US4731671A
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Contrast adjustment in digital image processing method employing histogram normalization
Assignee: Eastman Kodak Co
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Filing: 1985-05-06
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Granted: 1988-03-15
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Expires: 2005-05-06
Abstract
Abstract A problem in digital image processing employing a tone reproduction function that maximizes the quality of the processed image is to automatically determine the overall contrast of the processed image. In an improved method for determining the contrast of the processed image, the contrast is automatically determined as a function of the standard deviation of a sample of tone values used to generate the tone reproduction function by normalizing a histogram of the sample of tone values. The sample of tone values is selected from one of a plurality of samples of tone values corresponding to a plurality of contrast intervals based upon the shape of the histogram of the selected sample of tone values. To facilitate the adjustment of contrast, the tone reproduction function is constructed to produce values in units of a standard normal variate Z. These Z values are then multiplied by a constant which is a function of the standard deviation of the sample of tone values to determine the contrast of the processed image. A constant representing the mean density of the output medium is added to the multiplied Z values to position the tone scale of the processed image with respect to the tonal range of the output medium.
Inventors
- 👤 James S. Alkofer
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 07:56
CPC Classifications
H; H04; H04N; H04N1/00; H04N1/40; H04N1/407; H04N1/4072; H04N1/4074
Claims Analysis
Total Claims: 20
Claim 1
Independent Claim
70 words
A digital image processing method employing a tone reproduction function generated by normalizing a histogram of a sample of tone values selected from informational portions of a digital image to produce a processed digital image having improved contrast characterized by the steps of computing the standard deviation of the sample of tone values, and of adjusting the contrast of the processed digital image as a function of the standard deviation.
Claim 2
Dependent Claim
70 words
A digital image processing method employing a tone reproduction function generated by normalizing a histogram of a sample of tone values selected from informational portions of a digital image to produce a processed digital image having improved contrast characterized by the steps of computing the standard deviation of the sample of tone values, and of adjusting the contrast of the processed digital image as a function of the standard deviation.
Claim 3
Dependent Claim
77 words
The digital image processing method claimed in claim 1, wherein the tone reproduction function relates tone values to Z values (i.e. values of a standard normal variate Z), the tone reproduction function being applied to tone values of the digital image to produce processed Z values, and said step of adjusting contrast comprises multiplying said processed Z values by a contrast adjusting constant which is a function of the standard deviation of the sample of tone values.
Claim 4
Dependent Claim
60 words
The digital image processing method claim ed in claim 2, wherein said digital image is to be displayed on an output medium with a desired mean density, said method further including the step of adding a constant representing the desiring mean density of the output medium to said processed Z values which have been multiplied by said contrast adjusting constant.
Claim 5
Dependent Claim
56 words
The digital image processing method claimed in claim 2, wherein said function of the standard deviation of the sample of tone values is of the form σ.sub.z =m·σ.sub.s +b where: σ z is the contrast adjusting contant, σ s is the standard deviation of the sample of tone values, and m and b are system-dependent constants.
Claim 6
Dependent Claim
47 words
The digital image processing method claimed in claim 2, wherein said sample of tone values is selected from a plurality of samples of tone values corresponding to a plurality of contrast intervals on the basis of statistics of the distributions of the tone values in the samples.
Claim 7
Dependent Claim
26 words
The digital image processing method claimed in claim 5, wherein the sample of tone values having the most nearly normal distribution of tone values is selected.
Claim 8
Dependent Claim
135 words
A digital image processing apparatus for processing tone values of a digital image to produce a processed digital image, comprising: means for selecting a sample of tone values from informational portions of the digital image; means for normalizing the sample of tone values to produce a tone reproduction function, the tone reproduction function relating tone values to values of a standard normal variate Z (Z values); means for applying the tone reproduction function to tone values of the digital image to produce processed Z values; means for computing the standard deviation of the sample of tone values; and means for adjusting the contrast of the processed digital image comprising means for multiplying said processed Z values by a contrast adjusting constant which is a function of the standard deviation of the sample of tone values.
Claim 9
Dependent Claim
135 words
A digital image processing apparatus for processing tone values of a digital image to produce a processed digital image, comprising: means for selecting a sample of tone values from informational portions of the digital image; means for normalizing the sample of tone values to produce a tone reproduction function, the tone reproduction function relating tone values to values of a standard normal variate Z (Z values); means for applying the tone reproduction function to tone values of the digital image to produce processed Z values; means for computing the standard deviation of the sample of tone values; and means for adjusting the contrast of the processed digital image comprising means for multiplying said processed Z values by a contrast adjusting constant which is a function of the standard deviation of the sample of tone values.
Claim 10
Dependent Claim
55 words
The digital image processing apparatus claimed in claim 7, including means for displaying the processed digital image on an output medium with a desired mean density, and means for adding a constant representing the desired mean density of the output medium to the processed Z values which have been multiplied by said contrast adjusting constant.
Claim 11
Dependent Claim
56 words
The digital image processing apparatus claimed in claim 8, wherein said function of the standard deviation of the sample of tone values is of the form σ.sub.z =m·σ.sub.s +b where: σ z is the contrast adjusting constant; σ s is the standard deviation of the sample of tone values, and m and b are system-dependent constants.
