CN116778018A - Nonlinear color mapping method of depth map - Google Patents
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Abstract
The invention discloses a nonlinear color mapping method of a depth map, which comprises the following steps: reading data information of a depth map, wherein the data information of the depth map comprises pixel values of each pixel in the depth map; converting the depth map into a histogram according to the data information of the depth map; calculating a threshold value of the histogram; carrying out recombination processing on each bin interval of the histogram according to the threshold value to obtain a new bin interval combination; numbering the new bin intervals in sequence so that each new bin interval has a sequence number corresponding to one; calculating the sequence number of a new bin interval corresponding to the pixel value of each pixel in the depth map, and establishing a sequence number array of the depth map according to the calculation result; performing linear LUT color mapping on the sequence number array to obtain a color array after the nonlinear color mapping of the depth map, thereby completing the nonlinear color mapping of the depth map; the invention improves the visual effect by improving the utilization rate of the color gradation so as to increase the contrast of the image and the fullness of the color.
Description
Technical Field
The invention relates to the field of image and point cloud processing technicians, in particular to a nonlinear color mapping method of a depth map.
Background
The LUT is an abbreviation for LookUp Table, also known as a color look-up Table. In terms of image processing, the LUT can be used for achieving the effect similar to a filter, and the principle is that a mapping relation is essentially established, colors (R, G, B) or gray values are input, and the LUT is used for searching to obtain a new color (R, G, B) or gray value, so that one mapping operation is completed.
LUT color mapping methods are often used in the visualization of image processing to enhance the contrast of different levels of an image. Because the human eye recognizes colors much more than gray colors. The enhanced display method based on RGB color space usually uses warm color system color to represent large value and cold color system color to represent small value, which enhances the contrast of different layers of image and accords with the visual habit of people.
However, in the color mapping method in the prior art, linear mapping is generally adopted, and if the image data is not distributed uniformly enough, the mapped colors are more concentrated in a certain partial area, and other areas are rarely formed. This not only reduces the utilization of the tone scale, resulting in reduced look and feel, but also tends to mask the region of interest such that the image features are not noticeable.
Disclosure of Invention
The invention aims to provide a nonlinear color mapping method of a depth map, which improves the visual effect by improving the utilization rate of color gradation to increase the contrast of an image and the fullness of colors; on the other hand, the whole process does not need to provide an additional judging means, and the nonlinear color mapping can be adaptively completed only according to the data information of the depth map; in yet another aspect, the method can be used for data non-uniform distribution and data uniform distribution depth map, and has wide application range and strong adaptability.
In order to achieve the above object, the present invention discloses a nonlinear color mapping method for a depth map, which includes the following steps:
s1, reading data information of a depth map, wherein the data information of the depth map comprises pixel values of each pixel in the depth map;
s2, converting the depth map into a histogram according to the data information of the depth map, wherein the horizontal axis coordinate of the histogram represents the interval size of a bin interval, the vertical axis coordinate represents the number of corresponding pixels with pixel values falling in the bin interval, and the pixel value of each pixel of the depth map falls in the corresponding bin interval;
s3, calculating a threshold value of the histogram;
s4, carrying out recombination processing on each bin interval of the histogram according to the threshold value so as to obtain a new bin interval combination;
s5, numbering the new bin intervals in sequence so that each new bin interval has a one-to-one corresponding serial number;
s6, calculating the sequence number of a new bin interval corresponding to the pixel value of each pixel in the depth map, and establishing a sequence number array of the depth map according to the calculation result;
s7, performing linear LUT color mapping on the sequence number array to obtain a color array after the nonlinear color mapping of the depth map, thereby completing the nonlinear color mapping of the depth map.
Preferably, the histogram has a bin bins, the starting point value of the transverse coordinate of the histogram is M, the end point value is M, all bin bins are sequentially arranged in the range of [ M, M ] bins of the transverse coordinate of the histogram, and the width of each bin in the transverse coordinate of the histogram is w.
Preferably, the starting point value m of the transverse coordinate of the histogram is the minimum pixel value in all pixels in the depth map;
the end point value M of the transverse coordinates of the histogram is the maximum pixel value in all pixels in the depth map;
the width w of the bin in the transverse coordinate of the histogram is the average value of the difference value between the end value M and the start value M of the transverse coordinate of the histogram under a bin.
