Image processing method, image processing device, and recording medium

• US 6,724,941 B1
• Filed: 09/30/1999
• Issued: 04/20/2004
• Est. Priority Date: 09/30/1998
• Status: Expired due to Term

• Current Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Fuji Photo Film Co Limited (Fujifilm Holdings Corporation)
• Inventors: Aoyama, Tatsuya
• Primary Examiner(s): COUSO, YON JUNG
• Application Number:
  US09/409,665
• Time in Patent Office: 1,664 Days
• Field of Search: 382/254, 382/263, 382/132, 382/260, 382/264, 382/298, 358/447, 358/532, 358/530
• US Class Current: 382/254
• CPC Class Codes: G06T 5/75 Unsharp masking

Abstract

An image processing method includes a step for inputting the type of digital camera used for obtaining an original image signal to be processed, a step for preparing a non-sharp mask signal of the original image signal, a step for reading a contrast table and a density dependent table corresponding to the type of digital camera from a hard disk device, a step for carrying out sharpness enhancement processing based on the contrast table, the density dependent table, the non-sharp mask signal and the original image signal so that the maximum value of responses of the spatial frequency characteristics of an image signal on which the sharpness enhancement processing has been effected is a value in the region of 1.5 to 3.0 times the spatial frequency characteristics of the original image signal. Accordingly, spatial frequency enhancement processing can be carried out under preferred processing conditions on the original image signal obtained by the digital still camera.

Claims

1. An image processing method, wherein a spatial frequency enhancement processing is carried out on an original image signal obtained by photography using a digital still camera in such a manner that a maximum value of responses of the spatial frequency characteristics of an image signal on which the spatial frequency enhancement processing has been effected is a value substantially in the range of 1.5 to 3.0 times a maximum value of responses of the spatial frequency characteristics of the original image signal on which the spatial frequency enhancement processing has not been effected yet, and

wherein the spatial frequency enhancement processing is carried out based on the following expression:

2. The image processing method according to claim 1, wherein the spatial frequency characteristics of the non-sharp mask signal S_us is such that on an image outputted by using an image signal on which the spatial frequency enhancement processing has been effected utilizing the non-sharp mask signal S_us, a response of the spatial frequency of 0 to 0.5 cycle/mm is equal to or less than 1.2 times the response of the image signal on which the spatial frequency enhancement processing has not been effected yet.

3. The image processing method according to claim 1, wherein a magnitude of the function F (S_org−

S_us) is smaller than a magnitude of the contrast value if the magnitude of the contrast value is below a predetermined contrast threshold.

4. The image processing method according to claim 2, wherein a magnitude of the function F (S_org−

S_us) is smaller than a magnitude of the contrast value if the magnitude of the contrast value is below a predetermined contrast threshold.

5. The image processing method according to claim 3, wherein the function F (S_org−

S_us) is 0 when the magnitude of the contrast value is smaller than the predetermined contrast threshold.

6. The image processing method according to claim 4, wherein the function F (S_org−

S_us) is 0 when the magnitude of the contrast value is smaller than a predetermined contrast threshold.

7. The image processing method according to claim 1, wherein a value of the function G (S_org) decreases as a density of the image on which the spatial frequency enhancement processing has not been effected yet increases.

8. The image processing method according to claim 2, wherein a value of the function G (S_org) decreases as a density of the image on which the spatial frequency enhancement processing has not been effected yet increases.

9. An The image processing method according to claim 3, wherein a value of the function G (S_org) decreases as a density of the image on which the spatial frequency enhancement processing has not been effected yet increases.

10. The image processing method according to claim 5, wherein a value of the function G (S_org) decreases as a density of the image on which the spatial frequency enhancement processing has not been effected yet increases.

15. The image processing method according to claim 1, wherein an enhancement is suppressed for image portions whose frequency bands are below a predetermined frequency threshold.

16. The image processing method according to claim 1, wherein an enhancement is suppressed for image portions whose contrasts are below a predetermined contrast threshold.

17. The image processing method according to claim 1, wherein the spatial frequency enhancement processing is carried out based on the following expression:

18. The image processing method according to claim 17, wherein H (ω

₁, ω

₂)=1+c {sin² (ω

₁/2)+sin² (ω

₂/2)} and c is a constant value above 0.

11. An image processing method, wherein an enlargement processing or reduction processing is carried out on an original image signal obtained by photography using a digital still camera, and, in carrying out a spatial frequency enhancement processing, a response of the spatial frequency characteristics of an image signal on which the spatial frequency enhancement processing has been effected is adjusted according to the spatial frequency characteristics of the enlargement processing or the reduction processing, and

wherein the adjustment is such that a maximum value of responses of the spatial frequency characteristics, in which the spatial frequency characteristics of the enlargement processing or the reduction processing and the spatial frequency characteristics of the image signal on which the spatial frequency enhancement processing has been effected are combined, is a value in the range of 1.0 to 2.5 times a maximum value of responses of the spatial frequency characteristics of the original image signal on which the spatial frequency enhancement processing has not been effected yet.

12. An The image processing method according to claim 11, wherein the adjustment is an adjustment in accordance with a scale of enlargement when the enlargement processing is carried out, or with a scale of reduction when the reduction processing is carried out.

13. An image processing device, comprising:

enlargement/reduction means for carrying out enlargement processing or reduction processing on an original image signal obtained by photography using a digital still camera; and

adjusting means for adjusting a response of the spatial frequency characteristics of an image signal on which the spatial frequency enhancement processing has been effected, according to the spatial frequency characteristics of the enlargement processing or the reduction processing,

wherein the adjustment is such that a maximum value of responses of the spatial frequency characteristics, in which the spatial frequency characteristics of the enlargement processing or the reduction processing and the spatial frequency characteristics of the image signal on which the spatial frequency enhancement processing has been effected are combined, is a value in the range of 1.0 to 2.5 times a maximum value of responses of the spatial frequency characteristics of the original image signal on which the spatial frequency enhancement processing has not been effected yet.

14. A recording medium having a program recorded thereon for allowing a computer to execute processing that includes:

a step in which enlargement processing or reduction processing is carried out on an original image signal obtained by photography using a digital still camera; and

a step in which a response of the spatial frequency characteristics of an image signal on which the spatial frequency enhancement processing has been effected is adjusted according to the spatial frequency characteristics of the enlargement processing or the reduction processing,

wherein the adjustment is such that a maximum value of responses of the spatial frequency characteristics, in which the spatial frequency characteristics of the enlargement processing or the reduction processing and the spatial frequency characteristics of the image signal on which the spatial frequency enhancement processing has been effected are combined, is a value in the range of 1.0 to 2.5 times a maximum value of responses of the spatial frequency characteristics of the original image signal on which the spatial frequency enhancement processing has not been effected yet.