CN1925623A - Even method for luminance of mobile phone camera - Google Patents

Abstract

This invention discloses one cell phone cameral brightness evening method, which comprises the following steps: getting light intensity distribution parameters; measuring RGB brightness parameters of different light intensity to get one integral value; fitting curve on integral measurement values and light intensity distribution parameters to get light intensity parameters curve to determine light intensity correction values; realizing cell phone image light intensity even distribution according to correction values. This invention corrects the test and theory values to get even photos.

Description

A kind of even method for luminance of mobile phone camera

Technical field

The present invention relates to the mobile phone camera image processing techniques, relate in particular to a kind of even method for luminance of mobile phone camera.

Background technology

Along with mobile phone portability and picture element improve constantly, in some cases, as tourism, the more glad use mobile phone photograph of consumer.But existing low pixel mobile phone only can be used for satisfying general needs, though high-pixel mobile phone camera pixel reaches the low digital camera level that waits, photograph has tangible brightness disproportionation.

For subject (no matter be positioned at a distance or nearby), it can be considered as area source in theory, area source is imaged on CCD (Charge Coupled Device through camera lens, the charge-coupled device element) or on the CMOS (Complementary Metal Oxide Semiconductor, complementary metal oxide semiconductors (CMOS)).As shown in Figure 1, the light of subject a is imaged on the photosurface c through camera lens b.In theory, be of a size of infinity at a and b, and under the enough little condition of sensor devices c size, be the uniformly light-emitting face as a, c place luminance uniformity can reach＜5% (valuation), and human eye is difficult to differentiate.And in fact, the size of a, b all is limited, main is because the size of b is quite little, thus on c the brightness of image uniformity＞5%, tangible shade is arranged, can be referring to Fig. 2, a is actual CCD pixel faces, considers uniformly for picture brightness, cuts out and goes to a marginal portion, keep b as effective CCD pixel, just the sensitization part of the photograph of final output.C is the part of luminance uniformity＜5%, and human eye is insensitive to the Luminance Distribution inequality, and d is the part of luminance uniformity＞5%, and human eye is uneven responsive to Luminance Distribution.

The sensitivity speck of color camera is made up of RGB (red, green, blue) three primary colors, and each R, G, B have relevant register, are used for noting down the power of light, and then differentiates object color and brightness, imaging just, and pixel distribution is as shown in Figure 3.Area source is through aperture diaphragm and lens, because the effect of lens, the imaging light intensity is distributed as Bei Saier and distributes, and as shown in Figure 4, wherein, the z axle is represented light intensity, and x and y are reference axis.The decentre peak is far away more among the figure, and then brightness is more little, apart from the identical each point brightness unanimity of center apogee distance, because picture is a rectangle, so four jiaos of inevitable concentricity round regional luminance differences of place's brightness cause the photograph brightness disproportionation, influences picture element.

In order to overcome above-mentioned shortcoming, adopting usually in the prior art increases the CCD area to improve the method for even illuminating area.Referring to Fig. 2, increase a or reduce the area of b.The method increases cost, and still can not eliminate the shade at four jiaos of places of photograph.

Summary of the invention

The problem to be solved in the present invention provides a kind of even method for luminance of mobile phone camera, to solve the uneven defective of imaging surface brightness in the prior art.

In order to realize above purpose, one embodiment of the invention provide a kind of even method for luminance of mobile phone camera, may further comprise the steps:

A, obtain the light distribution parameter;

RGB brightness number under B, the measurement different light intensity obtains normalized measured value;

C, described normalized measured value and described light distribution parameter are carried out curve fitting, obtain the light intensity parameter curve, and then the corrected value of definite light intensity parameter;

D, realize that according to described corrected value the light intensity of image in the mobile phone camera evenly distributes.

Compared with prior art, the present invention has the following advantages:

The present invention pursues the pixel intensity correction according to test and theoretical value to actual photograph, obtain the photograph of good evenness, mobile phone camera for high pixel can reach the equal picture element level of low side digital camera, make unevenness＜5% of Luminance Distribution function in the imaging surface, as shown in Figure 5, wherein the z axle is a light intensity, and x axle and y axle are coordinate.

Description of drawings

Fig. 1 is prior art imaging optical path figure;

Fig. 2 is the prior art imaging surface surface of intensity distribution;

Fig. 3 is the prior art pixel map;

Fig. 4 is the prior art CCD surface of intensity distribution;

Fig. 5 is the CCD surface of intensity distribution of the present invention;

Fig. 6 is an even method for luminance of mobile phone camera flow chart of the present invention;

Fig. 7 is the index path that the present invention obtains the light distribution parameter;

Fig. 8 is user expectation CCD light intensity curve and Theoretical Calculation curved surface distribution map;

Fig. 9 is the difference of two curved surfaces among Fig. 8.

Embodiment

Even method for luminance of mobile phone camera of the present invention may further comprise the steps as shown in Figure 6:

Step s501 obtains the light distribution parameter.As shown in Figure 7, set of lenses comprises lens T ₁And T ₂, the set of lenses radius is r ₀, image device comprises CCD (or CMOS), and its radius is r, and the distance of set of lenses and image device is z.

