CN106878705B - A kind of chromaticity assessment method of number hard copy output sRGB images - Google Patents
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Abstract
The present invention relates to the chromaticity assessment methods that a kind of digital hard copy exports sRGB images, belong to digital hard copy colour export technique field.It chooses at least three kinds typical memory colours and extracts the several groups RGB color value of a variety of lightness and saturation degree from several standards sRGB images, square digital color lump is made and arranges all color lumps, using color lump digitized video as test and appraisal colour code；Using test and assess colour code image and standard sRGB images as image group, L is determined*、C* ab、h* abThree change curves of the optimum colour and acceptable colour cast limit that value is arranged with test colour code color lump, as comparison curve；With test and appraisal colour code and curve is compared, is tested and assessed to the sRGB image output chromaticities of output equipment system.It is convenient, fast this method avoid the otherness of common subjective evaluation method, unstability, it is suitable for the sRGB colors of image quality evaluation of digital hard-copy output device and analysis in development and application field.
Description
Technical field
The present invention relates to the chromaticity assessment methods that a kind of digital hard copy exports sRGB images, and this method is for various
The measurement and evaluation of the chromaticity of digital hard copy device output sRGB images belong to digital hard copy colour export technique neck
Domain.
Background technology
Nowadays various hard copy colour exports are very common in our life.Either the portrait album of high quality,
The slightly worse street corner product manual of image quality, the advertising poster being still seen everywhere are required for hard copy device to export digitized video
It is presented on to stock, and it is therein most of for sRGB images.
SRGB is a kind of mark for being used for display, printer and internet that Hewlett-Packard developed with Microsoft in 1996 together
Quasi- rgb color space.Currently, it is widely used in the industries such as display, photography, output as a standard, many disappears in the market
Taking type digital camera, scanner and printer etc. all uses sRGB models as default mode or only color space.With
Be mutually connected, shoot or scan the sRGB digitized video hard copies formed and export accurate color reproduction, be to output equipment face
The core requirement of color performance.But hard-copy output device type currently on the market is various, and chromaticity is irregular, needs
The chromaticity assessment method of effect.
The digitizing technique again of output sample, root are mainly based upon to the profession research of output image color quality evaluation
According to the pixel color value of output sample digitized video, by the mean square error (MSE) with original copy color value, Y-PSNR (PSNR), knot
The models such as structure similarity (SSIM) carry out the chromaticity of evaluation image output.On the one hand, such methods belong to image integral color
The overall merit of accuracy can not pointedly characterize and analyze the reproduction quality of wherein different colours；On the other hand, base
It is compared in the Pixel-level of image, the digitized video of duplicate need to be obtained by CCD imaging devices, and be converted by Color Management Technology
Coloration image, process is complicated, and technology requires high.Therefore, such method is unsuitable for produce reality application.And it is used at present in practicality
Method be mostly to rely on subjective visual evaluation, but the factors such as observing environment and Observation personnel and experience are affected, and process is cumbersome,
Unstable result cannot give the evaluation result of objective quantification.To sum up, a kind of hard copy output color based on objective measurement is established
Color quality evaluation method is needed for production application.
Business image is mostly based on personal portrait, natural views and scenery, and human eye is to the colour of skin therein, sky blue and typical case
Plant color (such as grass green and rape flower yellow) is most sensitive, these colors become the key of whole image reproduction quality.
Invention content
In consideration of it, the present invention examining using the reproduction quality of typical memory colour as digital hard copy output color quality evaluation
It investigates a case and then decide what to do the heart, a kind of method that can characterize and evaluate hard copy output color quality is provided.
The present invention devises the typical memory colour color character such as the reflection colour of skin, sky blue, grass green and rape flower yellow
Test and assess colour code, in conjunction with visual valuation test, define human eye vision color most preferably and acceptable colour cast limit, from CIEL*
C* abh* abThe chromaticity of three each memory colours of dimensional representation of coloration, and then characterize the quality of colour of image entirety.
