WO1999056462A1 - Densitometry method - Google Patents
Densitometry method Download PDFInfo
- Publication number
- WO1999056462A1 WO1999056462A1 PCT/GB1999/001256 GB9901256W WO9956462A1 WO 1999056462 A1 WO1999056462 A1 WO 1999056462A1 GB 9901256 W GB9901256 W GB 9901256W WO 9956462 A1 WO9956462 A1 WO 9956462A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- scanner
- image
- document
- control
- digital
- Prior art date
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/59—Transmissivity
- G01N21/5907—Densitometers
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
- H04N1/46—Colour picture communication systems
- H04N1/56—Processing of colour picture signals
- H04N1/60—Colour correction or control
- H04N1/603—Colour correction or control controlled by characteristics of the picture signal generator or the picture reproducer
- H04N1/6033—Colour correction or control controlled by characteristics of the picture signal generator or the picture reproducer using test pattern analysis
Definitions
- This invention relates to a method and apparatus for performing densitometry .
- the process of densitometry is the measurement of optical properties of a material, specifically the optical transmission properties and/or the optical reflection properties of the material. Densitometry is particularly but not exclusively applicable to measuring the optical density (light absorbance or reflectance) and/or colour content of photographic images which have been exposed and processed.
- quality control is commonly based on the use of pre-exposed control tools or reference materials which are processed and/or printed, and then measured for optical density (light absorbance or reflectance) and/or colour content by means of an instrument for performing densitometry.
- control tools or reference materials may be known as control strips, step wedges, printer tests, or monitors.
- the reference materials or samples may be supplied (together with a processed and/or printed sample) by the film manufacturer in a pre-exposed state (under controlled exposure conditions) , or the reference films may be generated using a controlled exposure instrument known as a Sensitometer .
- the reference materials normally contain areas of constant exposure, referred to as 'steps' .
- a densitometer (or apparatus for performing densitometry) is a measuring instrument which provides controlled illumination of the film or paper sample, and one or more photo-cells disposed to be illuminated by light transmitted through or reflected by the sample such that the photo-cell or cells produce a light - dependent output.
- the densitometer measures the photo- cell output, and converts the outputs to a universal measuring scale denoted in "densitometric units" .
- a densitometer will use filtration to sample light intensities at different bands of the visible spectrum, in order to characterise the light intensity in terms of its constituent colours, for example red, green and blue, or cyan magenta and yellow.
- a densitometer output in densitometric units may be manually recorded and used for process control computations, or the densitometer output may alternatively be coupled either directly or indirectly (eg via a modem) to a process control computer.
- the densitometer may additionally be arranged to perform some rudimentary computations and result storage internally.
- a densitometer therefore provides a highly accurate and direct measure of the light transmitted through or reflected from an object.
- such instruments require the use of very high quality optical components to ensure that accurate and reproducible results are obtained.
- sophisticated scientific instruments, such as densitometers are necessarily expensive, and do not have a market size which would allow extensive competition and economies of scale to reduce prices.
- a method of performing densitometry comprising the steps of providing a document or image scanner, inserting a processed pre-exposed control tool or reference material into the scanner in place of a conventional document or image, operating the scanner to produce a digital output which is a measure of the optical density and/or of the colour content of the inserted control tool or reference material, and passing the digital output of the scanner to a digital computing means programmed to analyze the scanner output for the purposes of quality control in the context of image reproduction, such as processing photographic films or papers, reproduction of graphic arts, X-ray films or the like.
- Document or image scanners for scanning and digitising the images on documents are increasingly common in the context of personal computing ("PC"), and present the price and availability advantage concomitant with a large market, competition, and economies of scale.
- a document or image scanner provides controlled illumination of a light source, together with a computer-compatible output representative of colour and density (optical absorbance or reflectance) .
- a document or image scanner in conjunction with a suitably programmed digital computing means (eg a personal computer) enables the combination to perform densitometry and so allows quality control in the context of processing photographic films or papers, particularly in commercial or professional processing of films or papers (whether of visible scenes or objects, or X-ray films, or other images), as well as in the context of other forms of image reproduction.
