Color filter for digital sensor and method of adjustment of a photofinishing camera provided with such a filter.

[0001] la an adaptive color filter comprising color pixel columns and columns of white pixels for digital sensor matrix, and a method for such a filter setting in use by a camera photo finish.

[0002] in the context of the digital photograph, have long been known photosensitive sensors formed of a mosaic of pixels; the sensors the most used for digital cameras that use for example the CCD technology (stands for filler-Complementary) or CMOS (stands for the Complementary metal oxide in Semiconductor DS1985). To produce color images, digital sensors is applied to these color filters, which are also present in the form of an array of different colors, each of the colors being dedicated to a pixel of the sensor to which it overlaps. The color that should be associated with each pixel on the resulting image is then obtained by image processing algorithms.

[0003] un color filters most known and most used is the Bayer filter, which is the form most conventional filter the RGB (R for Per, [...] to say red, g for putting green, [...] to say green, and finally b for the blue, [...] to say blue, these three colors are the basic colors for obtaining any other by combining additive synthesis). Such a filter uses a basic pattern covering 4 pixel, and which is repeated over the entire surface of the sensor, with two green pixels in opposite corners complemented by a blue pixel and a red pixel.

[0004] un drawback of this type of color filter is a remarkable reduction of the associated digital sensor sensitivity due to the significant attenuation of the amount of light that reached it. In effect, a good portion of wavelengths being absorbed by the different filters. For these reasons, different variants of the Bayer filter have since been proposed, especially by replacing one of the two green pixels by a white pixel in order to improve the sensitivity of the sensor. The basic pattern modified is in this case also repeated on all the filter.

[0005] in the field of sports competitions, there are also known auxiliary devices timing based on recognition of images, most known as photo finish. Such systems allow an operator to distinguish contestants spanning a finish line by viewing images taken successively by a high resolution camera centered very accurately at the finish line. The analysis of the sequence of images, taken at successive instants and corresponding therefore to different timed time, determine on the deferred, but very quickly after the arrival, more accurate time of crossing the line of each competitor, e.g. at thousandths of a second and classify the contestants reliably.

[0006] the cameras used by type devices often include photo finish type CCD [...] sensors (most known under the acronym the LS-CCDs) whose flow rate for capturing images is even higher than usual CCD cameras, thereby enabling a time resolution of up to ten thousandth of a second. The first sensors utilized for such cameras showed a matrix structure very particular rod-shaped, [...] to say a single column of pixels aligned very accurately on the finish line. Now there is a trend to use standard two-dimensional matrix sensors, selecting the column aligned with the finish line can then be performed by software.

[0007] for such cameras photo finish the LS-CCD-equipped with sensors, the RGB filters mentioned can of course be employed for obtaining color images. However, these filters are not adapted to provide adequate quality in any type of race. In effect, for example in dependence upon the time of the contest running or weather conditions, the ambient brightness vary considerably, and thus alter greatly the quality of images. The same is true of considerations related to the type of stroke, which affect the speed of competitors based on the prints and as a result the shooting parameters, including exposure time.

[0008] il exists therefore a need for cameras photofinishing provided with color filters for digital sensors free from these known limitations.

[0009] un aim of the present invention is to provide a new type of color filter having properties adaptive optics, and a novel method of adjusting particularly convenient camera photo finish using this filter.

[0010] these aims are achieved by a color filter for digital sensor formed of a two-dimensional array of pixels, each pixel corresponding to a given color, the pixel array being formed of alternate first columns of color and of second columns of white pixels, characterized in that each first pixel column comprises a sequence of color pixel based repeated over the entire first column of color pixels, the base sequence of pixels comprising at least three pixels of three different colors.

[0011] these objects are also achieved by a method of adjusting a [...] camera comprising such a color filter, characterized in that it comprises the following steps:

- a first step of choosing a basic pattern having optical properties of sensitivity, resolution and color quality predefined depending on parameters of stroke;

a second selection step - software of a set of adjacent columns whose number corresponds to the width of said base pattern selected;

- a third step of centering assembly of adjacent columns on the finish line.

