CN103474046A - Method for improving color reproduction effect from digital camera to displayer - Google Patents

Abstract

The invention provides a method for improving the color reproduction effect from a digital camera to a displayer, and belongs to the field of color science and technology. 24 color lumps of a Macbeth colorchecker color card which is placed in a D65 light box are used as test samples; the RGB value of the 24 color lumps is obtained by taking pictures of the 24 color lumps through the camera; the CIEXYZ value of the 24 color lumps is obtained by means of measurement through a PR715 spectrum scanning colorimeter; the R'G'B' of the displayer corresponding to the CIEXYZ value is calculated through a matrix A and a corresponding equation of the matrix A; the three-channel relation between the RGB of the camera and the R'G'B' of the displayer is built to obtain an R'G'B' image, reproduced on the displayer, of the RGB of any image taken through the camera. The average chromatic aberration obtained through objective evaluation is lowered from 17.1 CIELAB chromatic aberration units before the application of the method to 12.5 CIELAB chromatic aberration units after the application of the method; when subjective vision evaluation is utilized, the improvement rate of the reproduction effect of 30 test samples and 6 standard images adopting the method is increased by 85.6 % compared with the reproduction effect of using the displayer directly.

Description

A kind of method of reproducing effect from the digital camera to the display color that improves

Technical field:

The present invention relates to a kind of raising and reproduce the method for effect from the digital camera to the display color, belong to color science and technical field.

Background technology:

Along with the fast development of computing machine and photoelectric technology, digital image device has been widely used in the various environment such as industry, scientific research and life.Digital image device mainly comprises digital imaging apparatus (as: digital camera, color scanner etc.) and color reproduction equipment (as: display and color printer etc.).Because the color of various vision facilitiess presents the mechanism difference, as different as the RGB of the RGB of the RGB of display and camera, printer, therefore, how between various device, to realize that color transfer and color reproduction have accurately become the study hotspot in this field, generally adopt color management system to realize color reproduction.

Color digital equipment commonly used has camera, scanner, display, printer, also comprises projector.Color management system (Color Management System, CMS) be a kind of input equipment color space transformation to be become to the management software of the another kind of output device color space, purpose is the consistance in order to realize that color is transmitted between distinct device, " What You See Is What You Get " namely often said ^[1-4].For this reason, the international color consortium (International Color Consortium, ICC) of setting up in 1993, be devoted to develop color and administrative standard ^[5].ICC, on the basis of the standard colorimetric CIE XYZ of international lighting association (CIE), has created the format standard (ICC Profile) of the color characteristics file of a characterization device characteristic, for to serve the color management problem of cross-platform environment.1996 by Microsoft (Microsoft) and company of Hewlett-Packard (HP) in proposing sRGB (Standard interchange RGB color space) color space ^[6].And became the standard IEC 611966-2-1 of International Electrotechnical Commission (International Electrotechnical Commission, IEC) in 1998 ^[7], be the profile connecting space that is widely used in the multimedia equipment colouring information exchanges such as computing machine, network.Color management for light based on the ICC standard respectively has relative merits with the color management for light based on the sRGB profile connecting space, complements each other.The former requires the tag file of the equipment that provides, can flexible Application in different color device, but color space mapping operations complexity; The latter requires color device and media to design according to the reference condition ^[8], very flexible, but this pattern does not need complex calculations, can leave the direct communication between the computer realization color device.

Two kinds of different media color reproductions, this is a very complicated technical matters, is the focus of current colorimetry in the world research.Traditional colorimetry under the Orientation observation condition of setting up the 1980s on simple the stimulation can not meet application demand, since the time of nearly 15 years of nineteen nineties, colorimetry starts new round research climax, look looks model (Color Appearance Models wherein, CAM) research is the most active, has proposed multiple model.Look looks MODEL C IECAM02 is proposed in 2002 ^[9], within 2004, CIE has formally published CIECAM02 ^[10], pulled open the prelude of the novel look looks of practical application MODEL C IECAM02.ICC has considered the color reproduction framework by CIECAM02 look looks model ^[11], at present also in research among, do not obtain practical application.

List of references:

[1]L.W.MacDonald,Developments?in?colour?management?systems,Displays,16(4):203-211,1996.

[2]P.A.Rhodes,S.A.R.Scrivener?and?M.R.Luo,ColourTalk-a?system?for?colour?communication,Displays,13(2):89-96,1992.

[3]P.A.Rhodes?and?M.R.Luo,A?system?for?WYSIWYG?colour?communication,Displays,16(4):213-221,1996.