A kind of chromaticity assessment method of number hard copy output sRGB images, includes the following steps：
(1) at least three kinds typical memory colours are chosen, for each memory colour, from several standards sRGB images, extraction is more
The several groups RGB color value of kind of lightness and saturation degree, every group of RGB color value form the digital color lump of a square, and by all color lumps
Arrangement, using the color lump digitized video of each obtained typical memory colour as test and appraisal colour code；
(2) using the standard sRGB images of test and assess colour code image and extraction colour code color as image group, to each memory colour, really
Its fixed L*、C* ab、h* abThe acceptable colour cast limit that value becomes larger and becomes smaller with the optimum colour and color value of test colour code color lump arrangement
Three change curves, the comparison curve as each typical memory colour；
(3) using test and appraisal colour code and comparison curve, the sRGB image output chromaticities of output equipment system are surveyed
It comments, includes the following steps：
1) the output test and appraisal colour code sample under the normal output condition of equipment；
2) colorimeter is used, identical test condition measures the test and appraisal colour code of reality output when selecting to compare curve with determination
The L of each color lump in sample*C* abh* abChromatic value；
3) by the L of each memory colour test and appraisal colour code color lump measured in step 2)*、C* ab、h* abChromatic value presses corresponding color lump
Serial number is drawn in curve and is compared with the corresponding curve that compares, by curve comparison, in terms of lightness, saturation degree and form and aspect three
Characterize and evaluate the chromaticity of each memory colour.
In step (1), it is used to export the standard that visual color is evaluated from the printing devices such as Hewlett-Packard and software supplier
In sRGB images, for each typical memory colour of selection, the several groups RGB color value of a variety of lightness and saturation degree is extracted, is owned
RGB color value is respectively formed digital square color lump and arranges, and constitutes the RGB image files of * .GIF or * a .bmp format, makees
For the test and appraisal colour code of typical case's memory colour.
The typical memory colour includes that (such as grass green and rape flower are yellow for the common colour of skin, sky blue and typical plant color
Color) etc..The colour of skin, sky blue, grass green and the typical memory colour of four kinds of rape flower yellow have been selected in the present invention.For each memory
Color, the standard sRGB images for extracting RGB color value (colour code color) are no less than 5 width, need to embody the lightness of typical memory colour,
Form and aspect and saturation degree variation range.The color lump number of each typical case's memory colour is no less than 15 in the test and appraisal colour code, needs to embody
The variation characteristic of typical case memory chromatic luminosity, form and aspect and saturation degree.The size of color lump needs to accord in the test and appraisal colour code image
Close the requirement of output color lump color homogeneity and measuring instrument test aperture.
In step (2), the determination method of the comparison curve of each typical memory colour comprises the following specific steps that：
I) using the standard sRGB images of test and assess colour code image and extraction colour code color as image group, according to sRGB and CIE colors
The correspondence of degree is converted to L together*C* abh* abColoration image；Based on this, then respectively increase and reduce L*、C* ab、h* abValue
Several are formed with different L*C* abh* abThe image group of coloration；
Ii) selection colour gamut is more than the hard copy printout output equipment of sRGB colour gamuts, and equipment is carried out colorimetric characterization；It utilizes
Color Management Technology, by all L in step i)*C* abh* abThe image group of coloration prints out；
Iii) it is directed to step ii) the image group pattern that prints, each memory colour is respectively according to L*、C* ab、h* abWhat is be worth is big
Small variation is ranked sequentially, and under the conditions of standard observation, is tested, is selected by subjectivity test and appraisal by the normal observer of colour vision
Just the acceptable and color value colour cast degree in variation that becomes smaller is just acceptable for colour cast degree in variation that color is best and color value becomes larger
Image pattern (is known as the acceptable colour cast limit pattern that color value becomes larger, becomes smaller)；
Iv it) to each memory colour, measures color respectively by colorimeter and most preferably and in acceptable colour cast limit pattern product tests and assesses
The L of colour code color lump*C* abh* abChromatic value is respectively formed L*、C* ab、h* abThe optimum colour and be subjected to inclined that value is arranged with colour code color lump
Three change curves of color limit, the comparison curve as the memory colour.Each typical memory colour, is all respectively formed L*、C* ab、
h* abThree groups of each three change curves.