- a suitably programmed digital computing means eg a personal computer
- apparatus for performing densitometry comprising the combination of a document or image scanner and a digital computing means, the document or image scanner being operable to receive a pre-exposed control tool or reference material in place of a conventional document or image and to scan the control tool or reference material to produce a digital output which is a measure of the optical density and/or the colour content of the received control tool or reference material, the digital computing means being coupled to the document scanner to receive the digital output of the scanner, the digital computing means being programmed to analyze the scanner output for the purposes of quality control in the context of image reproduction, such as processing photographic films or papers, reproduction of graphic arts, X-ray film or the like.
- a commercially available image, film or hardcopy (paper-printed documents) scanner is obtained, being a device capable of digitising images for input to a computer for viewing, manipulation, transmission or storage.
- the scanner comprises light source (s) and light sensor (s), together with the appropriate control circuitry necessary to accomplish the digitisation.
- the output of the scanner is coupled to a personal computer (a self-contained digital computer) .
- the computer is programmed to receive and to process the scanner output in a manner which approximates the optical densities of transmitted or reflected light either at specific wavelengths or through specific filters in respect of a control tool or reference film or sample film or other material being processed by the scanner.
- the filters may be one of a number of the industry-defined colour or density filters, for example "Status A" and "Status M" colour filters.
- a calibration pack of processed film or paper control strips, together with tables of their densitometric values, is also supplied.
- the calibration pack will comprise at least one strip for each of the three photographic filter statuses, and each strip is exposed at a number of discrete levels (usually 21 or more) .
- a flow chart for calibration of the scanner is shown in figure 1.
- a processed control strip from the calibration pack is inserted into a scanner.
- the control strip may be made of negative film 1, positive film 1A or paper IB.
- the control strip is scanned and results stored 3 in a standard digital format such as bit-map.
- the stored image should contain at least 8 bits per colour, which gives a range of intensity values from 0 to 255 for each colour.
- the stored image is analyzed digitally to identify the areas of constant exposure ('steps') and three tables 5 are produced, one for each colour red green and blue.
- This technique gives a mapping or correspondence between density values and the scanned colour intensity values for the photographic filter status of the control strip. This technique should be performed with a sample and table of densitometric values for each of the three photographic filter statuses. The mapping or correspondence is used to calibrate the scanner in order that it may provide an accurate representation of the transmission/reflection density as would be obtainable from a densitometer.
- the use of the scanner along with a digital computer and known densitometric transmission/reflection values allows quality control of photographic printing and the like to be tested without having to use a densitometer for routine measurements.
- the present invention therefore allows the calibration of a scanner to give 7 accurate and inexpensive quality control.
- the present invention may be used as a routine means of quality control by obtaining photographic density values for a control strip and a reference strip as follows.
- the reference strip is scanned and the image stored.
- the image is analyzed to produce 3 tables giving the colour intensity value (0 to 255 or greater) for red, green and blue.
- the appropriate red, green or blue colour intensity to density look-up tables are selected depending on the photographic filter.
- a statistical analysis is performed, as above, to determine the densitometric values of the reference strip from the scanned colour intensity values.
- a control strip is scanned and its densitometric values obtained.
- the present invention also allows the routine comparison of photographic materials.
- a processed sample of a material with known densitometric characteristics is scanned and the density values are obtained from the scanner, as above.
- the unknown sample which has been processed in the same conditions as the known material is scanned and the photographic densities are determined. From the comparison of the densitometric values of the two samples, the difference in photographic parameters, such as speed or contrast or any such calculation as may be performed on the densitometric values can be determined.
- the present invention may be used as a means of determining the print quality of a printer by scanning a test print, determining the photographic densities of the test print as above. The quality of subsequent prints can be determined by comparison with the density values obtained from the test print .
- Improved performance can be obtained by various measures (alone or in any suitable combination) , such as use of a more accurate scanner, use of more robust algorithms to approximate optical densities, use of known standard inputs to characterise hardware and system responses, and use of other such improvements.
- the present invention could be used as a spectrophotometer , by being adapted to analyze the intensity of each colour or band of wavelength in an optical spectrum.
- the steps of filtering the light source or photocells may be included.
- digital scanner and computing means could be incorporated into a single dedicated unit for the purpose of the present invention.