Claim 12
Dependent Claim
78 words
The digital image processing apparatus claimed in claim 8, wherein said means for selecting a sample of tone values includes means for forming a plurality of histograms of tone values from a corresponding plurality of samples of tone values corresponding to a plurality of contrast intervals, and means for selecting one of the samples of tone values corresponding to one of the contrast intervals on the basis of statistics of the histograms of the samples of tone values.
Claim 13
Dependent Claim
23 words
The digital image processing apparatus claimed in claim 10, wherein the sample of tone values having the most nearly normal histogram is selected.
Claim 14
Dependent Claim
151 words
A digital image processing method of the type employing a tone reproduction function generated by normalizing a sample of tone values from informational portions of a digital image to produce a processed digital image having improved contrast, said processed digital image to be displayed on an output medium with a desired mean density, characterized by: the tone reproduction function being applied to tone values in the digital image to produce values of a standard normal variate Z (Z values) in the processed digital image, and the method including the steps of: computing the standard deviation of the sample of tone values; adjusting the contrast of the processed digital image by multiplying the Z values by a contrast adjusting constant which is a function of the standard deviation of the sample of tone values, and adding a constant representing the desired mean density of the output medium to the multiplied Z values.
Claim 15
Dependent Claim
151 words
A digital image processing method of the type employing a tone reproduction function generated by normalizing a sample of tone values from informational portions of a digital image to produce a processed digital image having improved contrast, said processed digital image to be displayed on an output medium with a desired mean density, characterized by: the tone reproduction function being applied to tone values in the digital image to produce values of a standard normal variate Z (Z values) in the processed digital image, and the method including the steps of: computing the standard deviation of the sample of tone values; adjusting the contrast of the processed digital image by multiplying the Z values by a contrast adjusting constant which is a function of the standard deviation of the sample of tone values, and adding a constant representing the desired mean density of the output medium to the multiplied Z values.
Claim 16
Dependent Claim
218 words
A digital image processing method of the type employing a tone reproduction functional generated by normalizing a sample of tone values from informational portions of a digital image to produce a processed digital image having improved contrast, said processed digital image to be displayed on an output medium with a desired means density, characterized by: the sample of tone values being selected from a plurality of samples of tone values corresponding to a plurality of contrast intervals on the basis of statistics of the distributions of the tone values in the samples, and the tone reproduction function being applied to tone values in the digital image to produce values of a standard normal variate Z (Z values) in the processed digital image, and the method including the steps of adjusting the contrast of the processed digital image by multiplying the Z values by a contrast adjusting constant which is a function of the standard deviation of the sample of tone values, the function having the form σ.sub.z =m·σ.sub.s +b where: σ z is the contrast adjusting constant, σ s is the standard deviation of the sample of tone values, and m and b are system-dependent constants; and including the step of adding a constant representing the desired mean density of the output medium to the multiplied Z values.
Claim 17
Dependent Claim
218 words
A digital image processing method of the type employing a tone reproduction functional generated by normalizing a sample of tone values from informational portions of a digital image to produce a processed digital image having improved contrast, said processed digital image to be displayed on an output medium with a desired means density, characterized by: the sample of tone values being selected from a plurality of samples of tone values corresponding to a plurality of contrast intervals on the basis of statistics of the distributions of the tone values in the samples, and the tone reproduction function being applied to tone values in the digital image to produce values of a standard normal variate Z (Z values) in the processed digital image, and the method including the steps of adjusting the contrast of the processed digital image by multiplying the Z values by a contrast adjusting constant which is a function of the standard deviation of the sample of tone values, the function having the form σ.sub.z =m·σ.sub.s +b where: σ z is the contrast adjusting constant, σ s is the standard deviation of the sample of tone values, and m and b are system-dependent constants; and including the step of adding a constant representing the desired mean density of the output medium to the multiplied Z values.
Claim 18
Dependent Claim
59 words
A digital image processing method of the type employing a tone reproduction function generated by normalizing a sample of tone values from informational portions of a digital image, characterized by: the tone reproduction function being applied to tone values in the digital image to produce values of a standard normal variate Z (Z values) in a processed digital image.
Claim 19
Dependent Claim
59 words
A digital image processing method of the type employing a tone reproduction function generated by normalizing a sample of tone values from informational portions of a digital image, characterized by: the tone reproduction function being applied to tone values in the digital image to produce values of a standard normal variate Z (Z values) in a processed digital image.
Claim 20
Dependent Claim
62 words
The digital image processing method claimed in claim 14, including the steps of: computing the standard deviation of the sample of tone values; multiplying the Z values by a constant which is a function of the standard deviation of the sample of tone values; and adding a constant representing a desired mean density of an output medium to the multiplied Z values.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1991-03-15 | 1991-09-14 | 1992-03-15 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1995-03-15 | 1995-09-14 | 1996-03-15 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1999-03-15 | 1999-09-14 | 2000-03-15 | $7700.00 | Window Closed / Lapsed |