In above-mentioned steps i), the image group L*、C* ab、h* abThe amplitude of variation that value increases and reduces, can be real by exporting
Determination is tested, selection can just have the amplitude of variation of visual color difference under the conditions of standard observation.It is described that there are different L*C* abh* ab
The number of the image group of coloration refers in the case where the color value amplitude of variation that previous experiments select is changed stepwise, and reaches output pattern color
Number widely different with memory colour and required cannot receive when.
Above-mentioned steps iii) in, the standard observation condition is D65 or D50 standard sources and 2000lx ± 300lx
The illumination of left and right.The subjective test and appraisal experiment need to be completed by being no less than 8 visions and the normal observer of colour vision, and with selected
The average color angle value of tinctorial pattern is evaluation result.
Above-mentioned steps iv) in, the colorimeter measures the L of test and appraisal colour code color lump*C* abh* abChromatic value is selected and subjectivity
Phase is observed with the light source of colour temperature and 2 ° of visual angles.
In the step 3) of step (3), during characterizing and evaluating the chromaticity of each memory colour of sample, work as sample
Test and appraisal colour code color lump chroma curve close to corresponding best curve (the optimum colour curve) for comparing curve when, show to export sample
The memory colour color representation it is preferable；And when the chromatic value curve of the test and appraisal colour code color lump of sample deviates corresponding comparison curve most
Good curve is more, but when in two acceptable limit curve ranges, then show the memory colour color table for exporting sample
Now it is subjected to；With this, the overall color quality of sRGB image output samples is characterized by the chromaticity of all typical memory colours.
The chromaticity assessment method of the digital hard copy output sRGB images of the present invention, by exporting, measuring test and appraisal color
Mark the L of color*C* abh* abChromatic value curve, and by with the comparison and analysis that accordingly compare curve, from multiple typical memory colours
The chromaticity of chromaticity comprehensive characterization general image.This method avoid the otherness of common subjective evaluation method, shakinesses
The methods of qualitative and image aberration mean square error color specific aim missing the deficiencies of, it is convenient, fast, be suitable for exploitation and
The image color quality test and appraisal and analysis of digital hard-copy output device in application field.
Description of the drawings
Fig. 1-1 is the 25 width personal portrait class images selected.
Fig. 1-2 is the 12 width sky scape class images selected.
Fig. 1-3 is the 10 width meadow landscape class images selected.
Fig. 1-4 is the 9 width rape flower landscape class images selected.
Fig. 2-1 is the colour of skin chosen area example of a personal portrait image.
Fig. 2-2 is the sky blue chosen area example of a sky scape image.
Fig. 2-3 is the grass green chosen area example of a meadow landscape image.
Fig. 2-4 is the yellow chosen area example of a rape flower image.
Fig. 3-1 is colour of skin L*=65 characteristic point chooses example.
Fig. 3-2 is sky blue L*=60 characteristic point chooses example.
Fig. 3-3 is grass green L*=50 characteristic point chooses example.
Fig. 3-4 is rape flower yellow L*=85 characteristic point chooses example.
Fig. 4-1 is the complexion evaluation colour code of 120 color lumps.
Fig. 4-2 is the sky blue test and appraisal colour code of 45 color lumps.
Fig. 4-3 is the grass green test and appraisal colour code of 50 color lumps.
Fig. 4-4 is the rape flower yellow test and appraisal colour code of 15 color lumps.
Fig. 5-1 is that ratio of skin tone is optimal to vision in curve and the brightness value L of acceptable limit*Compare curve.
Fig. 5-2 is that sky blue compares in curve that vision is optimal and the brightness value L of acceptable limit*Compare curve.
Fig. 5-3 is that grass green compares in curve that vision is optimal and the brightness value L of acceptable limit*Compare curve.
Fig. 5-4 is that rape flower yellow compares in curve that vision is optimal and the brightness value L of acceptable limit*Compare curve.
