Cached color conversion method and apparatus

• US 6,246,396 B1
• Filed: 02/18/1998
• Issued: 06/12/2001
• Est. Priority Date: 04/30/1997
• Status: Expired due to Term

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Gibson, Ian, Wong, Kevin Chee-Hoong
• Primary Examiner(s): Tung, Kee M.
• Application Number:
  US09/025,771
• Time in Patent Office: 1,210 Days
• Field of Search: 345/150, 345/153-155, 345/431, 345/186, 345/507-509, 345/513, 345/515, 345/516, 382/276, 382/167, 358/518, 358/519, 358/523-525, 358/1.9
• US Class Current: 345/604
• CPC Class Codes: G06F 17/147 Discrete orthonormal transforms, e.g. discrete cosine transform, discrete sine transform, and variations therefrom, e.g. modified discrete cosine transform, integer transforms approximating the discrete cosine transform G06F17/145 takes precedence
• CPC Class Codes: G06F 9/3879 for non-native instruction execution, e.g. executing a command; for Java instruction set
• CPC Class Codes: G06F 9/3885 using a plurality of independent parallel functional units
• CPC Class Codes: G06F 9/3897 with adaptable data path
• CPC Class Codes: G06T 1/20 Processor architectures; Processor configuration, e.g. pipelining
• CPC Class Codes: G06T 15/005 General purpose rendering architectures
• CPC Class Codes: G06T 2200/28 involving image processing hardware
• CPC Class Codes: G11C 7/1075 for multiport memories each having random access ports and serial ports, e.g. video RAM
• CPC Class Codes: H04N 19/42 characterised by implementation details or hardware specially adapted for video compression or decompression, e.g. dedicated software implementation H04N19/635 takes precedence
• CPC Class Codes: H04N 19/90 using coding techniques not provided for in groups H04N19/10-H04N19/85, e.g. fractals

Abstract

An apparatus for converting an input image in an input color space to an output image in an output color space.

The apparatus has a cache memory for storing from external memory, sparsely located output color values corresponding to input pixels closest to the current input pixel of an image stream, if not already present in the cache memory. The apparatus also has retrieval means for retrieving, from said cache memory, the sparsely located output color values corresponding to the current input pixel of the stream. The retrieved output color values are interpolated by interpolation means to derive an output color value in said output color space.

Claims

1. A method for converting an input image in an input color space to an output image in an output color space, wherein said input image comprises a plurality of input pixels;

said method comprises the steps of;

storing, in a first memory, sparsely located output color values of said output color space;

supplying a stream of neighbouring pixels of the input image; and

performing the following steps on each pixel of the stream;

storing, in a cache memory from said first memory, sparsely located output color values corresponding to the input pixels closest to the current input pixel of the stream, if not already present in the cache memory;

retrieving, from said cache memory, sparsely located output color values corresponding to the input pixels closest to the current input pixel of the stream;

interpolating the retrieved output color values to derive an output color value in said output color space.

2. A method as claimed in claim 1, comprising the following step:

generating for each input pixel of the stream, a plurality of memory addresses to the output color values closest to the said input pixel.

3. A method as claimed in claim 2, wherein said generating step comprises the following sub-step:

remapping each said memory address by reordering one or more most significant bits of each memory address.

4. A method as claimed in claim 2 or 3, wherein said generating step comprises the following sub-steps:

retrieving an interval value and a fractional value for each primary color component of the input pixel;

concatenating the interval values of each primary color component of the input pixel;

converting the concatenated interval values into a first address; and

converting said first address into said plurality of said memory addresses.

5. A method as claimed in claim 2, comprising the following further steps:

comparing for each input pixel of the stream, tags of said generated memory addresses with previously stored tags to determine whether the output color values closest to said input pixel are present in said cache memory;

storing, in a tag memory, the tags of said generated memory addresses, when storing in cache memory the output color values closest to the said input pixel.

6. An apparatus for converting an input image in an input color space to an output image in an output color space, wherein said input image comprises a plurality of pixels;

said apparatus comprising;

a first memory for storing sparsely located output color values of said output color space;

means for supplying a stream of neighbouring pixels of the input image;

a cache memory for storing from said first memory, sparsely located output color values corresponding to the input pixels closest to the current input pixel of the stream, if not already present in the cache memory;

retrieval means for retrieving, from said cache memory, sparsely located output color values corresponding to the input pixels closest to the current input pixel of the stream;

interpolation means for interpolating the retrieved output color values to derive an output color value in said output color space.

7. An apparatus as claimed in claim 6, wherein said apparatus comprises:

means for generating, for each input pixel of the stream, a plurality of memory addresses to the output color values closest to the said input pixel.

8. An apparatus as claimed in claim 7, wherein said apparatus comprises:

remapping means for remapping each said memory address by reordering one or more most significant bits of each memory address.

9. An apparatus as claimed in claim 7 or 8, wherein said apparatus comprises:

retrieval means for retrieving an interval value and a fractional value for each primary color component of the input pixel;

concatenating means for concatenating the interval values of each primary color component of the input pixel;

conversion means for converting the concatenated interval values into a first address; and

conversion means for converting said first address into said plurality of said memory addresses.

10. An apparatus as claimed in claim 7 or 8, wherein said apparatus comprises:

comparator means for comparing, for each input pixel of the stream, tags of said generated memory addresses with previously stored tags to determine whether the output color values closest to said input pixel are present in said cache memory;

a tag memory for storing the tags of said generated memory addresses, when storing in cache memory the output color values closest to the said input pixel.