entered in the LUT by external hardware using this interface.

For example, the brightness displayed by a cathode-ray tube monitor has a nonlinear response to the voltage of a video signal. You can configure the Gamma Corrector with a look-up table that models the nonlinear function to compensate for the non linearity. The look-up table can then transform the video data and give the best image on the display.

Gamma Corrector Parameter Settings

Table 15-1: Gamma Corrector Parameter Settings

You program the actual gamma corrected intensity values at run time using the Avalon-MM slave interface.

Parameter			Value		Description
Bits per pixel per color plane		4–16, Default = 8			Select the number of bits per pixel (per color
					plane).
Number of color planes		1–3, Default = 3			Select the number of color planes that are
					sent in sequence or parallel over one data
					connection.
Color plane transmission format		•	Color planes in		Select whether to transmit the specified
			sequence		number of color planes in sequence or in
		•	Color planes in		parallel. For example, a value of 3 planes in
					sequence for R'G'B' R'G'B' R'G'B'.
			parallel

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	15-2	Gamma Corrector Signals	UG-VIPSUITE
			2015.01.23

Gamma Corrector Signals

Table 15-2: Gamma Corrector Signals

Signal		Directio		Description
		n
clock		Input		The main system clock. The IP core operates on the
				rising edge of this signal.
reset		Input		The IP core asynchronously resets when this signal is
				high. You must deassert this signal synchronously to the
				rising edge of the clock signal.
din_data		Input		din port Avalon-ST data bus. This bus enables the
				transfer of pixel data into the IP core.
din_endofpacket		Input		din port Avalon-ST endofpacket signal. This signal
				marks the end of an Avalon-ST packet.
din_ready		Output		din port Avalon-ST ready signal. This signal indicates
				when the IP core is ready to receive data.
din_startofpacket		Input		din port Avalon-ST startofpacket signal. This signal
				marks the start of an Avalon-ST packet.
din_valid		Input		din port Avalon-ST valid signal. This signal identifies
				the cycles when the port must enter data.
dout_data		Output		dout port Avalon-ST data bus. This bus enables the
				transfer of pixel data out of the IP core.
dout_endofpacket		Output		dout port Avalon-ST endofpacket signal. This signal
				marks the end of an Avalon-ST packet.
dout_ready		Input		dout port Avalon-ST ready signal. The downstream
				device asserts this signal when it is able to receive data.
dout_startofpacket		Output		dout port Avalon-ST startofpacket signal. This signal
				marks the start of an Avalon-ST packet.
dout_valid		Output		dout port Avalon-ST valid signal. The IP core asserts
				this signal when it produces data.
gamma_lut_av_address		Input		gamma_lut port Avalon-MM address bus. This bus
				specifies a word offset into the slave address space.
gamma_lut_av_chipselect		Input		gamma_lut slave port Avalon-MM chipselect signal.
				The gamma_lut port ignores all other signals unless you
				assert this signal.
gamma_lut_av_readdata		Output		gamma_lut slave port Avalon-MM readdata bus. The IP
				core uses these output lines for read transfers.

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	Signal		Directio		Description
			n
	gamma_lut_av_write		Input		gamma_lut slave port Avalon-MM write signal. When
					you assert this signal, the reader control port accepts
					new data from the writedata bus.
	gamma_lut_av_writedata		Input		gamma_lutslave port Avalon-MM writedata bus. The IP
					core uses these input lines for write transfers.

Gamma Corrector Control Registers

The Gamma Corrector can have up to three Avalon-MM slave interfaces. There is a separate slave interface for each channel in parallel.

The control registers are read continuously during the operation of the IP core, so making a change to part of the Gamma look-up table during the processing of a frame always has immediate effect.

Note: The width of each register in the Gamma Corrector control register map is always equal to the value of the Bits per pixel per color plane parameter selected in the parameter editor.

When dealing with image data with N bits per pixel per color plane, the address space of the Avalon-MM slave port spans 2N + 2 registers where each register is N bits wide. Registers 2 to 2N + 1 are the look-up values for the gamma correction function. Image data with a value x will be mapped to whatever value is in the LUT at address x + 2.

Table 15-3: Gamma Corrector Control Register Map for Interface 0

	Address		Register		Description
0			Control		Bit 0 of this register is the Go bit, all other bits are unused.
					Setting this bit to 0 causes the IP core to stop the next time
					control information is read.
	1		Status		Bit 0 of this register is the Status bit, all other bits are unused.
	2 to 2N +1		Gamma Look-Up Table		These registers contain a look-up table that is used to apply
	where N is the				gamma correction to video data. An input intensity value of x
	number of bits				is gamma corrected by replacing it with the contents of the (x
	per color				+1)th entry in the look-up table. Changing the values of these
	plane.				registers has an immediate effect on the behavior of the IP
					core. To ensure that gamma look-up values do not change
					during processing of a video frame, use the Go bit to stop the
					IP core while the table is changed.
	Table 15-4: Gamma Corrector Control Register Map for Interface 1
	Address		Register		Description
0			Unused		This register is not used.
	1		Unused		This register is not used.
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	15-4		Gamma Corrector Control Registers				UG-VIPSUITE
						2015.01.23
			Address		Register		Description
			2 to 2N +1		Gamma Look-Up Table		These registers contain a look-up table that is used to apply
			where N is the				gamma correction to video data. An input intensity value of x
			number of bits				is gamma corrected by replacing it with the contents of the (x
			per color				+1)th entry in the look-up table. Changing the values of these
			plane.				registers has an immediate effect on the behavior of the IP
							core. To ensure that gamma look-up values do not change
							during processing of a video frame, use the Go bit in Interface
							0 to stop the IP core while the table is changed.
		Table 15-5: Gamma Corrector Control Register Map for Interface 2
			Address		Register		Description
			0		Unused		This register is not used.
			1		Unused		This register is not used.
			2 to 2N +1		Gamma Look-Up Table		These registers contain a look-up table that is used to apply
			where N is the				gamma correction to video data. An input intensity value of x
			number of bits				is gamma corrected by replacing it with the contents of the (x
			per color				+1)th entry in the look-up table. Changing the values of these
			plane.				registers has an immediate effect on the behavior of the IP
							core. To ensure that gamma look-up values do not change
							during processing of a video frame, use the Go bit in Interface
							0 to stop the IP core while the table is changed.

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