Fig. 6-1 is that ratio of skin tone is optimal to vision in curve and the chroma value C of acceptable limit* abCompare curve.
Fig. 6-2 is that sky blue compares in curve that vision is optimal and the chroma value C of acceptable limit* abCompare curve.
Fig. 6-3 is that grass green compares in curve that vision is optimal and the chroma value C of acceptable limit* abCompare curve.
Fig. 6-4 is that rape flower yellow compares in curve that vision is optimal and the chroma value C of acceptable limit* abCompare curve.
Fig. 7-1 is that ratio of skin tone is optimal to vision in curve and the hue angle value h of acceptable limit* abCompare curve.
Fig. 7-2 is that sky blue compares in curve that vision is optimal and the hue angle value h of acceptable limit* abCompare curve.
Fig. 7-3 is that grass green compares in curve that vision is optimal and the hue angle value h of acceptable limit* abCompare curve.
Fig. 7-4 is that rape flower yellow compares in curve that vision is optimal and the hue angle value h of acceptable limit* abCompare curve.
Fig. 8-1 is that two kinds of different papers export the colour of skin brightness ratio of sample to curve.
Fig. 8-2 is the colour of skin chroma comparison curve that two kinds of different papers export sample.
Fig. 8-3 is the skin tone angle comparison curve that two kinds of different papers export sample.
Fig. 9-1 is that two kinds of different papers export the sky blue brightness ratio of sample to curve.
Fig. 9-2 is the sky blue colorfulness comparison curve that two kinds of different papers export sample.
Fig. 9-3 is the sky blue hue angle comparison curve that two kinds of different papers export sample.
Figure 10-1 is that two kinds of different papers export the grass green brightness ratio of sample to curve.
Figure 10-2 is the grass green colorfulness comparison curve that two kinds of different papers export sample.
Figure 10-3 is the grass green hue angle comparison curve that two kinds of different papers export sample.
Figure 11-1 is that two kinds of different papers export the rape flower yellow brightness ratio of sample to curve.
Figure 11-2 is the rape flower yellow chroma comparison curve that two kinds of different papers export sample.
Figure 11-3 is the rape flower yellow tone angle comparison curve that two kinds of different papers export sample.
Specific implementation mode
Illustrate that the design of Te st grogram and the specific of output color quality were evaluated below in conjunction with the drawings and specific embodiments
Journey, to further illustrate the present invention.
1, the generation of test and appraisal colour code
1., collect the standard sRGB images of each printing device and software company for image output color evaluation, Cong Zhongxuan
It is several to select the image containing typical memory colour.Actual selection 25 width of personal portrait, 12 width of blue sky landscape, 10 width of meadow landscape, with
And 9 width of rape flower, as shown in Fig. 1-1~Fig. 1-4.It is respectively used to the digital face of the colour of skin, sky blue, grass green and rape flower yellow
Color extracts.To every width image, its several lightness and the more uniform memory character color of the representational color of saturation degree are chosen
SRGB color value of its average RGB value as the region color is extracted in region.As shown in Fig. 2-1~Fig. 2-4, respectively a portrait, indigo plant
Its landscape, meadow landscape and rape flower image get colors the example in region.Portrait type, blue sky landscape class, meadow class and rape
Flower class image has chosen 900,512,498 and 138 more uniform color regions and corresponding RGB arrays altogether respectively, according to sRGB
It is converted into L with the correspondence of cie color*a*b*Chromatic value.
2., each memory colour L for 1. obtaining of process*a*b*Aberration very little between some possible colors in color, it is not necessary that all select
With.Effective color value can be in the L 1. defined by process*a*b*Color point is uniformly taken to determine in distribution.For this purpose, dividing first
The brightness value L of each memory colour is analysed*Distribution；Then, respectively from its minimum lightness L* min(colour of skin, sky blue, grass green and
Rape flower yellow is respectively 25,30 and 70) starts, with △ L*=5 be lightness interval, determines L*+△L*Included face in range
The a of color*b*Figure；Finally, in a*b*Point uniformly gets colors a little in enclosed region, and records its L*a*b*Value.Such as Fig. 3-1~Fig. 3-
Shown in 4, respectively portrait type image L*=65, blue sky landscape class image L*=60, meadow landscape class image L*=50, rape flower
Class image L*=85 characteristic point chooses result.If so, being directed to colour of skin class, blue sky class, meadow class and rape flower class image, it is divided into
178,102,112 and 47 feature color dots are not had chosen.
