Method and apparatus for the automatic analysis of density range, color cast, and gradation of image originals on the BaSis of image values transformed from a first color space into a second color space

• US 5,668,890 A
• Filed: 08/19/1996
• Issued: 09/16/1997
• Est. Priority Date: 04/06/1992
• Status: Expired due to Fees

• Current Assignee: Heidelberger Druckmaschinen Ag
• Original Assignee: Linotype-Hell AG (Heidelberger Druckmaschinen Ag)
• Inventors: Winkelman, Kurt-Helfried
• Primary Examiner(s): Mancuso, Joseph
• Assistant Examiner(s): Patel, Jayanti K.
• Application Number:
  US08/699,189
• Time in Patent Office: 393 Days
• Field of Search: 382/162, 382/167, 382/276, 358/518, 358/520, 358/521, 358/522, 345/153, 345/154, 395/131
• US Class Current: 382/167
• CPC Class Codes: H04N 1/4074 using histograms
• CPC Class Codes: H04N 1/60 Colour correction or control H04N1/54 takes precedence
• CPC Class Codes: H04N 1/6027 Correction or control of colour gradation or colour contrast H04N1/6058 takes precedence
• CPC Class Codes: H04N 1/6077 Colour balance, e.g. colour cast correction

Abstract

A method and apparatus for analysis of an image original to be reproduced by evaluating image values (R, G, B) acquired by the point-by-point and line-by-line, trichromatic scanning. The image values of a first color space allocated to the input apparatus are transformed into image values of a second color space that is independent of the first color space. The analysis of the image original for calculating setting values for image processing is implemented on the basis of the transformed image values of the second color space. The master analysis on the basis of the image values is implemented in view of image scope, image gradation and/or color cast.

Claims

1. A method for master analysis of an image original to be reproduced by evaluating image values acquired by point-by-point and line-by-line trichromatic scanning of an image original with an image processing input device, comprising the steps of:

transforming each scanned image value of a first RGB color space allocated to the input device into;

a corresponding image value of a CIEXYZ color value system as a reference color system based on visual properties of the human eye, and then transforming each image value in the CIEXYZ system into a corresponding image value of a device independent second color space that is independent of the first color space, said second color space having an equidistant three-dimensional construction and is in conformity with human sensation, the image values of the second color space including a luminance component and first and second color components; and

carrying out an automatic master analysis of the image original for calculating setting values for the image processing for image scope, image gradation, and color cast on the basis of the transformed image values of the second color space without manual intervention by an operator.

2. The method of claim 1, comprising the steps of:

calculating and identifying a frequency distribution of a luminance component of the transformed image values in the image original; and

calculating a light image value of the image original and a dark image value of the image original from the frequency distribution by defining maximum and minimum luminance values depending on a curve of a frequency distribution of light image and dark image regions in the image original.

3. The method of claim 1, comprising the steps of:

subdividing a value range of a luminance component of the image values into luminance regions;

identifying an affiliation of the image values to said luminance regions;

checking said luminance regions for a potentially existing color cast for each luminance region;

calculating corresponding color cast values for the image values belonging to the individual luminance regions from the color components by averaging; and

identifying an overall color cast value to be utilized for evaluation of a color cast of the image original by combining the color cast values identified for the luminance regions.

4. The method of claim 3, comprising the steps of:

undertaking subdivision into said luminance regions in an image region of highest luminance values and in an image region of lowest luminance values; and

additionally demarcating the highest luminance values image luminance region and the lowest luminance values image luminance region based on chrominance by forming chrominance regions around a gray axis to form analysis regions and utilizing the analysis regions for checking for potentially existing color casts.

5. The method of claim 1, wherein the master analysis of an image original takes place with reference to image values that are acquired by scanning the image original with a resolution that is coarser than a resolution required for the reproduction of the image original.

6. A method according to claim 1 wherein two color components are provided and wherein hue and chroma are directly derived from the two color components.

7. A method according to claim 1 wherein the second color space is a CIELAB color space having color values L*, a*, and b* where L* represents luminance, a* represents said first color component, and b* represents said second color component.