[0012] in particular embodiments of the invention are defined in the dependent claims.

[0013] un advantage of the present invention is to continuously optimize the optical properties of photos colors obtained by the filter proposed, any conditions of use.

[0014] un another advantage of the proposed solution is to allow a rapid and efficient implementation of optical parameters selected for filming, and in particular, according to a preferred embodiment wherein all adjustments are made by adjusting software, without requiring movement of the [...] camera itself as none of its degrees of freedom. Thus adjustments for alignment of the [...] camera with respect to the finish line can be performed once for all, filter settings being obtained solely by software processing. The final blocking of all degrees of freedom and the absence of physical manipulation of the [...] camera this considerably simplifies the adjustment operations while for accommodating a maximum of types of race possible.

[0015] examples for implementing the invention advantageous are indicated in the description and illustrated by Figures appended hereto in which:

fig. 1 illustrates a top view respectively of a camera [...] used within the context of the invention, aligned on an incoming line;

fig. 2 illustrates a schematic diagram of a filter according to a preferred embodiment of the invention, and different basic patterns that may be selected;

fig. 3 illustrates a block diagram the different steps of the method of adjustment of a [...] camera according to a preferred embodiment of the present invention.

[0016] la Figure 1 shows a block diagram of a camera photo finish used within the framework of the present invention. The camera photo finish 3, preferably the LS-CCD, is aligned on an incoming line 2 of a track 1 preferably comprising multiple lanes 10 in which evolve the different competitors. It should be noted that the example of an athletic track 1 is fully indicative and non-limiting, cameras photofinishing 3 can also be used in a racing cyclists, of track motor races, or for horse racing.

[0017] la camera photo finish 3 preferably comprises 4 degrees of freedom, three in rotation and in translation. Figure 1 on, only the degree of freedom in translation T and a first degree of rotational freedom r1 about a vertical axis are illustrated; however the camera is preferably mounted for rotation about a ball 8 that simultaneously has second and third degrees of freedom in rotation of R2, R3 in order to handle the additional alignment of the optical axis of the camera 4 3 on the finish line 2. the camera photo finish 3 comprises a digital sensor 6 formed of a matrix of pixels, as well as a device for processing images 7 9 providing a digital signal output corresponding to the image sensed by the sensor. To form color images, the camera photo finish 3 further comprises a color filter 60 particular whose optical properties can be adjusted according to different predefined parameters, discussed farther. According to a preferred embodiment, this color filter 60 is affixed directly on the pixels of the digital sensor 6, so that by abuse of language being spoken of pixels also for the filter for naming the different colors covering a pixel of the digital sensor 6.

[0018] un such color filter 60 so that patterns of pixels corresponds to a preferred embodiment of the invention is illustrated in fig. 2. the width 61 62 and the overall height of the filter become counts in rows and columns of pixels, which are generally between 1024 and 2048 pixel. It is appreciated that the filter 60 is formed of alternating first columns of color pixels 611 and 612 of second columns of W of white pixels, each first column 611 is juxtaposed a second column 612. Such a configuration of a color filter 60 by columns is particularly suitable for a camera photo finish which uses only at most a few columns of pixels aligned on the finish line to allow a time stamp of the highest accuracy possible by associating these columns at a given time, while maximizing the size of the picture, the height of which is precisely determined by the number of pixels of the column.

[0019] each of the first columns of pixels 611 includes a base sequence comprising at least 3 different colors, in order to ensure good quality color picture obtained by additive synthesis based only on it and in not requiring any other pixel of another column. According to the preferred embodiment illustrated, each first column 611 pixel colors thus comprises at least one b-blue pixel, a green pixel g and a red pixel R however, alternatively, the colors used could also consist of cyan, magenta and yellow.