3., further, by colour difference formula Δ Eab *=(Δ L*2+Δa*2+Δb*2)1/2, 2. each memory colour that process is chosen
Color difference analysis is carried out between feature.If the aberration Δ E between two featuresab *＜ 2 then only retains one of feature.So
Screening, the colour of skin, sky blue, grass green and rape flower yellow characteristic chromatic number mesh are ultimately determined to 120,45,50 and 15.Thereafter,
By these L*a*b*Color value is converted to corresponding rgb value according to sRGB with the relationship of cie color value, such as " colour code color in 1~table of table 4
Shown in block serial number and color value " column data.
4., by process 3. in the rgb value that determines generate each typical memory colour * .GIF formats digital color lump images,
It tests and assesses colour code.Respectively as shown in Fig. 4-1~Fig. 4-4.
2, map generalization is tested
Choose 10 width of portrait portrait image, 11 width of blue sky landscape image, 9 width of meadow landscape image and 9 width of rape flower image
Test chart is formed with each test and appraisal colour code.Further, test chart is transformed to L*C* abh* abDigitized video changes to constant gradient respectively
Its L*、C* ab、h* ab(maximum changing range of colour of skin coloration is L to value*±10、C* ab- 6~C* ab+14、h* ab± 12, sky blue chroma color
Maximum changing range be L*±14、C* ab- 12~C* ab+20、h* ab- 18~h* ab+ 8, grass green coloration variation maximum magnitude is L*-2
~L*+12、C* ab- 18~C* ab+20、h* ab- 2~h* ab+ 10, it is L that rape flower coloration, which changes maximum magnitude,*- 10~L*+8、Cab*-
12~Cab*+14、h* ab- 1~h* ab+ 4) RGB images are converted back, and again.The series of tests figure is for simulating various colour cast outputs
Situation.
3, the printout of test chart
Epson L1800 ink-jet printers and Epson photographic quality Alhue paper is selected to constitute the output of digitized video
System.Color characteristics are exported to it and have carried out colour gamut analysis, it was demonstrated that its colour gamut is much larger than sRGB colour gamuts.Thereafter, color pipe is utilized
Techniqueflow is managed, the test chart image (color of each memory colour colour code color lump after normal coloration and several change colorations is printed out
Angle value is in printer output gamut range).
4, the color subjective assessment of test chart sample is exported
To several test chart samples of output, visual subjective assessment is carried out.I.e. in standard observation environment (D65 standards
White light, 2300lx illumination) under, normal by eyesight and colour vision and with certain color knowledge 10 observers are observed.
It is required that observer selects colour vision most from the series of drawing sample that lightness, chroma, hue angle numerical value are changed by constant gradient respectively
Excellent and visually-acceptable maximum colour cast pattern.Experiment is in triplicate.
5, chromaticity compares the determination of curve
Each memory colour colour vision of previous experiments determination under D65 light sources and 2 ° of test conditions is measured using colorimeter most
The L of colour code color lump on excellent and maximum acceptable colour cast pattern*C* abh* abChromatic value, and measure and be averaged three times.
Thereafter, respectively by the optimal corresponding L of each memory colour colour vision*It is worth ascending ascending sort, forms each memory
The L of color*Optimal comparison curve；Meanwhile according to the L*The color lump number of value ascending order puts in order, and forms L*The upper and lower limit variation of value is bent
Line, i.e., visually-acceptable lightness variation limit compare curve.Three curves characterize corresponding the best of memory chromatic luminosity and regard
Feel output color and acceptable deviation range.It is formed by each typical memory colour L*Value compares curve such as Fig. 5-1~Fig. 5-4 institutes
Show.
