EP0335419A2
Expired / Lapsed
EP
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Method of and apparatus for establishing highlight and shadow densities
Assignee: Dainippon Screen Manufacturing Co Ltd
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Filing: 1989-03-31
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Granted: —
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Expires: 2009-03-31
Abstract
Abstract Highlight density (X H ) (or shadow density) is established on the basis of a cumulative histogram (H(X)) of density in an original: First, reference densities (X HR , X HL and X H1 - X Hn ) associated with prescribed reference statistic values (Y HR , Y HL and Y H1 - Y Hn ), respectively, and threshold values (W H1 - W Hn ) are computed. Then, the reference density (X HR ) is compared with a prescribed threshold density (X HS ), and a difference (ΔX Hi ) concerning the reference density (X Hi ) is compared with the threshold value (W Hi ) in a procedure, to thereby select one of procedures for establishing the highlight density.
Inventors
- 👤 Akihiro Dainippon Screen Mfg. Co. Ltd. Nomura
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-10 00:45
CPC Classifications
H; H04; H04N; H04N1/00; H04N1/40; H04N1/407; H04N1/4072; H04N1/4074
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
393 words
A method of establishing a gradation control density X c employed as a highlight density or a shadow density on a gradation correction curve F(X) which is used in gradation correction of image data expressing density of each pixel in an image, said method comprising the steps of: (1) on the basis of said image data, generating a statistical curve Y = S(X) expressing a cumulative density distribution on said image, where said statistical curve Y = S(X) is defined on a X - Y coordinate plane having a X-axis representing density levels and a Y-axis representing a cumulative number of pixels in an arbitrary scale, (2) providing a threshold density X TH on said X-axis, (3) finding a terminal value Y m on said Y-axis at which said statistical curve Y = S(X) is terminated, (4) providing a first reference value Y 1R on said Y-axis, (5) finding a terminal density X m on said X-axis at which said statistical curve Y = S(X) reaches said terminal value Y m , (6) converting said first reference value Y 1R through said statistical curve Y = S(X), to thereby obtain a first reference density X 1R , (7) comparing said first reference density X 1R with said threshold density X TH , to thereby designate said statistical curve Y = S(X) as a first type corresponding to an extraordinarily-bright image or an extraordinarily-dark image when said first reference density X 1R is farther from said terminal density X m than said threshold density X TH is, or as a second type corresponding to an ordinary image other than said extraordinarily-bright image and said extraordinarily-dark image when said first reference density X 1R is closer to said terminal density X m than said threshold density X TH is, (8) selecting a first procedure for setting said gradation control density X c at a terminal reference density X TR predetermined between said terminal density X m and said first reference density X 1R when said statistical curve Y = S(X) is said first ype, or selecting a second procedure other than said first procedure for setting said gradation control density X c when said statistical curve Y = S(X) is said second type, and (9) establishing said gradation control density X c through said first procedure or said second procedure selected at said step (8).
Claim 2
Independent Claim
393 words
A method of establishing a gradation control density X c employed as a highlight density or a shadow density on a gradation correction curve F(X) which is used in gradation correction of image data expressing density of each pixel in an image, said method comprising the steps of: (1) on the basis of said image data, generating a statistical curve Y = S(X) expressing a cumulative density distribution on said image, where said statistical curve Y = S(X) is defined on a X - Y coordinate plane having a X-axis representing density levels and a Y-axis representing a cumulative number of pixels in an arbitrary scale, (2) providing a threshold density X TH on said X-axis, (3) finding a terminal value Y m on said Y-axis at which said statistical curve Y = S(X) is terminated, (4) providing a first reference value Y 1R on said Y-axis, (5) finding a terminal density X m on said X-axis at which said statistical curve Y = S(X) reaches said terminal value Y m , (6) converting said first reference value Y 1R through said statistical curve Y = S(X), to thereby obtain a first reference density X 1R , (7) comparing said first reference density X 1R with said threshold density X TH , to thereby designate said statistical curve Y = S(X) as a first type corresponding to an extraordinarily-bright image or an extraordinarily-dark image when said first reference density X 1R is farther from said terminal density X m than said threshold density X TH is, or as a second type corresponding to an ordinary image other than said extraordinarily-bright image and said extraordinarily-dark image when said first reference density X 1R is closer to said terminal density X m than said threshold density X TH is, (8) selecting a first procedure for setting said gradation control density X c at a terminal reference density X TR predetermined between said terminal density X m and said first reference density X 1R when said statistical curve Y = S(X) is said first ype, or selecting a second procedure other than said first procedure for setting said gradation control density X c when said statistical curve Y = S(X) is said second type, and (9) establishing said gradation control density X c through said first procedure or said second procedure selected at said step (8).