[0020] in Figure. 2, the base sequence is identical for each first column 611, i.e. the succession, from the top downward, of exactly three pixels: a first red R, green G a second, and a third blue B this sequence RGB is therefore repeated over the whole of each of the first columns color 611. The by utilizing only three pixels by sequence improves the color quality of Q, which is modeled in the scope of this invention as being inversely proportional to the number of pixel lines necessary to obtain color picture, as will be explained further in detail in connection with fig. 3. alternatively, could however use a sequence corresponding to a modified Bayer pattern wherein the base sequence repeated on each first column 611 would be the succession of four pixels instead of three, namely: a green G, a blue B, then another green g and finally a red R a variant base sequence would be advantageous in terms of sensitivity, because the color green is not as absorbent that blue and red. However, such improvement is done at the expense of quality color, since should be used 4 pixel lines instead of three. Furthermore, the fact of having identical sequences for each base sequence of each column may reduce the number of columns required to form the basic patterns, and thus to maximize the resolution of the picture.

[0021] as seen in Figure. 2, the arrangement of base sequences has is however not exactly identical for each first column 611 of color pixels. Indeed noticeable that each row of pixels has the same sequence pattern of pixels formed of a red R, green G a, then a blue, as for each first column 611 pixel color, with simply the white pixels of W interposed. such symmetry properties are obtained due to the offset of each base sequence in a height of a pixel of a first column 61 of color pixels to the next. In other words, if for a given pixel line, the pixel of a first column of color pixels 611 is of a certain color, e.g. red, the pixel of the same color will preferentially be located for example made by higher or lower, on the first column of pixels 611 following line and a lowest - or respectively more loud on the first column of pixels 611 of previous color. According to the preferred embodiment illustrated - see on the right of Figure 2 - the base sequences are offset by one pixel upward by scanning the columns of color pixel one by one from left to right. Therefore only the first columns of color pixels 611 "modulus 3" are exactly the same, by taking a formulation arithmetic, [...] to say that only the first, fourth, seventh, tenth and so on first columns 611 color pixel are identical, as are the second, fifth, eighth and so on and the third, sixth, ninth, like it is the reason that dotted lines have been traced for materializing a demarcation line dummy of exact replication of the pattern of 6 columns which is actually repeated on the entire filter 60. Advantageous optical properties of such offsetting base sequences has have been empirically checked with respect to filters for which all of the rows are identical color. In effect, in addition to considerations of symmetry evident lines with respect to the columns on the entire color filter 60, such an arrangement facilitates determination of color for each pixel by algorithmic calculation.

[0022] a using the color filter shown in fig. 60. 2, it is possible to take pictures in black and white, when for example the brightness is so limited that it is impossible to imagine a picture taken in color, using only a second column 612 of white pixels W-centered on the finish line. The filter 60 may list however different patterns to gradually adjust for different frame rates, conditioning the recordings and therefore the exposure time, and more exactly four basic patterns by determining different sensitivities, extending over a number of columns of between 1 and 3 and comprising respectively, 0.1 second or 2 of W columns of white pixels.

[0023] the four basic patterns Μ 1., 2. Μ, Μ 3 and m4 herein contain a number of pixels that is a multiple of three, corresponding to the three color pixels respectively red R, green g and blue b and which are systematically used. Thus each of these patterns extends over a height L of three pixels 3, while the width, equal to the number of pixels, is variable; the setting of the pattern width influences the resolution and parallel the sensitivity of the sensor. The detail of each of the four units of preferred illustrated is given below:

- the first base pattern m1 consists of exactly three pixels, and corresponds to the base sequence has a pixel red R, a green pixel g and a blue pixel b the first width of the first pattern n1 m1 is therefore equal to 1 pel, [...] to say that the first pattern m1 extends only over a single column;

- the second base pattern m2 consists of a matrix of 2 * 3=6 pixels containing the same base sequence has, red R of a pixel, a green pixel g and a pixel blue B, to which has been added a series of 3 W white pixels the second width of the second pattern n2 m2 is therefore equal to 2 pixel, [...] to say that this second pattern m2 extends on two columns including a first column 611 of color pixels and a second column of white pixels 612 of W;

- the third base pattern m3 consists of a matrix of pixels containing 3 * 3=9 two times three red R pixel, a green pixel g and a blue pixel b on first two adjacent 611, and a series of white pixels 3 W of a second column 612 interposed. The third width of the third pattern n3 m3 is therefore equal to 3 pixel, [...] to say that this second pattern extends over three columns m3, namely first two lanes of color pixels 611 and a second column of white pixels 612 of W;

- the fourth base pattern m4 is also formed of a matrix of pixel 3 * 3=9, but containing only a base sequence of three pixels: a red R, a green pixel g and a blue pixel b on a first columns 611, and this time two series of white pixels 3 W of two second columns adjacent 612. The fourth width of the fourth pattern n4 m4 is therefore always equal to 3 pixel.