Specifically, the end point value M of the lateral coordinate of the histogram is calculated according to the formula m=max (H s :H e ) Calculated, the starting point value m of the transverse coordinates of the histogram is calculated according to the formula m=min (H s :H e ) The width w of the bin interval at the transverse coordinate of the histogram is calculated according to a formula w= (M-M)/(a), wherein H s For the pixel value of the starting pixel of the depth map, H e Is the pixel value of the endpoint pixel of the depth map.
Preferably, the step S3 specifically includes:
s31, sorting all the bin intervals in a descending order according to the number of pixels of each bin interval so as to obtain a current temporary bin interval combination;
s32, sequentially calculating the number of to-be-split bin intervals in the current temporary bin interval combination, accumulating the number of to-be-split bins until the accumulated value is equal to or closest to a, and recording the number of pixels corresponding to the bin intervals at the moment as a threshold value of the histogram.
Preferably, according to the formulaCalculating the number of splitting intervals of each bin interval in the current temporary bin interval combination, and counting the sum of the number of splitting intervals of all bin intervals in the current temporary bin interval combination;
wherein x is the number of pixels of any bin in the current temporary bin combination, z is the total number of pixels of all bins in the current temporary bin combination, mathematical symbol [ ] is the numerical value in logarithmic symbol [ ] is rounded down, and y is the sum of the number of intervals to be split of all bins in the current temporary bin combination.
Preferably, the step S4 specifically includes:
s41, calculating the difference value between the pixel number of each bin interval in the histogram and a threshold value;
s42, if the difference value between the pixel number of any bin in the histogram and the threshold value is greater than or equal to zero, splitting the current bin in the histogram into at least one new bin;
s43, if the difference value between the pixel number of any bin in the histogram and the threshold value is smaller than zero, discarding the current bin, and merging the bin range of the current bin and the number of pixels in the current bin into the previous bin.
Preferably, the step S42 specifically includes:
s421, if the difference value between the pixel number of any bin interval in the histogram and the threshold value is equal to zero, reserving the current bin interval;
s422, if the difference value between the number of pixels of any bin in the histogram and the threshold value is greater than zero, splitting the current bin in the histogram into at least two new bin intervals, wherein the number of pixels of the at least two new bin intervals is equal or close.
Preferably, the step S6 specifically includes:
according to the formulaCalculating the sequence number of new bin interval corresponding to the pixel value of each pixel in the depth map, and establishing the sequence number array of the depth map, wherein the mathematical symbol []Is a logarithmic sign []The numerical value in the histogram is rounded downwards, the mathematical symbol is a multiplier, H (i) is the pixel value of the ith pixel of the depth map, c is the c-th bin of H (i) in the depth map, K (c) is the bin splitting number before the c-th bin in the histogram, Q (c) is the bin splitting number of the c-th bin in the histogram, and n is the number of the new bin in which H (i) is located in the new bin combination.
Preferably, the nonlinear color mapping method of the depth map is operated in a multithreaded manner through an Intel TBB library.
Compared with the prior art, the method has the advantages that the histogram of the depth map is constructed, and each bin interval of the histogram is subjected to recombination processing to establish the nonlinear color mapping of the depth map, on one hand, the utilization rate of the color gradation is improved to increase the contrast ratio of the image and the fullness of the color, and the visual effect is improved, and on the other hand, the whole process of the method does not need to provide an additional judging means, and the nonlinear color mapping can be adaptively completed only according to the data information of the depth map; in still another aspect, the invention can be used for non-uniformly distributed data and depth maps of uniform distribution of data, and has wide application range and strong adaptability.
Drawings
FIG. 1 is a flow chart diagram of a non-linear color mapping method of the depth map of the present invention;
FIG. 2 is a histogram obtained in step S2 of the present invention;
FIG. 3 is a diagram showing the relationship between the histogram obtained in step S3 and the threshold value;
FIG. 4 is a diagram showing the relationship between the new bin in step S4 and the original bin in the histogram according to the present invention;
fig. 5 is a pair of comparison diagrams of a picture (left) obtained by a conventional linear mapping method and a picture (right) obtained by a non-linear color mapping method of a depth map;
fig. 6 is a further comparison of a picture (left) obtained using a conventional linear mapping method and a picture (right) obtained by a non-linear color mapping method of a depth map.