Claim 3
Dependent Claim
54 words
A method in accordance with claim 1, wherein said terminal reference density X TR is computed by converting a terminal reference value Y TR through said statistical curve Y = S(X), where said terminal reference value Y TR is preset between said terminal value Y m and said first reference value Y 1R .
Claim 4
Dependent Claim
120 words
A method in accordance with claim 2, wherein said second procedure comprises the steps of (a) presetting a first difference D between said gradation control density X c and a terminal density X a of said gradation correction curve F(X), (b) substantially finding a line approximate to an end portion of said statistical curve Y = S(X), (c) computing a terminal density X im of said line at which said line reaches said terminal value Y m , and (d) establishing said gradation control density X c so that said first difference D agrees within a prescribed error with a second difference D i between said gradation control density X c and said terminal density X im of said line.
Claim 5
Dependent Claim
140 words
A method in accordance with claim 3, wherein said line is a straight line drawn through a first point P₀ and a second point P i , where said first point P₀ is specified by a combination of a prescribed second reference value Y 2R on said Y-axis and a second reference density X 2R computed by converting said second reference value Y 2R through said statistical curve Y = S(X) and said second point P i is specified by a combination of a prescribed third reference value Y i on said Y-axis and a third reference density X i computed by converting said third reference value Y i through said statistical curve Y = S(X), while said third reference value Y i is preset farther from said terminal value Y m than said second reference value Y 2R is.
Claim 6
Dependent Claim
133 words
A method in accordance with claim 4, wherein said third reference value Y i and said third reference density X i include a plurality of candidate values Y₁ -Y n and a plurality of candidate densities X₁ - X n , respectively, said plurality of candidate values Y₁ - Y n are sequentially selected one by one in descent order of differences between said candidate values Y₁ - Y n and said terminal value Y m to specify said second point P i , and a candidate density which is obtained by converting a selected candidate value through said statistical curve Y = S(X) is designated as said gradation control density X c under the condition that said first difference D agrees within said prescribed error with said second difference D i .
Claim 7
Independent Claim
231 words
A method of establishing a gradation control density X c employed as a highlight density or a shadow density on a gradation correction curve F(X) which is used in gradation correction of image data expressing density of each pixel in an image, said method comprising the steps of: (a) on the basis of said image data, generating a statistical curve Y = S(X) expressing a cumulative density distribution on said image, where said statistical curve Y = S(X) is defined on a X - Y coordinate plane having a X-axis representing density levels and a Y-axis representing a cumulative number of pixels in an arbitrary scale, (b) substantially finding a line approximate to an end portion of said statistical curve Y = S(X), (c) presetting a first difference D between said gradation control density X c and a terminal density X a of said gradation correction curve F(X), (d) finding a terminal value Y m on said Y-axis at which said statistical curve Y = S(X) is terminated, (d) computing a terminal density X im of said line at which said line reaches said terminal value Y m , and (f) establishing said gradation control density X c so that said first difference D agrees within a prescribed error with a second difference D i between said gradation control density X c and said terminal density X im of said line.