[4]Lindsay?W.MacDonald,Developments?in?colour?management?systems,Displays,16(4),203-211,1996

[5]International?Color?Consortium,http://www.color.org/index.xalter

[6]S.Susstrunk，R.Buckley,etal.Standard?RGB?Color?Spaces.Presented?at?the?Seventh?Color?Imaging?Conference:Color?Science，Systems,and?Applications，127-134，1999.

[7]IEC.Colour?measurement?and?management?in?multimedia?systems?and?equipment?Part2.1:Default?RGB?colour?space-sRGB，61966-2-l,International?Electrotechnical?Commission,1997.

[8]Stokes?M,Anderson?M,Chandrasekar?S,et?al.A?standard?default?color?space?for?the?internet-srgb[J].Microsoft?and?Hewlett-Packard?Joint?Report,1996.

[9]N.Moroney,M.D.Fairchild,C.Li,M.R.Luo,R.W.G.Hunt?and?T.Newman,The?CIECAM02Color?Appearance?Model,Proc.IS&T/SID10th?IS&T/SID?Color?Imaging?Conference,2002.

[10]TC8-01:CIE?Publication159:2004,A?Colour?Appearance?Model?for?Colour?Management?Systems:CIECAM02,2004

[11]Ingeborg?Tastl,Miheer?Bhachech,Nathan?Moroney?and?Jack?Holm,ICC?Color?Management?and?CIECAM02,Hewlett-Packard?Laboratories,Palo?Alto,CA/USA,2005.

Summary of the invention:

The object of the invention is to the problem of the inconsistency of the actual scenery for solving camera and the effect that photo shows on display, and provide a kind of raising to reproduce the method for effect from the digital camera to the display color.

Technical scheme of the present invention is:

24 color lumps of Macbeth colorchecker colour atla that are placed in the D65 lamp box of take are test sample book, camera is clapped to obtain its rgb value, and by its CIEXYZ value of spectrophotometer measurement, adopt matrix A and corresponding equation thereof to calculate R ' G ' B ' of display corresponding to this XYZ value, by setting up camera RGB and the three-channel relation of display R ' G ' B ', obtain camera clap R ' G ' B ' image of reproducing on display of the RGB of arbitrary image.Concrete technology is as follows:

One, environment and instrument and equipment:

(1) darkroom environment

The wall of darkroom environment and ground reflecting rate are with reference to Nissan darkroom standard: the metope reflecting rate is that 60% ground reflecting rate is 20%.

(2) experimental facilities and setting

Digital camera: exposure mode adopts the energy manual mode, and white balance is set to manually, with the grey tank wall of lamp box, makes white balance.

Spectrophotometer: the PR-715 spectrophotometer that adopts Photo Research company.For measuring the CIE XYZ value of sample in lamp box.

Display: adopt CRT monitor.Frequency: 75Hz, resolution is used display to recommend resolution, colour temperature: D65.Experiment is carried out after 2 hours in the display preheating.Display arranges: the white point that at first display is set: display color temperature is set to 6500K or sRGB pattern.Next arranges the TRC(Tone Reproduction Curve of display) characteristic: for CRT monitor, adopt 17 step gray scale bands (Fig. 1) of the gray scale gradual change generally adopted in the world, " contrast " is adjusted to maximum, regulate " brightness " and make band there is contrast variation level, especially note the low-light level band; For LCD display, adopt gray scale and single channel color band: at first " contrast " is adjusted to minimum, regulate " brightness " button and make 17 step gray scale bands (Fig. 1) there is contrast variation level, then regulate " contrast " button and make the colored band of single channel there is contrast variation level.

Light box: adopt X-Rite company standard lamp box.The D65 light source, the geometric condition of lighting source: 0 °/45 °.

Colour atla: the Macbeth ColorChecker of X-Rite company colour atla.

The instrument and equipment that the present invention uses is market and buys.

Two, the concrete steps of the inventive method:

The first step, by the XYZ value of standard white plate and a sample ColorChecker24 tinctorial pattern under spectrophotometer measurement D65 light source.

Second step, calculate by formula (1) (2) rgb value that ColorChecker24 tinctorial pattern shows on display.

$A=\left[\begin{array}{ccc}3.0629& -1.3932& -0.4758\\ -0.9693& 1.8760& 0.0416\\ 0.0679& -0.2289& 1.0694\end{array}\right]$

（1）

$\left[\begin{array}{c}R\\ G\\ B\end{array}\right]=A\×\left[\begin{array}{c}X\\ Y\\ Z\end{array}\right]$ （2）

The 3rd step, R ' G ' B ' value of the sample ColorChecker24 piece colour atla obtained with program (shown in Fig. 2) extraction camera.

