Arbitrary power function using logarithm lookup table

• US 7,957,589 B2
• Filed: 01/25/2007
• Issued: 06/07/2011
• Est. Priority Date: 01/25/2007
• Status: Expired due to Fees

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm MEMS Technologies Incorporated (Qualcomm, Inc.)
• Inventors: Anderson, Michael H.
• Primary Examiner(s): Bhatnagar; Anand
• Assistant Examiner(s): CHU, RANDOLPH I
• Application Number:
  US11/698,609
• Publication Number:
  US 20080180576A1
• Time in Patent Office: 1,594 Days
• Field of Search: None
• US Class Current: 382/167
• CPC Class Codes: H04N 5/202 Gamma control circuits for controlling camera response irrespective of the scene brightness H04N23/82

Abstract

A display device performs the fractional part of gamma translation by using a logarithm lookup table. The logarithm of an image data value is found in a look-up table. The retrieved result is multiplied by the fractional portion of the power, and a search in the look up table for this product produces an index related to the desired result. In another embodiment, rather than a search of the first look up table, a second inverse logarithm look up table is used to produce the desired result by looking up the exponentiation of the product.

Claims

1. An image-processing device comprising:

a storage element storing data comprising a lookup table, the lookup table comprising a set of indices and logarithm data related to each index; and

a processing circuit for performing a gamma translation process, wherein the processing circuit is configured to retrieve, from the lookup table, logarithm data based on a provided index and to retrieve an index, from the lookup table, based on a provided logarithm data,

wherein the processing circuit is configured to;

(a) determine the logarithm of a numerical color value by retrieving logarithm data from the lookup table using the color value as the index;

(b) multiply the logarithm of the color value by a fractional portion of a gamma value, thus generating a first value; and

(c) determine the inverse logarithm of the first value by searching the lookup table for logarithm data close to the first value and returning the index linking to the logarithm data as the inverse logarithm of the first value.

2. The image-processing device of claim 1 wherein said processing circuit is configured to translate a value with respect to a non-integer gamma.

3. The image-processing device of claim 1 further comprising a multiplier.

4. The image-processing device of claim 1 further comprising a gamma-adjustment user interface.

5. The image-processing device of claim 1 wherein said processing circuit is configured to search the lookup table for logarithm data close to a provided logarithm data and to return the index linking to the logarithm data.

9. The device of claim 1, wherein the processing circuit is configured to translate a color value with regard to a non-integer gamma value.

10. The device of claim 1, further comprising circuitry configured to transform image data with respect to a gamma value and to display a transformed image.

11. The device of claim 1, further comprising a monitor.

12. The device of claim 1, further comprising a video card.

13. The device of claim 1, wherein said numerical color value represents a color intensity level.

14. The device of claim 1, wherein the color value is an RGB value.

15. The device of claim 1, wherein the color value is an CMYK value.

16. The device of claim 1, wherein said gamma translation value is a positive non-integer.

17. The device of claim 1, wherein said lookup table is a natural logarithm lookup table.

6. An apparatus comprising:

a display;

means for storing a non-integer gamma value; and

means for raising a numerical color value to a power of said non-integer gamma value, said raising means comprising;

means for retrieving logarithm data from a lookup table based on a provided index, the lookup table comprising a set of indices and logarithm data related to each index; and

means for retrieving from the lookup table an index based on a provided logarithm data,

wherein the non-integer gamma value includes an integer portion and a fractional portion, wherein the raising means further comprises;

(a) means for determining the logarithm of the numerical color value by retrieving logarithm data from the lookup table using the numerical color value as the index;

(b) means for multiplying the logarithm of the numerical color value by the fractional portion of the non-integer gamme value, thus generating a first value; and

(c) means for determining the inverse logarithm of the first value by searching the lookup table for logarithm data close to the first value and returning the index linking to the logarithm data as the inverse logarithm of the first value.

18. The apparatus of claim 6, wherein the raising means further comprises:

(d) means for raising the numerical color value to a power defined by the integer portion of the non-integer gamma value and storing the result of said raising as a second value; and

(e) means for multiplying the second value by said inverse logarithm of the first value to produce a third value, the third value being the result of raising the numerical color value to a power of the non-integer gamma value.

19. The apparatus of claim 6, wherein the raising means comprises at least one computing device.

7. A processing device comprising:

a storage element for storing data comprising a lookup table, the lookup table comprising a set of indices and logarithm data relate to each index; and

a processing circuit for raising a base value D to a power of a non-integer power value P, the processing circuit is configured to retrieve, from the lookup table, logarithm data based on a provided index and an index based on a provided logarithm data,

wherein the non-integer power P includes an integer portion and a fractional portion, wherein the processing circuit is configured to;

(a) determine the logarithm of the base value D by retrieving logarithm data from the lookup table using the base value as the index;

(b) multiply the logarithm of the base value by the fractional portion of the non-integer power P, thus generating a first value; and

(c) determine the inverse logarithm of the first value by searching the lookup table for logarithm data close to the first value and returning the index linking to the logarithm data as the inverse logarithm of the first value.

8. The device of claim 7, wherein the processing circuit is further configured to:

(d) raise the base value D to a power defined by the integer portion of the non-integer power P and storing the result of said raising as a second value; and

(e) multiply the second value by said inverse logarithm of the first value to produce a third value, the third value being the result of raising the base value D to a power of the power value P.