Detailed Description
In order to describe the technical content, the constructional features, the achieved objects and effects of the present invention in detail, the following description is made in connection with the embodiments and the accompanying drawings.
Referring to fig. 1-5, the nonlinear color mapping method of the depth map of the present embodiment is applicable to depth maps with data being unevenly distributed and data being evenly distributed, and includes the following steps:
s1, reading data information of a depth map, wherein the data information of the depth map comprises pixel values of each pixel in the depth map.
S2, converting the depth map into a histogram according to the data information of the depth map, wherein the horizontal axis coordinate of the histogram represents the interval size of a bin interval, the vertical axis coordinate represents the number of corresponding pixels with pixel values falling in the bin interval, and the pixel value of each pixel of the depth map falls in the corresponding bin interval.
Preferably, the histogram has a bin bins, the starting point value of the transverse coordinate of the histogram is M, the end point value is M, all bin bins are sequentially arranged in the range of [ M, M ] bins of the transverse coordinate of the histogram, and the width of each bin in the transverse coordinate of the histogram is w.
In this embodiment, the depth map is mapped to a picture with 256 color levels, that is, the value of a is 256, where the picture with 256 color levels may be a color map of (R, G, B) type, or a gray scale map, and of course, may be other types of color maps, and the specific picture type obtained by mapping is not limited herein. The number of gradation steps may be 4096, 65536, or the like, and is not particularly limited here.
Preferably, the starting point value m of the lateral coordinate of the histogram is the smallest pixel value among all pixels in the depth map. Specifically, the starting point value m of the lateral coordinate of the histogram is calculated according to the formula m=min (H s :H e ) And (5) calculating to obtain the product.
The end point value M of the lateral coordinate of the histogram is the largest pixel value among all pixels within the depth map. Specifically, the end point value M of the lateral coordinate of the histogram is calculated according to the formula m=max (H s :H e ) And (5) calculating to obtain the product.
The width w of the bin in the transverse coordinate of the histogram is the average value of the difference value between the end value M and the start value M of the transverse coordinate of the histogram under a bin. Specifically, the width w of the bin section at the transverse coordinate of the histogram is calculated according to the formula w= (M-M)/(a), that is, the formula w= (M-M)/(a) means that the range of the bin section of the transverse coordinate of the histogram is equally divided into a-parts of bin sections, and at this time, the width of each part of bin section is equal, that is, the bin section division of the histogram is linear.
Wherein,,H s for the pixel value of the starting pixel of the depth map, H e Is the pixel value of the endpoint pixel of the depth map. It will be appreciated that the depth map has a plurality of sequentially ordered pixels, the position of any one pixel on the depth map can be determined by ordering, and here H s For the first pixel of the depth map (i.e. H s Is the start of the depth map), while H e For the last pixel of the depth map (i.e. H e Is the end point of the depth map).
For convenience of illustration, each drawing of the present embodiment shows only the first ten of 256 bin bins, and in addition, gaps exist between bin bins of the histogram in the drawing, and gaps do not exist between bin bins of the actual histogram. In the drawing, minValue is M, and maxValue is M.
S3, calculating the threshold value of the histogram.
Preferably, the step S3 specifically includes:
s31, sorting all the bin intervals in a descending order according to the number of pixels of each bin interval so as to obtain a current temporary bin interval combination;
s32, sequentially calculating the number of to-be-split bin intervals in the current temporary bin interval combination, accumulating the number of to-be-split bins until the accumulated value is equal to or closest to a, and recording the number of pixels corresponding to the bin intervals at the moment as a threshold value of the histogram.
For example, the first 10 bins of the temporary bin interval are split into 25 bins respectively, the accumulated value is 250 at this time, the 11 th bin is split into 5 bins, the accumulated value becomes 255, at this time, the accumulated value is closest to a, if the twelfth bin is split, the accumulated value exceeds a, and the corresponding pixel number of the eleventh bin is the threshold.