8. An apparatus for master analysis of an image original to be reproduced by evaluating the image values acquired by point-by-point and line-by-line, trichromatic scanning with an input device, comprising:

a color converter connected to the input device for transforming each scanned image value of a first RGB color space allocated to the input device into a corresponding image value of a CIEXYZ color value system as a reference color system based on visual properties of the human eye, and then transforming each image value into the CIEXYZ system into a corresponding image value of a second color space that is independent of the first color space, said second color space having an equidistant three-dimensional construction and in conformity with human sensation, the image values of the second color space including a luminance component and first and second color components;

an image processing unit connected to the color converter and configured for processing the transformed image values;

an operating terminal coupled to both the color converter and the image processing unit;

a communication unit connected to the image processing unit for intermediate storage of processed image values; and

a master analysis unit connected to the image processing unit and to the operating terminal for conducting an automatic master analysis of an image original based on the transformed image values of the second color space for the purpose of calculating setting values for image processing for image scope, image gradation, and color cast without manual intervention by an operator.

9. A method for master analysis of an image original to be reproduced by evaluating image values acquired by point-by-point and line-by-line trichromatic scanning of an image original with an image processing input device, comprising the steps of:

transforming each scanned image value of a first RGB color space allocated to the input device into a corresponding image value of a CIEXYZ color value system as a reference color system based on visual properties of the human eye, and then transforming each image value in the CIEXYZ system into a corresponding image value of a device independent second color space that is independent of the first color space, said second color space having an equidistant three-dimensional construction and is in conformity with human sensation, the image values of the second color space including a luminance component and first and second color components;

calibrating the conversion of image values of the first color space into the image values of the second color space by forming a conversion table from image values of the first color space, taking spectral and electrical properties of the input device into consideration;

opto-electronically scanning a test image original containing a plurality of defined test colors with the input device for acquiring image values of the first color space, the test image original comprising the same material properties as the image original to be scanned later with the input device;

converting the image values of the first color space acquired by scanning the test image original into image values of the second color space with reference of the conversion table;

comparing the image values of the second color space acquired by scanning the test image original to image values of the corresponding test color values colorimetrically measured for a given type of light to acquire color difference values;

calculating correction color values for the image values stored in the conversion table according to said color difference values; and

carrying out an automatic master analysis of the image original for calculating setting values for the image processing for image scope, image gradation, and color cast on the basis of the transformed image values of the second color space without manual intervention by an operator.

10. An apparatus for master analysis of an image original to be reproduced by evaluating the image values acquired by point-by-point and line-by-line, trichromatic scanning with an input device, comprising:

a color converter connected to the input device for transforming each scanned image value of a first RGB color space allocated to the input device into a corresponding image value of a CIEXYZ color value system as a reference color system based on visual properties of the human eye, and then transforming each image value into the CIEXYZ system into a corresponding image value of a second color space that is independent of the first color space, said second color space having an equidistant three-dimensional construction and in conformity with human sensation, the image values of the second color space including a luminance component and first and second color components;

an image processing unit connected to the color converter and configured for processing the transformed image values;

an operating terminal coupled to both the color converter and the image processing unit;

a communication unit connected to the image processing unit for intermediate storage of processed image values; and

a master analysis unit connected to the image processing unit and to the operating terminal for conducting an automatic master analysis of an image original based on the transformed image values of the second color space for the purpose of calculating setting values for image processing for image scope, image gradation, and color cast without manual intervention by an operator.

11. An apparatus according to claim 10 wherein two color components are provided and wherein hue and chroma are directly derived from the two color components.

12. An analysis according to claim 10 wherein the second color space is a CIELAB color space having color values L*, a*, and b* where L* represents luminance, a* represents said first color component, and b* represents said second color component.

13. A method for master analysis of an image original to be reproduced by evaluating image values acquired by point-by-point and line-by-line, trichromatic scanning of an image original with an image processing input device, comprising the steps of:

transforming each scanned image value of a first RGB color space allocated to the input device into a corresponding image value of a CIEXYZ color value system as a reference color system based on visual properties of the human eye, and then transforming each image value in the CIEXYZ system into a corresponding image value of a second color space that is independent of the first color space, the image values of the second color space including a luminance component and first and second color components, the second color space having an equidistant three-dimensional construction in conformity with human sensation; and

carrying out an automatic master analysis of the image original for calculating setting values for the image processing on the basis of the transformed image values of the second color space, said setting values being carried out for image scope, image gradation, and color cast, the analysis for the color cast using the first and second color components, and the analysis for the image scope and the image gradation using the luminance component.