Image processing apparatus

• US 5,748,773 A
• Filed: 11/17/1994
• Issued: 05/05/1998
• Est. Priority Date: 02/21/1992
• Status: Expired due to Term

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Itoh, Akio, Ichikawa, Hiroyuki, Suzuki, Yoshiyuki, Abe, Yoshinori, Tashiro, Hirohiko, Kutsuwada, Satoru
• Primary Examiner(s): Boudreau, Leo
• Assistant Examiner(s): Tran, Phuoc
• Application Number:
  US08/343,885
• Time in Patent Office: 1,265 Days
• Field of Search: 382/168, 382/169, 382/170, 382/171, 382/172, 382/176, 382/254, 382/274, 382/167, 358/519, 358/521, 358/522, 358/548, 358/561, 358/562
• US Class Current: 382/169
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: G06T 5/92 based on global image properties
• CPC Class Codes: H04N 1/4074 using histograms
• CPC Class Codes: H04N 1/4078 using gradational references, e.g. grey-scale test pattern analysis

Abstract

An image processing apparatus having a first mode for processing electrical signals by a pre-scan operation and a second mode for processing electrical signals by a main scan operation. The first mode forms a histogram on the basis of electrical signals obtained by the pre-scan operation, and detects predetermined feature points from the formed histogram. A table is formed for converting signal levels of the electrical signals according to the detected predetermined feature points of the histogram based on the image type of the original. The second mode generates reproduction signals from electrical signals obtained by the main scan operation in accordance with the table.

Claims

1. An image processing apparatus comprising:

first forming means for forming a histogram on the basis of input electrical signals;

detection means for detecting predetermined feature points from the formed histogram;

discrimination means for discriminating an image type of an original represented by the input electrical signals according to the detected predetermined feature points;

second forming means for forming a table for converting signal levels of the electrical signals according to the detected predetermined feature points based on the image type of the original discriminated by said discrimination means; and

selecting means for selecting, from the feature points detected by said detection means, at least one suitable feature point for forming the table in accordance with the image type discriminated by said discrimination means.

2. The apparatus according to claim 1, wherein the table formed by said second forming means is a conversion table including conversion of the electrical signals according to the image type of the original, luminance-density conversion and gradation correction.

3. The apparatus according to claim 1, wherein the predetermined feature points include lightest and darkest levels of the levels of the electrical signals, a maximum frequency of frequencies constituting the histogram, and a level of an electrical signal corresponding to the maximum frequency.

4. An image processing apparatus, which has a first mode for processing electrical signals by a prescan operation and a second mode for processing electrical signals by a main scan operation, comprising:

first forming means for forming a histogram on the basis of electrical signals obtained by the prescan operation;

detection means for detecting predetermined feature points from the formed histogram;

discrimination means for discriminating an image type of an original represented by the input electrical signals according to the detected predetermined feature points;

second forming means for forming a table for converting signal levels of the electrical signals according to the detected predetermined feature points based on the image type of the original discriminated by said discrimination means;

generation means for generating reproduction signals on the basis of electrical signals obtained by the main scan operation in accordance with the table formed by said second forming means; and

selecting means for selecting, from the feature points detected by said detection means, at least one suitable feature point for forming the table in accordance with the image type discriminated by said discrimination means.

5. The apparatus according to claim 4, wherein the table formed by said second forming means is a conversion table including conversion of the electrical signals according to the image type of the original, luminance density conversion and gradation correction.

6. The apparatus according to claim 4, wherein the predetermined feature points include lightest and darkest levels of the levels of the electrical signals, a maximum frequency of frequencies constituting the histogram, and a level of an electrical signal corresponding to the maximum frequency.

7. An image processing apparatus, which has a first mode for processing electrical signals by a prescan operation and a second mode for processing electrical signals by a main scan operation, comprising:

first forming means for forming a histogram on the basis of electrical signals obtained by the prescan operation;

detection means for detecting predetermined feature points from the formed histogram;

discrimination means for discriminating an image type of an original represented by the electrical signals according to the detected predetermined feature points;

second forming means for forming a first table for converting luminance signals of the electrical signals according to the discriminated type of original;

third forming means for forming a second table for performing luminance-density conversion of the electrical signals;

generation means for generating reproduction signals from the electrical signals obtained by the main scan operation according to the formed first and second tables; and

selecting means for selecting, from the feature points detected by said detection means, at least one suitable feature point for forming the first table in accordance with the image type discriminated by said discrimination means.

