Apparatus for modifying pixel data stored in a random access memory

Claim 1

An apparatus for modifying data stored in a random access memory, the data corresponding to one or more rows of pixels of a stored image, the memory comprising a first memory (colour RAM) for storing a colour value for each pixel and a second memory (z-RAM) for storing a depth (z) value for each pixel, the apparatus comprising: - means for receiving input data defining addresses, colour values and depth (z) values for a series of pixels; - means for selecting each pixel in the series in turn and synchronously generating successive addresses, input colour values and input z-values; - means for applying the address of each selected pixel to address inputs of the z-RAM and colour-RAM; - means for reading from the z-RAM the current z-value for each selected pixel; - means for comparing the current z-value with the input z-value for each selected pixel; - means for writing the input z-values for each selected pixel into the addressed location of the z-RAM and for writing the input colour values into the addressed location of the colour-RAM, said means being responsive to an output of the comparing means so as to enable the writing of the input colour value into the colour-RAM and the input z-value into the z-RAM, to define a new colour value and a new z-value for a given selected pixel if the input z-value represents a lesser depth than the current z-value for that pixel; characterised in that the z-RAM comprises a main random access array and a serial access memory and in that the apparatus further comprises means responsive to the input data for transferring the z-values for all pixels in the series from the main array of the z-RAM into the serial access memory of the z-RAM so that in operation, while the input values for the given pixel are being written into the colour-RAM and the main array of the z-RAM, the means for reading the current z-value is enabled to read the current z-value of a succeeding pixel in the series from an output of the serial access memory.

Claim 2

An apparatus for modifying data stored in a random access memory, the data corresponding to one or more rows of pixels of a stored image, the memory comprising a first memory (colour RAM) for storing a colour value for each pixel and a second memory (z-RAM) for storing a depth (z) value for each pixel, the apparatus comprising: - means for receiving input data defining addresses, colour values and depth (z) values for a series of pixels; - means for selecting each pixel in the series in turn and synchronously generating successive addresses, input colour values and input z-values; - means for applying the address of each selected pixel to address inputs of the z-RAM and colour-RAM; - means for reading from the z-RAM the current z-value for each selected pixel; - means for comparing the current z-value with the input z-value for each selected pixel; - means for writing the input z-values for each selected pixel into the addressed location of the z-RAM and for writing the input colour values into the addressed location of the colour-RAM, said means being responsive to an output of the comparing means so as to enable the writing of the input colour value into the colour-RAM and the input z-value into the z-RAM, to define a new colour value and a new z-value for a given selected pixel if the input z-value represents a lesser depth than the current z-value for that pixel; characterised in that the z-RAM comprises a main random access array and a serial access memory and in that the apparatus further comprises means responsive to the input data for transferring the z-values for all pixels in the series from the main array of the z-RAM into the serial access memory of the z-RAM so that in operation, while the input values for the given pixel are being written into the colour-RAM and the main array of the z-RAM, the means for reading the current z-value is enabled to read the current z-value of a succeeding pixel in the series from an output of the serial access memory.

Claim 5

An apparatus as claimed in any of Claims 1 to 3 wherein the comparing means comprises a digital comparator having a first input connected to the means for generating the successive input z-values and a second input for connection to the output of the serial access memory of the z-RAM.

Claim 7

An apparatus as claimed in any of Claims 1 to 5 comprising one or more clocked latches for synchronising data applied to the colour-RAM and z-RAM with the signals applied to the address inputs of the colour-RAM and z-RAM respectively and with signals applied to control inputs of those RAMs.

Claim 8

An apparatus as claimed in any of Claims 1 to 6 comprising a sequencing circuit for applying control signals to the colour-RAM and z-RAM synchronously with the selection of the pixels of the series.

Claim 9

An apparatus as claimed in any of Claims 1 to 7, wherein the colour-RAM comprises a main random access array and a serial access memory, the means for writing the input colour values into the colour-RAM being arranged for connection to the main array of the colour-RAM, the apparatus further comprising a picture output arranged for connection to the output of the serial access memory of the colour-RAM.

Claim 10

An apparatus as claimed in any of Claims 1 to 8, wherein the colour-RAM and z-RAM comprise one or more identical integrated circuit memories.