The 4th step, to R and R ', G and G ', B and B ', carry out nonlinear fitting, writes out fitting function, and form is as formula (3):

$R_{\mathrm{CRT}}=a_R+b_R\×R_{\mathrm{Camera}}^{n_R}$

$G_{\mathrm{CRT}}=a_G+b_G\×G_{\mathrm{Camera}}^{n_G}$ （3）

$B_{\mathrm{CRT}}=a_B+b_B\×B_{\mathrm{Camera}}^{n_B}$

A in formula (3) _r, b _r, n _rtwo groups of the data least square fittings of R ' and camera R by display obtain; a _g, b _g, n _g, by two groups of the data least square fittings of G ' and camera G of display, obtained; a _b, b _b, n _btwo groups of the data least square fittings of B ' and camera B by display obtain.

The 5th step, camera clap image RGB after formula (3) calculates correction to the image R ' G ' B ' shown on display.

Beneficial effect of the present invention is: method of the present invention is the technical scheme that a kind of color management system is new.Have advantages of that method is easy, cost is low.The image shown on display after the method is processed can be comparatively approaching with the color of actual scenery.

The accompanying drawing explanation:

Fig. 1 is used the gray scale histogram for display is set.

Fig. 2 is program flow diagram.

Fig. 3 is that digital camera arrives CRT monitor color rendering method schematic diagram.

Fig. 4 example 1 checking image is proofreaied and correct front and back effect comparative example figure.

Embodiment:

The embodiment device therefor is commercially available equipment.The concrete steps that realize are with the description of summary of the invention part.

Facilities and equipments SONY CPD-G52021 ' ' CRT monitor and Canon PowerShot G2 digital camera.By 30 test sample books, (the test sample book colour atla: in the CIELAB color space, L gets 50, a, b and gets respectively-40 ,-15,0,15,40, totally 25 kinds of combinations, according to the D65 light source, 2 ° of observer's data are transformed into rgb space by it, add that (rgb value is respectively (50,50,50) (100 to five GTG color lumps, 100,100) (150,150,150) (200,200,200) (255,255,255)) amount to 30 color lumps.With printer, print as test target.), the test sample book in the D65 lamp box and camera are taken test sample book and are directly shown at display, and average color difference between the two is 17.1 CIELAB aberration units; After adopting the method to process, on display, show, average color difference between the two is 12.5 CIELAB aberration units again.Adopt visual evaluation, 30 test sample books and 6 secondary standard images adopt the method than the direct reproduction effect of display improvement rate 85.6% simultaneously.

Claims (4)

1. the method for effect is reproduced in a raising from the digital camera to the display color, it is characterized in that: 24 color lumps of Macbeth colorchecker colour atla that are placed in the D65 lamp box of take are test sample book, camera is clapped to obtain its rgb value, and by its CIEXYZ value of spectrophotometer measurement, adopt matrix A and corresponding equation thereof to calculate R ' G ' B ' of display corresponding to this XYZ value, by setting up camera RGB and the three-channel relation of display R ' G ' B ', obtain camera clap R ' G ' B ' image of reproducing on display of the RGB of arbitrary image.

2. the method for effect is reproduced in raising according to claim 1 from the digital camera to the display color, it is characterized in that: the CIEXYZ value of Macbeth colorchecker colour atla 24 looks under spectrophotometer measurement D65 light source calculates R ' G ' B ' of display corresponding to this XYZ value with formula (1) (2).

$A=\left[\begin{array}{ccc}3.0629& -1.3932& -0.4758\\ -0.9693& 1.8760& 0.0416\\ 0.0679& -0.2289& 1.0694\end{array}\right]$ （1）

$\left[\begin{array}{c}R\\ G\\ B\end{array}\right]=A\×\left[\begin{array}{c}X\\ Y\\ Z\end{array}\right]$ （2）

3. the method for effect is reproduced in raising according to claim 1 from the digital camera to the display color, it is characterized in that: between R ' G ' B ' of the display that the XYZ value that adopts matrix A to calculate is corresponding and camera RGB, be nonlinear relationship, form is as formula (3)

$R_{\mathrm{CRT}}=a_R+b_R\×R_{\mathrm{Camera}}^{n_R}$

$G_{\mathrm{CRT}}=a_G+b_G\×G_{\mathrm{Camera}}^{n_G}$ （3）

$B_{\mathrm{CRT}}=a_B+b_B\×B_{\mathrm{Camera}}^{n_B}$

A in formula (3) _r, b _r, n _rtwo groups of the data least square fittings of R ' and camera R by display obtain; a _g, b _g, n _g, by two groups of the data least square fittings of G ' and camera G of display, obtained; a _b, b _b, n _btwo groups of the data least square fittings of B ' and camera B by display obtain.

4. the method for effect is reproduced in raising according to claim 1 from the digital camera to the display color, it is characterized in that: the image R ' G ' B ' shown on calibrated rear display be by camera clap image RGB through formula (3) calculate.

Images