According to the opinion of the real lens calculation of parameter CCD foliation among Bei Saier function and Fig. 7 normalization light distribution I, wherein, I=EE ^*

$E=(-\frac{i}{\mathrm{az}})e^{\mathrm{ikz}}\∫\∫T_1\·T_2\exp \left\{\frac{\mathrm{ik}}{2z}\right[{r_0}^2+r^2-2{\mathrm{rr}}_0\cos ({\mathrm{\θ}}_0-\mathrm{\θ})\left]\right\}{r}_0{\mathrm{dr}}_0{\mathrm{d\θ}}_0$

$T_1=\left\{\begin{array}{c}1(r_0<=a_0)\\ 0(r_0>a_0)\end{array}\right.$ T ₂With T ₁Value is identical, a ₀Be the diaphragm radius.

Then, it is poor to obtain the CCD each point according to light distribution, and this function is designated as F ' (A _x).

Above-mentioned function is carried out the normalization process: $F_1\left(A_1\right)=\frac{F_1^{\&prime;}\left(A_1\right)}{F_1^{\&prime;}\left(A_1\right)}=1,$ $F_2\left(A_2\right)=\frac{F_2^{\&prime;}\left(A_2\right)}{F_1^{\&prime;}\left(A_1\right)},......,$

$F_n\left(A_n\right)=\frac{F_n^{\&prime;}\left(A_n\right)}{F_1^{\&prime;}\left(A_1\right)}.$ CCD light intensity curve and Theoretical Calculation light distribution curved surface that Fig. 8 two curved surfaces are desired respectively, Fig. 9 is both differences.

Step s502 measures the RGB brightness number under the different light intensity, obtains normalized measured value;

At first, in the darkroom, prepare a red area source, take pictures with camera; Then prepare green and blue area source respectively, take pictures.Obtain each point RGB brightness number, the acquisition of numerical value can obtain from the mobile phone debugging software, with numerical value be designated as F1 ' (A1), F2 ' (A2) ..., Fn ' (An), traversal CCD all pixels.Wherein area source can adopt LCD, also can adopt other modes.

Then, adopt same batch of a plurality of sample cameras to test, the record numerical value, with results averaged, obtain F1 (A1), F2 (A2) ..., Fn (An).

At last, with the normalization as a result of above-mentioned mean value, obtain normalized measured value.

Step s503 carries out curve fitting the normalized measured value and the curve of light distribution, obtains the light intensity parameter curve of this CCD device, and then the corrected value of definite light intensity parameter.Can utilize Matlab software to carry out curve fitting.

When distance, can not provide enough big area source as test, nearly range points is carried out match, obtains far point numerical value, when light source leaves 1 meter, can be equal to the light source of infinite distant place; Work again carries out curve fitting.For different light intensity, but repeating step s502.CCD light intensity parameter curve (with lens group and CCD relating to parameters) under arrangement light intensity value and the corresponding light intensity; And calculated correction value, what corrected value was every some theoretical value with match value is poor.

Step s504 realizes that according to described corrected value the light intensity of handset image evenly distributes.At first, this corrected value is deposited in the mobile phone control unit, mobile phone can be called in corrected value numerical value in the register is revised according to different light intensity.Mobile phone generates the corresponding function of handling according to above-mentioned corrected value, carries out respective operations, for example, handles function and at first reads each pixel number certificate of CCD, with each point data and corrected value addition, obtains uniform light distribution then; Or, handle function and at first read each pixel number certificate of CCD, then each point data and weights are multiplied each other, obtain uniform light distribution.Wherein, weights are the relation of the multiple between theoretical value and actual value under each light intensity.

More than disclosed only be several specific embodiment of the present invention, still, the present invention is not limited thereto, any those skilled in the art can think variation all should fall into protection scope of the present invention.

Claims (6)

1, a kind of even method for luminance of mobile phone camera is characterized in that, may further comprise the steps:

A, obtain the light distribution parameter;

RGB brightness number under B, the measurement different light intensity obtains normalized measured value;

C, described normalized measured value and described light distribution parameter are carried out curve fitting, obtain the light intensity parameter curve, and then the corrected value of definite light intensity parameter;

D, realize that according to described corrected value the light intensity of image in the mobile phone camera evenly distributes.

2, even method for luminance of mobile phone camera according to claim 1 is characterized in that steps A further comprises:

A1, obtain the imaging surface light distribution according to Bei Saier function and lens parameters;

A2, normalization operation is carried out in described light distribution, obtained the light distribution parameter.

3, even method for luminance of mobile phone camera according to claim 1 is characterized in that step B further comprises:

Utilize red, green and blue area source respectively, collect imaging surface each point RGB brightness number,, obtain normalized measured value The above results normalization.

4, even method for luminance of mobile phone camera according to claim 1 is characterized in that step C carries out curve fitting by Matlab.

5, even method for luminance of mobile phone camera according to claim 1 is characterized in that step D specifically comprises: this corrected value is deposited in the mobile phone camera control unit, make mobile phone according to different light intensity, call in corrected value numerical value in the register is revised.

6, as even method for luminance of mobile phone camera as described in the claim 5, it is characterized in that step D further comprises:

Mobile phone camera generates according to corrected value and handles function;

Mobile phone camera reads each pixel number certificate in the register;

With described processing function described each pixel number certificate is handled, obtained uniform light distribution.

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