[0024] the optical properties obtained with each of the basic patterns are conditioned, inter alia, 3 by the following parameters:

- s-sensitivity, which is modeled, in context of the present invention, as corresponding to the amount of light average per pixel, with an amount of 20% available per pixel blue B, 30% per pixel red R, green pixel g and 50% by 100% by white pixel W thus is strongly influenced on the one hand by the number of white pixels of W, and secondly by the number of respective pixels of P1, P3, and P3, P4 in, each pattern m1-to-m4, by which the overall sensitivity on all the pixels of the filter is divided. The extreme sensitivities are thus the first base pattern (worst) m1 and that of the fourth base pattern (the best);

- q-color quality, which is modeled in the scope of this invention as inversely proportional to the number of lines of the pattern, needed to complete the calculation of the color of each pixel by image processing algorithms. For the different basic patterns used, see that the best quality color Q is fixed because the height of each base pattern m1 to m4 is always equal to 3 pixel;

- and resolves, which is modeled as being equal to the number of columns n of each base pattern. Thus the resolution will be better at a finish line 2 that the respective number of columns of each pattern n1-to-n4 base is restricted. Thus the best resolution will be provided by the first pattern M1 base, while it will be worse for the third and fourth basic patterns of M3, m4.

[0025] to assess overall optical performances of each pattern, it will preferably multiply the scores for each of the sensitivity parameters S, Q of quality color, and n resolution above; however the choice of pattern will be performed considering a weight possible, especially on the sensitivity parameter sec. the value of the parameter Q being preferably attached, sought therefore preferably tradeoff between parameters S sensitivity and n resolution.

[0026] on appreciated that on all four patterns illustrated, at least three basic patterns comprise a different number of white pixels of W, namely 0.3 or 6 (respectively corresponding to the first pattern M1 base, to the second and third basic patterns m2-to-m3, and finally the fourth base pattern m4). This adjusts the sensitivity to at least three distinct levels (large-and-medium-low). Furthermore, the fact that the ratio of white pixels and the pixels of the colors may be respectively of 0% (for the first base pattern m1), 33% (for the third base pattern m3), 50% (for the second base pattern m2), and 66% (for the fourth base pattern m4) to further refine the granularity and the panel of choice of possible adjustments for this sensitivity parameter e, thereby accommodating for a large number of type of strokes and possible weather conditions, including typically a clear weather, a time warp, a time very cloudy and dark conditions. Finally, the fact that each of the basic patterns m1-to-m4 extends at least on 3 columns maintains a correct n resolution for the resulting image.

[0027] au bottom of the fig. 2 are referenced various sets of columns that may be selected in accordance with the pattern of selected base relatively to the racing state, [...] to say particularly brightness and the type of stroke a conditioning inter alia the passing speed of competitors at the finish line. Thus distinguished:

- a first set of columns corresponding to the first pattern c1 m1 base formed of a single column. Only three different like capability are illustrated on Figure 2 for questions of readability, but it will be appreciated that it is possible to use any first column 611 of color pixels;

- a second set of columns corresponding to the second pattern c2 M2 of base, formed of two columns, selectable indifferently on the entire sensor. For questions of readability, only five like capability have nevertheless been represented in Figure. 2;

- a third set of columns corresponding to the third pattern c3 base the M3, formed of 3 columns, two columns of pixels whose color (the. first columns 611) and a column of white pixels of W (i. e. a second column 612). Again, though only two like capability have been represented for a subset of 6 columns of the color filter 60, it will be appreciated that the selectable indifferently such an arrangement of two columns of color pixel with a column of white pixels interposed anywhere on the pixel matrix of the color filter 60;

