Arbitrary power function using logarithm lookup table

• US 20080180576A1
• Filed: 01/25/2007
• Published: 07/31/2008
• Est. Priority Date: 01/25/2007
• Status: Active Grant

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm MEMS Technologies Incorporated (Qualcomm, Inc.)
• Inventors: Anderson, Michael H.
• Granted Patent: US 7,957,589 B2
• Time in Patent Office: Days
• US Class Current: 348/674
• 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 lookup table; and

a processing circuit configured to provide both forward lookups and reverse lookups during a gamma translation process.

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 wherein said lookup table comprises a set of logarithms associated with a set of values.

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

6. The image-processing device of claim 1 wherein said processing circuit is configured to search a set of logarithms for an index associated with a value.

7. An image display device comprising:

a stored gamma value; and

a forward logarithm lookup table and a inverse logarithm lookup table.

8. The image display device of claim 7 wherein said forward logarithm lookup table is said inverse logarithm lookup table.

9. The image display device of claim 7 further comprising a multiplier.

10. The image display device of claim 7 further comprising a monitor.

11. The image display device of claim 7 further comprising a video card.

12. The image display device of claim 7 further comprising circuitry configured to transform image data with respect to said stored gamma value and to display a transformed image.

13. A method comprising:

obtaining a numerical representation of a color intensity level;

looking up a logarithm value associated with at least one element of said numerical representation of a color intensity level in a lookup table;

storing a result of said looking up;

multiplying said result of looking up by a fractional portion of a gamma translation value and storing said result as an exponent value;

using said lookup table in reverse to obtain the inverse logarithm of said exponent value; and

multiplying said inverse logarithm of said exponent value by said element of said numerical representation of a color intensity level raised to a power defined by an integer portion of said gamma translation value.

14. The method of claim 13 wherein said numerical representation of a color intensity level is an RGB value.

15. The method of claim 13 wherein said numerical representation of a color intensity level is an CMYK value.

16. The method of claim 13 wherein said gamma translation value is a positive non-integer.

17. The method of claim 13 wherein said lookup table is a logarithm lookup table.

18. A method comprising:

storing a color value in a computer-readable memory;

storing a desired gamma translation value in a computer-readable memory;

separating said gamma translation value into a non-integer part and an integer part;

looking up the logarithm of said color value and storing said logarithm of said color value as a forward log value;

multiplying said non-integer part by said forward log value and storing a result of said multiplying as an exponent value;

determining the inverse logarithm of said exponent value and storing said inverse logarithm of said exponent value as an inverse logarithm result;

raising said color value to a power defined by said integer part and storing a result of said raising as a raising result; and

multiplying said inverse logarithm result and said raising result to produce a transformed color value.

19. A method comprising:

multiplying a fractional portion of a gamma value by the logarithm of a color value to obtain an exponent value;

finding the inverse logarithm of said exponent value; and

obtaining a gamma-transformed color value using said inverse logarithm.

20. An apparatus comprising:

a display;

a stored non-integer gamma value; and

means for exponentiating numerical color values by said non-integer gamma value, said means comprising;

means for performing forward logarithm lookups; and

means for performing inverse logarithm lookups.

21. The apparatus of claim 20, wherein at least a portion of the structure of said means for performing forward logarithm lookups is common to said means for performing inverse logarithm lookups.

22. A processing device comprising:

a lookup table; and

a processing circuit configured to provide both forward lookups and reverse lookups during a process of calculating a non-integer power of a number.