Non-phase shifting bidimensional filter

• US 7,152,085 B2
• Filed: 10/18/2002
• Issued: 12/19/2006
• Est. Priority Date: 10/19/2001
• Status: Active Grant

• Current Assignee: Stmicroelectronics France (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SA (STMicroelectronics NV)
• Inventors: Tisse, Christel-Loic
• Primary Examiner(s): Mai, Tan V.
• Application Number:
  US10/273,742
• Publication Number:
  US 20030076161A1
• Time in Patent Office: 1,523 Days
• Field of Search: 708/308
• US Class Current: 708/308
• CPC Class Codes: G06V 10/431 Frequency domain transformation; Autocorrelation
• CPC Class Codes: G06V 40/18 Eye characteristics, e.g. of the iris
• CPC Class Codes: H03H 17/0202 Two or more dimensional filters; Filters for complex signals multidimensional convolutions G06F17/153

Abstract

A band-pass filter with at least one passband, which is real, bidimensional, oriented along the phase axis and resulting from the product of two identical one-dimensional Hamming windows, the transfer function of each of these windows being:

$X_i\left(f\right)={\alpha }_i+\left(1-{\alpha }_i\right)\cos \frac{\pi \left(f-f{q}_i\right)}{{\mathrm{f0}}_i},where$

• • f is a current frequency;
  • αi is a real number, included between and excluding 0 and 1;
  • fqi is a central frequency of the passband; and
  • f0i defines half of the passband centered on fqi.

Claims

1. A band-pass filter in the frequency domain with at least one pass band, which is real, bidimensional, oriented along a phase axis and resulting from the product of two identical one-dimensional Hamming windows, a transfer function of each of these windows being:

$X_i<br><br>\left(f\right)={\mathrm{\alpha <br><br>}}_i+\left(1-{\mathrm{\alpha <br><br>}}_i\right)<br><br>\cos <br><br>\frac{\mathrm{\pi <br><br>}<br><br>\left(f-f<br><br><br><br>q_i\right)}{{\mathrm{f0}}_i},$

where;

f is a current frequency;

α

_i is a real number, included between and excluding 0 and 1;

fq_i is a central frequency of the passband; and

f0_i defines half of the passband centered on fq_i.

2. The filter of claim 1, wherein the windows are Hanning windows, for which a real number α

_i is 0.54.

3. The filter of claim 1, wherein the filter has a passband having a width of one octave.

4. The filter of claim 3, wherein the windows are Hanning windows and wherein the passband of each of the Hanning windows is defined by:

${\mathrm{f0}}_i=\frac{\mathrm{\pi <br><br>}}{3<br><br>\mathrm{arcos}\left(\frac{\frac{1}{2}-{\mathrm{\alpha <br><br>}}_i}{1-{\mathrm{\alpha <br><br>}}_i}\right)}<br><br>f<br><br><br><br>q_i,$

where arcos designates the inverse cosine function.

5. A band-pass filter with several passbands, wherein each passband is defined by claim 1.

6. The filter of claim 1, wherein such a filter is applied to a detection of a texture of a ring-shaped element, the texture being a set of information varying according to an angular position in concentric circles.

7. The filter of claim 1, wherein the filter is used to process a digital image.