Claim 8
Independent Claim
231 words
A method of establishing a gradation control density X c employed as a highlight density or a shadow density on a gradation correction curve F(X) which is used in gradation correction of image data expressing density of each pixel in an image, said method comprising the steps of: (a) on the basis of said image data, generating a statistical curve Y = S(X) expressing a cumulative density distribution on said image, where said statistical curve Y = S(X) is defined on a X - Y coordinate plane having a X-axis representing density levels and a Y-axis representing a cumulative number of pixels in an arbitrary scale, (b) substantially finding a line approximate to an end portion of said statistical curve Y = S(X), (c) presetting a first difference D between said gradation control density X c and a terminal density X a of said gradation correction curve F(X), (d) finding a terminal value Y m on said Y-axis at which said statistical curve Y = S(X) is terminated, (d) computing a terminal density X im of said line at which said line reaches said terminal value Y m , and (f) establishing said gradation control density X c so that said first difference D agrees within a prescribed error with a second difference D i between said gradation control density X c and said terminal density X im of said line.
Claim 9
Dependent Claim
140 words
A method in accordance with claim 6, wherein said line is a straight line drawn through a first point P₀ and a second point P i , where said first point P₀ is specified by a combination of a prescribed first reference value Y 2R on said Y-axis and a first reference density X 2R computed by converting said first reference value Y 2R through said statistical curve Y = S(X) and said second point P i is specified by a combination of a prescribed second reference value Y i on said Y-axis and a second reference density X i computed by converting said second reference value Y i through said statistical curve Y = S(X), while said second reference value Y i is preset farther from said terminal value Y m than said first reference value Y 2R is.
Claim 10
Dependent Claim
134 words
A method in accordance with claim 7, wherein said second reference value Y i and said second reference density X i include a plurality of candidate values Y₁ - Y n and a plurality of candidate densities X₁ - X n , respectively, said plurality of candidate values Y₁ - Y n are sequentially selected one by one in descent order of differences between said candidate values Y₁ - Y n and said terminal value Y m to specify said second point P i , and a candidate density which is obtained by converting a selected candidate value through said statistical curve Y = S(X) is designated as said gradation control density X c under the condition that said first difference D agrees within said prescribed error with said second difference D i .
Claim 11
Independent Claim
354 words
An apparatus for establishing a gradation control density X c employed as a highlight density or a shadow density on a gradation correction curve F(X) which is used in gradation correction of image data expressing density of each pixel in an image, said apparatus comprising: (1) a first processor means for generating a statistical curve Y = S(X) expressing a cumulative density distribution on said image on the basis of said image data, where said statistical curve Y = S(X) is defined on a X-Y coordinate plane having a X-axis representing density levels and a Y-axis representing a cumulative number of pixels in an arbitrary scale, (2) a second processor means for finding a terminal density X m on said X-axis at which said statistical curve Y = S(X) is temrinated, (3) a third processor means for computing a first reference density X 1R by converting a prescribed first reference value Y 1R on said Y-axis through said statistical curve Y = S(X), (4) a fourth processor means for comparing said first reference density X 1R with a prescribed threshold density X TH , to thereby designate said statistical curve Y = S(X) as a first type corresponding to an extraordinarily-bright image or an extraordinarily-dark image when said first reference density X 1R is farther from said terminal density X m than said threshold density X TH is, or as a second type corresponding to an ordinary image other than said extraordinarily-bright image and said extraordinarily-dark image when said first reference density X 1R is closer to said terminal density X m than said threshold density X TH is, (5) a fourth processor for establishing said gradation control density X c through a first procedure for setting said gradation control density X c at a terminal reference density X TR predetermined between said terminal density X m and said first reference density X 1R when said statistical curve Y = S(X) is said first type, or through a second procedure other than said first procedure for setting said gradation control density X c when said statistical curve Y = S(X) is said second type.