- a fourth set of columns corresponding to the fourth c4 base pattern the M4, which is likewise formed of 3 columns, but which this time two columns of white pixels of W (i. e. chains of the 612) for a single column of color pixels (i. e. first columns 611). It is somewhat of a complementary set at third set of columns 3, the proportions of columns color and white columns are reversed. Again, though only two like capability have been represented for a subset of 6 columns of the color filter 60, it will be appreciated that the selectable indifferently such an arrangement of two columns of white pixels W with a column of color pixels interposed anywhere on the pixel matrix of the color filter 60.

[0028] on can therefore determining on the one hand that the determination of the number of columns corresponding to each n1-to-n4 base pattern m1-to-m4 does not systematically automatically select the correct set of columns to be c1-to-c4 aligned on the finish line 2 to provide the desired optical properties. For example, the third and fourth basic patterns m3 m4 and extend over an identical number of 3 columns (i.e. polyethoxylated was Ν 3. Ν==4. 3.) but have different optical properties. In this case, manipulation software shift might be needed, as will be explained below with the aid of fig. 3 that illustrates a sequence of steps for setting a [...] camera 3 according to a preferred embodiment of the invention, and more particularly focused on the basic patterns of the filter illustrated on Figure 2.

[0029] on the diagram of fig.. 3, the first step consists in choosing a e1 basic pattern having optical properties of sensitivity e, quality color Q and n resolution predetermined as a function of race parameters such as weather conditions and the type of stroke (the running speed of the number of lines of pixels per second that can range 1000 lines per second for athletics to more than 10000 lines per second for car racing, speed racing cyclists and horse being of the order of 3000 lines per second). According to the preferred embodiment of using the color filter of the fig.. 2, the quality parameter color is fixed because all basic patterns have a height L of 3 pixel.

[0030] during the second step the E2, determining a number of columns n corresponding to the desired pattern, and software selects a corresponding number of adjacent columns on the matrix. For the first base pattern m1 is therefore will select a first number of a single column n1, for the second base pattern is intended to identify a second number m2 n2 of two adjacent columns, and for the third and fourth patterns m3 and m4 is will select 3 adjacent columns (the third and fourth numbers n3 and n4 being equal, each respectively to 3).

[0031] then, a third step e3 centering of the set of adjacent columns obtained on the finish line 2 is performed. According to a preferred embodiment, emphasis throughout single handling software, such that some physical movement of the [...] camera 3, relatively tedious, is not ever required once it has been installed. As alternative, it may be physically moving the camera using inverse kinematic algorithms for optimizing the handling and minimize the amplitude of the movements in the various degrees of freedom among the three rotational axes r1.r2, r3 and the degrees of freedom in translation t1. To facilitate this step of centering, it is done in software only or not, may be used provided using a reticle auxiliary, as in the solution proposed in Patent ep0898249. When the number of columns is odd, aligning the central column on the finish line 2; when the number of columns is even, the operation is slightly more delicate one because it ideally placing the reticle between two adjacent columns. When a reticle auxiliary is used, it will be considered in practice that the third step e3 centering is terminated when the reticle is aligned with one of the columns of all of the columns selected.

[0032] on will however noted that when the number of columns of the selected pattern is odd, the centering of a set of adjacent columns of pixels equal to the width of the pattern does not necessarily ensuring that the correct set of columns, here the third and fourth set of columns for patterns and c4 c3 m3 and respectively the M4, has expired. Indeed, by choosing any column of pixels of the matrix of the filter, the likelihood of selecting a first column 611 of color pixels is the same as for selecting a second column 612 of white pixels of W, and similarly, by choosing a set of three adjacent columns of pixels, it is equiprobable that the set contains a single column of pixels white W on the three columns or 2 columns of white pixels. In this case, a fourth step E4, subsidiary and used only for a number n of odd columns ([...] i.e. equal to 2p + 1, P corresponding to a mathematical modeling of the divisor of the even number immediately below), offsetting the tubing assembly adjacent aligned on the finish line of a single pixel, [...] to say the equivalent of a column, to the left or to the right. Here it is easily seen that if a column of white pixels of W (i. e. a second column 612) is aligned on the finish line, only by shifting the reticle on the column immediately on its left or its right to be centered on a first column 611 of color pixels wherein provided the first base pattern at said third step m1 centering e3 for a first set of column c1 non-storage devices comprise more than one. And similarly, offsetting a set of three adjacent columns of a pixel to the right or to the left passes alternately of the third set of columns 3, corresponding to the third pattern m3 with 2 columns of color pixels, the fourth set of columns 4, corresponding to the fourth pattern m4 which one which contains more than one for every two columns of white pixels W when the number n of columns is even by against, [...] i.e. equal to 2p, the fourth step is never necessary.