8. The apparatus according to claim 7, wherein the predetermined feature points include lightest and darkest levels of the levels of the electrical signals, a maximum frequency of frequencies constituting the histogram, a level of an electrical signal corresponding to the maximum frequency, a total number of peaks, levels recognized as peaks, and a continuous amount of frequencies of a period having a largest level width of periods where frequencies exceeding a predetermined value continuously appear.

9. The apparatus according to claim 7, wherein said image processing apparatus is connected to a printing apparatus, and the second table further has a table for performing gradation correction of said printing apparatus.

10. An image processing method comprising the steps of:

forming a histogram on the basis of input electrical signals;

detecting predetermined feature points from the formed histogram;

discriminating an image type of an original represented by the input electrical signals according to the detected predetermined feature points; and

forming a table for converting signal levels of the electrical signals according to the detected predetermined feature points based on the discriminated image type of the original; and

selecting, from the detected feature points, at least one suitable feature point for forming the table in accordance with the discriminated image type.

11. An image processing method, which has a first mode for processing electrical signals by a prescan operation and a second mode for processing electrical signals by a main scan operation, comprising the steps of:

forming a histogram on the basis of electrical signals obtained by the prescan operation;

detecting predetermined feature points from the formed histogram;

discriminating an image type of an original represented by the electrical signals according to the detected predetermined feature points;

forming a table for converting signal levels of the electrical signals according to the detected predetermined feature points based on the discriminated image type of the original;

generating reproduction signals on the basis of electrical signals obtained by the main scan operation in accordance with the formed table; and

selecting, from the detected feature points, at least one suitable feature point for forming the table in accordance with the discriminated image type.

12. An image processing method, which has a first mode for processing electrical signals by a prescan operation and a second mode for processing electrical signals by a main scan operation, comprising the steps of:

forming a histogram on the basis of electrical signals obtained by the prescan operation;

detecting predetermined feature points from the formed histogram;

discriminating an image type of an original represented by the electrical signals according to the detected predetermined feature points;

forming a first table for converting luminance signals of the electrical signals according to the discriminated type of original;

forming a second table for performing luminance-density conversion of the electrical signals;

generating reproduction signals from the electrical signals obtained by the main scan operation according to the formed first and second tables; and

selecting, from the detected feature points, at least one suitable feature point for forming the first table in accordance with the discriminated image type.

13. An image processing apparatus comprising:

first forming means for forming a destiny histogram on the basis of input electrical signals;

first detection means for detecting predetermined feature points from the formed histogram;

discrimination means for discriminating an image type of an original represented by the input electrical signals according to the detected predetermined feature points;

second detection means for detecting an effective range of the density of the input electrical signals according to the detected predetermined feature points;

second forming means for forming a table for converting signal levels of the electrical signals according to the detected predetermined feature points and the effective range of the density based on the image type of the original discriminated by said discrimination means; and

selecting means for selecting, from the feature points detected by said first detection means, at least one suitable feature point for forming the table in accordance with the image type discriminated by said discrimination means.

14. The image processing apparatus according to claim 13, wherein said second forming means forms the table so that a converting curve of the table is substantially linear in the effective range, as an input range, detected by said second detection means.

15. The image processing apparatus according to claim 13, wherein said second detection means detects the entire input range of the density of the input electrical signals as an effective range if said discrimination means discriminates that the image type of the original is a gradation image type.

16. An image processing method comprising the steps of:

forming a density histogram on the basis of input electrical signals;

detecting predetermined feature points from the formed density histogram;

discriminating an image type of an original represented by the input electrical signals according to the detected predetermined feature points;

detecting an effective range of the density of the input electrical signals according to the detected feature points;

forming a table for converting signal levels of the electrical signals according to the detected predetermined feature points and the effective range of the density on the basis of the discriminated image type of the original; and

selecting, from the detected feature points, at least one suitable feature point for forming the table in accordance with the discriminated image type.

17. The image processing method according to claim 16, wherein said table is formed so that a converting curve of said table is substantially linear in the detected effective range as an input range of the density of the input electrical signals.

18. The image processing method according to claim 16, wherein the entire input range is detected as an effective range if the image type of the original is discriminated as a gradation image type.