Claim 12
Independent Claim
354 words
An apparatus for establishing a gradation control density X c employed as a highlight density or a shadow density on a gradation correction curve F(X) which is used in gradation correction of image data expressing density of each pixel in an image, said apparatus comprising: (1) a first processor means for generating a statistical curve Y = S(X) expressing a cumulative density distribution on said image on the basis of said image data, where said statistical curve Y = S(X) is defined on a X-Y coordinate plane having a X-axis representing density levels and a Y-axis representing a cumulative number of pixels in an arbitrary scale, (2) a second processor means for finding a terminal density X m on said X-axis at which said statistical curve Y = S(X) is temrinated, (3) a third processor means for computing a first reference density X 1R by converting a prescribed first reference value Y 1R on said Y-axis through said statistical curve Y = S(X), (4) a fourth processor means for comparing said first reference density X 1R with a prescribed threshold density X TH , to thereby designate said statistical curve Y = S(X) as a first type corresponding to an extraordinarily-bright image or an extraordinarily-dark image when said first reference density X 1R is farther from said terminal density X m than said threshold density X TH is, or as a second type corresponding to an ordinary image other than said extraordinarily-bright image and said extraordinarily-dark image when said first reference density X 1R is closer to said terminal density X m than said threshold density X TH is, (5) a fourth processor for establishing said gradation control density X c through a first procedure for setting said gradation control density X c at a terminal reference density X TR predetermined between said terminal density X m and said first reference density X 1R when said statistical curve Y = S(X) is said first type, or through a second procedure other than said first procedure for setting said gradation control density X c when said statistical curve Y = S(X) is said second type.
Claim 13
Dependent Claim
133 words
An apparatus in accordance with claim 9, wherein said fourth processor means further comprises sub- processor means for executing said second procedure, said sub-processor means including: (a) a first sub-processor means for substantially finding a line approximate to an end portion of said statistical curve Y = S(X), (b) a second sub-processor means for computing a terminal density X im at which said line is terminated, and (c) a third sub-processor means for establishing said gradation control density X c so that a prescribed first difference D between said gradation control density X c and a terminal density X a of said gradation correction curve F(X) agrees within a prescribed error with a second difference D i between said gradation control density X c and said terminal density X im of said line.
Claim 14
Independent Claim
213 words
An apparatus for establishing a gradation control density X c employed as a highlight density or a shadow density on a gradation correction curve F(X) which is used in gradation correction of image data expressing density of each pixel in an image, said apparatus comprising: (1) a first processor means for generating a statistical curve Y = S(X) expressing a cumulative density distribution on said image on the basis of said image data, where said statistical curve Y = S(X) is defined on a X-Y coordinate plane having a X-axis representing density levels and a Y-axis representing a cumulative member of pixels in an arbitrary scale, (2) a second processor means for substantially finding a line approximate to an end portion of said statistical curve Y = S(X), (3) a third processor means for computing a terminal density X im at which said line is terminated, and (4) a fourth processor means for establishing said gradation control density X c so that a prescribed first difference D between said gradation control density X c and a terminal density X a of said gradation correction curve F(X) agrees within a prescribed error with a second difference D i between said gradation control density X c and said terminal density X im of said line.
Claim 15
Independent Claim
213 words
An apparatus for establishing a gradation control density X c employed as a highlight density or a shadow density on a gradation correction curve F(X) which is used in gradation correction of image data expressing density of each pixel in an image, said apparatus comprising: (1) a first processor means for generating a statistical curve Y = S(X) expressing a cumulative density distribution on said image on the basis of said image data, where said statistical curve Y = S(X) is defined on a X-Y coordinate plane having a X-axis representing density levels and a Y-axis representing a cumulative member of pixels in an arbitrary scale, (2) a second processor means for substantially finding a line approximate to an end portion of said statistical curve Y = S(X), (3) a third processor means for computing a terminal density X im at which said line is terminated, and (4) a fourth processor means for establishing said gradation control density X c so that a prescribed first difference D between said gradation control density X c and a terminal density X a of said gradation correction curve F(X) agrees within a prescribed error with a second difference D i between said gradation control density X c and said terminal density X im of said line.
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