[0033] therefore, adjustment using the method depicted in Figure 3 for a color filter 60 having the arrangement of first columns of color pixels 611, with basic patterns of R, gm, b., staggered, interleaved 612 of second columns of white pixels with W, see that the manipulations required for adjustment of the optical properties of the filter according to course conditions are extremely easy. Once the camera has been installed and that all its degrees of freedom have been permanently locked, one may choose a first pattern determining optical properties preferably corresponding to conditions of normal use, or statistically most likely. This pattern extending over 1 to 3 columns, eight seconds can select one or two additional columns at most, or respectively retract or deselect one or two at most, then shift, if necessary, the set of columns obtained from a single pixel width if the number of columns is odd. To further facilitate the operation of the centering, when these are accomplished by the use of a reticle auxiliary as in the solution proposed in Patent ep0898249 of the applicant, it shall be possible to choose to systematically select, default, the column of pixels on which the reticle is aligned and the complete if necessary by additional columns of pixels at the second step e2 prior selection software for a set of columns whose number is strictly greater than one. The manipulations remaining for centering are then extremely rough and can thus have a maximum reactivity, which is often essential for events taking place outdoors, thus highly exposed to changes in weather conditions, and in real-time as for example prints an athletic league during world or Olympic games.

[0034] the convenience of usage the rest of not only for initial settings of the camera system with regeneration, but also to dynamically adjust the optical properties of the color filter 60 by changing the selection of the base pattern. The by having only at most 2 columns to add or remove - respectively, according to the conditions - and does not need an offset that at most one pixel column width is all the more appreciable when the time endured over several periods of the day, for example prints an athletic for which the qualifications are accomplished in a day and the final often late in the evening or during the night. Thus for example if the first base pattern m1 is selected as a default for daytime use conditions, it suffices to add a second column 612 adjacent white pixel W to obtain the second base pattern the M2, of improved sensitivity, and a further second column 612 of white pixels W in the evening, so the two second columns of white pixels 612 W are respectively located on either side of the first column 611 of color pixels aligned on the finish line 2, to obtain the fourth base pattern the M4, whose sensitivity is even better, when the night fallen. And for adjusting the color filter on an intermediate susceptibility, if necessary, it will be possible to change from the first base pattern m1 at third base pattern of M3, by adding two adjacent columns, respectively a second columns of white pixels 612 W and a first column 611 of color pixels on the same side, and then by shifting the set of a pixel. All of this selection software simple addition and/or optionally de-select pixel columns can thereby allow follow a trip during its by adjusting an extent as possible and as the optical properties of the optical filter installed on the camera photo finish 3.

[0035] on will however that the basic patterns m1-to-m4 and the base sequence was just as an example to illustrate a particularly preferred embodiment. However, other basic patterns extending over a larger number of columns, or comprising a base sequence has extending over a larger number of pixels, or including other colors is also possible without departing from the scope of the invention, since the manipulation software centering and offset remain relatively simple. It will be possible for example in particular consider base sequences alternate R, gm, b., and cyan, a magenta, yellow on two successive columns.

[0036] further, without departing from the scope of the present invention, the method of adjusting a camera photo finish described above may also elect to use only any subset of patterns from the set of four patterns m1 to m4 above, based on the usage conditions, which require for example use only only two or three patterns on the four.