Similarly, the C of each typical memory colour is obtained* ab、h* abCurve is compared, respectively such as Fig. 6-1~Fig. 6-4 and 7-1~figure
Shown in 7-4.
Each typical case's memory colour compares the L of curve*C* abh* ab" brightness ratio is to curve numerical value " in data such as 1~table of table 4,
" upper limit curve ", " optimal curve " and " lower limit curve " in " chroma compares curve numerical value " and " hue angle compares curve numerical value "
Shown in column data.
6, the application of assessment method
The application process and analysis method of assessment method are as follows：
To the test and appraisal colour code sample of normal print output, test condition as required measures its each memory colour test and appraisal colour code color
The cie color value of block, draws its L respectively*、C* ab、h* abCurve, and done in one drawing with the corresponding curve that compares, with regard to L*、C* ab、h* abColoration is analyzed respectively.
The colour code chroma curve for exporting sample is closer with the best curve compared in curve, shows the color of the output color
Degree variation is closer with vision optimum colour situation；If colour code chroma curve deviates its optimal comparison curve, but disposed thereon, lower limit
Between comparing curve, then show that the color of output coloration variation vision is acceptable；And when beyond the above situation, then show defeated
Vision requirement cannot be met by going out color.
If so, can be from typical memory colour and its L*、C* ab、h* abThe angle of three color attributes, to the image of output with
The due colour vision effect of sRGB images gives the quantization signifying of otherness, and then comprehensive characterization its overall color quality.
An application example is set forth below.
Epson L1800 ink-jet printers are still used, respectively using two different Paper Printings test and appraisal colour code and choosing
SRGB images.
Using colorimeter, select D65 light sources, 2 ° of visual angles measuring condition, measure printout pattern and (be referred to as sample
1, sample 2) test and appraisal each memory colour color lump of colour code L*C* abh* abChromatic value, and the corresponding color lump serial number given by 1~table of table 4
Curve is drawn in be compared with the corresponding curve that compares.
The L that colour of skin situation is drawn*、C* ab、h* abCurve is respectively shown in Fig. 8-1~Fig. 8-3.
The case where Fig. 8-1 can be shown that, the lightness size and its amplitude of variation of 1 the showed colour of skin of sample are compared with sample 2 is closer
Lightness optimal curve shows that its brightness variation and contrast can preferably meet visual demand.And the case where sample 2, is then relatively whole
Body is partially bright, especially in shadow area of skin color；Meanwhile the variation range of lightness becomes smaller, and shows that the colour of skin that sample 2 shows is integrally inclined
Bright, the darkness at shadow position is obviously insufficient, and level contrast is relatively low.
Similarly, Fig. 8-2 shows the case where saturation degree of 1 the showed colour of skin of sample is compared with sample 2 closer to the optimal song of chroma
Line, and registration is higher, shows can there is preferable visual effect.And the case where sample 2, then whole saturation degree was insufficient, especially existed
High light area of skin color, it is unacceptable for vision.Show that the colour of skin saturation degree of sample 2 is obviously relatively low, it is due red to lack the colour of skin
Profit and life, especially in the light tones such as forehead, face region.
Similarly, the case where Fig. 8-3 is provided, and the hue angle of 1 the showed colour of skin of sample is compared with sample 2 is optimal closer to hue angle
Curve, it is whole all in acceptable visual range, show more consistent with the form and aspect of visual memory.And the case where sample 2 then phase
It is less than normal to entirety, it has been significantly less than vision acceptable limit.Show the colour of skin form and aspect excessively magenta cast of sample 2, visual sense feeling
Apparent colour cast.
The color of the portrait colour of skin of the two samples of visual comparison, sample 1 is natural, ruddy, there is life, bias colour, lightness
Variation range is big, and picture level is abundant, and details does very well；And the then whole of sample 2 lacks life, level of detail performance is insufficient,
Skin lightening colour cast color is apparent, it is difficult to receive.This matches with the case where passing through tracing analysis.