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- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Spectrometry And Color Measurement (AREA)
- Investigating Or Analysing Materials By Optical Means (AREA)
- Facsimiles In General (AREA)
Abstract
Description
Claims
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2000546514A JP2002513252A (en) | 1998-04-28 | 1999-04-23 | Concentration measurement method |
AU36194/99A AU3619499A (en) | 1998-04-28 | 1999-04-23 | Densitometry method |
EP99918162A EP1076992A1 (en) | 1998-04-28 | 1999-04-23 | Densitometry method |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GBGB9808968.3A GB9808968D0 (en) | 1998-04-28 | 1998-04-28 | Densitometry and/orspectrophotometry method |
GB9808968.3 | 1998-04-28 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1999056462A1 true WO1999056462A1 (en) | 1999-11-04 |
Family
ID=10831050
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/GB1999/001256 WO1999056462A1 (en) | 1998-04-28 | 1999-04-23 | Densitometry method |
Country Status (6)
Country | Link |
---|---|
EP (1) | EP1076992A1 (en) |
JP (1) | JP2002513252A (en) |
CN (1) | CN1298600A (en) |
AU (1) | AU3619499A (en) |
GB (1) | GB9808968D0 (en) |
WO (1) | WO1999056462A1 (en) |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN103674492B (en) * | 2013-11-29 | 2016-08-17 | 天津大学 | Automatic darkening welding filter lens diffused light reduction luminance factor measuring method |
Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO1992015957A2 (en) * | 1991-03-04 | 1992-09-17 | Eastman Kodak Company | Production of second-generation camera-original control tool photographies via photography of digitally-generated transparency of an original scene |
EP0525964A2 (en) * | 1991-06-25 | 1993-02-03 | Scitex Corporation Ltd. | Apparatus and method for color calibration |
US5241406A (en) * | 1990-01-18 | 1993-08-31 | X-Ray Scanner Corporation | X-ray film scanning and digitizing apparatus |
EP0562971A1 (en) * | 1992-03-23 | 1993-09-29 | Eastman Kodak Company | Method and apparatus for adaptive color characterization and calibration |
WO1995021502A1 (en) * | 1994-02-02 | 1995-08-10 | Electronics For Imaging, Inc. | Method and apparatus for converting color scanner signals into colorimetric values |
EP0707413A2 (en) * | 1994-10-13 | 1996-04-17 | Kodak Limited | A method for improving the contrast in photographic film materials |
-
1998
- 1998-04-28 GB GBGB9808968.3A patent/GB9808968D0/en not_active Ceased
-
1999
- 1999-04-23 JP JP2000546514A patent/JP2002513252A/en active Pending
- 1999-04-23 WO PCT/GB1999/001256 patent/WO1999056462A1/en not_active Application Discontinuation
- 1999-04-23 AU AU36194/99A patent/AU3619499A/en not_active Abandoned
- 1999-04-23 CN CN 99805587 patent/CN1298600A/en active Pending
- 1999-04-23 EP EP99918162A patent/EP1076992A1/en not_active Withdrawn
Patent Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5241406A (en) * | 1990-01-18 | 1993-08-31 | X-Ray Scanner Corporation | X-ray film scanning and digitizing apparatus |
WO1992015957A2 (en) * | 1991-03-04 | 1992-09-17 | Eastman Kodak Company | Production of second-generation camera-original control tool photographies via photography of digitally-generated transparency of an original scene |
EP0525964A2 (en) * | 1991-06-25 | 1993-02-03 | Scitex Corporation Ltd. | Apparatus and method for color calibration |
EP0562971A1 (en) * | 1992-03-23 | 1993-09-29 | Eastman Kodak Company | Method and apparatus for adaptive color characterization and calibration |
WO1995021502A1 (en) * | 1994-02-02 | 1995-08-10 | Electronics For Imaging, Inc. | Method and apparatus for converting color scanner signals into colorimetric values |
EP0707413A2 (en) * | 1994-10-13 | 1996-04-17 | Kodak Limited | A method for improving the contrast in photographic film materials |
Also Published As
Publication number | Publication date |
---|---|
GB9808968D0 (en) | 1998-06-24 |
CN1298600A (en) | 2001-06-06 |
EP1076992A1 (en) | 2001-02-21 |
AU3619499A (en) | 1999-11-16 |
JP2002513252A (en) | 2002-05-08 |
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