The L that sky blue, grass green and rape flower yellow situation are drawn*、C* ab、h* abCurve is respectively Fig. 9-1~Fig. 9-
3, shown in Figure 10-1~Figure 10-3 and Figure 11-1~Figure 11-3.
These three typical memory colours it is similar analysis shows：The colour brilliance curve of sample 1 is all optimal bright close to its vision
It writes music line, and sample 2 then all deviates that the optimal lightness curve of vision is more, and sky blue, grass green chromatic luminosity are bigger than normal (partially bright), rape
Flower yellow lightness is then less than normal (partially dark), and more lightness has exceeded vision acceptable limit.Similarly, the chroma curve of sample 1
Also it is all closer to its vision optimal curve.Although the high saturation color of rape flower yellow and the chroma value of weak colour are dropped
It is low, but in addition to the color change of individual point characterizations is larger, it is whole still in vision acceptable limit.And the case where sample 2, is then
The chroma of all these three colors is all apparent insufficient, is nearly all less than its visually-acceptable minimum limit.Finally, sample 1
Form and aspect angular curve is all very close to its vision optimal curve, and the case where sample 2 is sky blue and rape flower yellow compared with its vision
Optimal curve is less than normal, grass green it is bigger than normal compared with its vision optimal curve, and be more than its acceptable limit more.
Visual comparison has been carried out to two samples, has found sky blue, meadowbrook and rape flower yellow on sample 1
Color is accurate, and color is beautiful, and level is abundant clear, vision satisfaction.In contrast, the color on sample 2 is then apparent is not enough saturated,
It is not achieved bright-coloured degree in kind in impression, shade and contrast also relative deficiency, and the form and aspect of color are compared with equal on sample 1
There are obvious deviation, the form and aspect of especially rape flower yellow relatively orange, hence it is evident that deviate the impression of color in kind.
Preferable coincide of the above comparison analysis and actual observation shows：The L obtained by using test and appraisal colour code color lump*、C* ab、h* abChange curve, and with the comparison that accordingly compares curve, print effect can be carried out to particular color in lightness, saturation degree
With the characterization of three aspect of form and aspect；The quality characterization of numerous typical case's memory colours, and the colour reproduction quality of image entirety can be given
More comprehensively characterization and analysis.
The above results are only caused by paper difference, to the influence degree that two kinds of paper of objective characterisation export color,
Quantitative basis is provided for the selection of paper.
Those of ordinary skills in the art should understand that：The above is only a specific embodiment of the present invention, and
It is not used in the limitation present invention, all within the spirits and principles of the present invention, any modification, equivalent substitution, improvement and etc. done,
It should be included within protection scope of the present invention.
Claims (10)
1. a kind of chromaticity assessment method of number hard copy output sRGB images, includes the following steps：
(1) at least three kinds typical memory colours are chosen, for each memory colour, from several standards sRGB images, extraction is a variety of bright
The several groups RGB color value of degree and saturation degree, every group of RGB color value forms the digital color lump of a square, and all color lumps are arranged,
Using the color lump digitized video of each obtained typical memory colour as test and appraisal colour code；
(2) it is determined to each memory colour as image group using the standard sRGB images of test and assess colour code image and extraction colour code color
L*、C* ab、h* abThe acceptable colour cast limit that value becomes larger and becomes smaller with the optimum colour and color value of test colour code color lump arrangement respectively
Each three change curves, the comparison curve as each typical memory colour；
(3) it using test and appraisal colour code and comparison curve, tests and assesses, wraps to the sRGB image output chromaticities of output equipment system
Include following steps：
1) the output test and appraisal colour code sample under the normal output condition of equipment；
2) colorimeter is used, identical test condition measures the test and appraisal colour code sample of reality output when selecting to compare curve with determination
In each color lump L*C* abh* abChromatic value；
3) by the L of each memory colour test and appraisal colour code color lump measured in step 2)*、C* ab、h* abChromatic value is painted by corresponding color lump serial number
Be compared with the corresponding curve that compares at curve, by curve comparison, in terms of lightness, saturation degree and form and aspect three characterization and
Evaluate the chromaticity of each memory colour.
2. the chromaticity assessment method of number hard copy output sRGB images according to claim 1, it is characterised in that：
The typical memory colour includes the colour of skin, sky blue and typical plant color.
3. the chromaticity assessment method of number hard copy output sRGB images according to claim 1, it is characterised in that：
For each memory colour, the standard sRGB images for extracting RGB color value are no less than 5 width；Each typical case in the test and appraisal colour code
The color lump number of memory colour is no less than 15.
4. the chromaticity assessment method of number hard copy output sRGB images according to claim 1, it is characterised in that：
The determination method of the comparison curve of each typical memory colour, comprises the following specific steps that：
I) it will test and assess and colour code image and extract the standard sRGB images of colour code color as image group, according to sRGB and cie color
Correspondence is converted to L together*C* abh* abColoration image；Based on this, then respectively increase and reduce L*、C* ab、h* abValue is formed
Several are with different L*C* abh* abThe image group of coloration；
Ii) selection colour gamut is more than the hard copy printout output equipment of sRGB colour gamuts, and equipment is carried out colorimetric characterization；Utilize color
Administrative skill, by all L in step i)*C* abh* abThe image group of coloration prints out；
Iii) it is directed to step ii) the image group pattern that prints, each memory colour is respectively according to L*、C* ab、h* abThe size variation of value
It is ranked sequentially, under the conditions of standard observation, is tested by subjectivity test and appraisal by the normal observer of colour vision, select color most
The just acceptable striograph of colour cast degree in variation that good and color value becomes larger that colour cast degree in variation is just acceptable and color value becomes smaller
Sample；
Iv) to each memory colour, measured respectively by colorimeter color most preferably and acceptable colour cast limit pattern in test and assess colour code color
The L of block*C* abh* abChromatic value is respectively formed L*、C* ab、h* abValue respectively with colour code color lump arrangement optimum colour and color value become larger and
Each three change curves of the acceptable colour cast limit to become smaller, the comparison curve as typical case's memory colour.
5. the chromaticity assessment method of number hard copy output sRGB images according to claim 4, it is characterised in that：
The image group L*、C* ab、h* abThe amplitude of variation that value increases and reduces is determined by exporting experiment, is selected in standard observation
Under the conditions of can just have the amplitude of variation of visual color difference.
6. the chromaticity assessment method of number hard copy output sRGB images according to claim 4, it is characterised in that：
It is described that there are different L*C* abh* abThe number of the image group of coloration, in the case where color value amplitude of variation is changed stepwise, to reach output figure
Sample color and memory colour are widely different and number that cannot receive when is required.
7. the chromaticity assessment method of number hard copy output sRGB images according to claim 4, it is characterised in that：
The standard observation condition is D65 or D50 standard sources and the illumination of 2000lx ± 300lx.
8. the chromaticity assessment method of number hard copy output sRGB images according to claim 4, it is characterised in that：
The subjective test and appraisal experiment is completed by being no less than 8 visions and the normal observer of colour vision, and with the average color of selected tinctorial pattern
Angle value is evaluation result.
9. the chromaticity assessment method of number hard copy output sRGB images according to claim 4, it is characterised in that：
The colorimeter measures the L of test and appraisal colour code color lump*C* abh* abChromatic value, using with subjective observation phase with the light source of colour temperature and
2 ° of visual angles.
10. the chromaticity assessment method of number hard copy output sRGB images according to claim 1, feature exist
In：During characterizing and evaluating the chromaticity of each memory colour of sample, when the chroma curve of the test and appraisal colour code color lump of sample
When close to the corresponding best curve for comparing curve, show that the memory colour color representation for exporting sample is preferable；And when the survey of sample
The best curve that the chromatic value curve of colour appraisal mark color lump deviates corresponding comparison curve is more, but is in two acceptable limit songs
When within the scope of line, then show that the memory colour color representation for exporting sample is acceptable；With this, by the color of all typical memory colours
The overall color quality of quality characterization sRGB image output samples.
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