It can be understood that, each time step S31 and step S32 are repeated, the total number of splitting intervals of all the bin intervals in the temporary bin interval combination is larger than the total number of splitting intervals of all the bin intervals in the previous temporary bin interval combination, so that the total number of splitting intervals approaches or equals to a after repeated times, thereby meeting the requirement of the preset number (a) of color levels. The threshold here serves in a subsequent step to split the histogram.
Preferably, according to the formulaCalculating the number of splitting intervals of each bin interval in the current temporary bin interval combination, and counting the sum of the number of splitting intervals of all bin intervals in the current temporary bin interval combination;
wherein x is the number of pixels of any bin in the current temporary bin combination, z is the total number of pixels of all bins in the current temporary bin combination, mathematical symbol [ ] is the numerical value in logarithmic symbol [ ] is rounded down, and y is the sum of the number of intervals to be split of all bins in the current temporary bin combination.
It can be understood that the above formula is performed by taking the number of the bin intervals as an integer and rounding down each time the number of the bin intervals is to be split.
S4, carrying out recombination processing on each bin interval of the histogram according to the threshold value to obtain a new bin interval combination so as to obtain nonlinear bin interval division.
Preferably, the step S4 specifically includes:
s41, calculating the difference value between the pixel number of each bin interval in the histogram and a threshold value.
S42, if the difference value between the pixel number of any bin in the histogram and the threshold value is greater than or equal to zero, splitting the current bin in the histogram into at least one new bin.
S43, if the difference value between the pixel number of any bin in the histogram and the threshold value is smaller than zero, discarding the current bin, and merging the bin range of the current bin and the number of pixels in the current bin into the previous bin.
Preferably, the step S42 specifically includes:
s421, if the difference value between the pixel number of any bin interval in the histogram and the threshold value is equal to zero, reserving the current bin interval.
S422, if the difference value between the number of pixels of any bin in the histogram and the threshold value is greater than zero, splitting the current bin in the histogram into at least two new bin intervals, wherein the number of pixels of the at least two new bin intervals is equal or close. It can be understood that, in general, more incremental thresholds are set, and after the number of pixels in any bin in the histogram exceeds the threshold, more splitting is performed according to the incremental threshold portion corresponding to the excess portion, which is not described herein. At this time, the range of the new bin range is changed, and the widths thereof are not necessarily equal, so that the nonlinear idea of the present embodiment is presented.
S5, numbering the new bin intervals in sequence so that each new bin interval has a corresponding sequence number. For 256 new bin intervals, the number of the first new bin interval is 0, the number of the tenth bin interval is 9, and the number of the 256 th bin interval is 255.
S6, calculating the sequence number of a new bin section corresponding to the pixel value of each pixel in the depth map, and establishing a sequence number array of the depth map according to the calculation result.
Preferably, the step S6 specifically includes:
according to the formulaCalculating the sequence number of new bin interval corresponding to the pixel value of each pixel in the depth map, and establishing the sequence number array of the depth map, wherein the mathematical symbol []Is a logarithmic sign []The numerical value in the histogram is rounded downwards, the mathematical symbol is a multiplier, H (i) is the pixel value of the ith pixel of the depth map, c is the c-th bin of H (i) in the depth map, K (c) is the bin splitting number before the c-th bin in the histogram, Q (c) is the bin splitting number of the c-th bin in the histogram, and n is the number of the new bin in which H (i) is located in the new bin combination.
S7, performing linear LUT color mapping on the sequence number array to obtain a color array after the nonlinear color mapping of the depth map, thereby completing the nonlinear color mapping of the depth map.
Preferably, the nonlinear color mapping method of the depth map is operated in a multithreaded manner through an Intel TBB library.
It can be understood that, in the nonlinear color mapping method of the depth map of the present embodiment, multiple traversal operations are required to be performed on the data information of the depth map, and such operations are very time-consuming for relatively large picture resources, so that in order to meet the requirement of industrial use, the present embodiment introduces an Intel TBB library, and increases the operation speed through multithreading.
The function applied to the Intel TBB library is mainly TBB, namely a parallel_for () function, and the specific formula is as follows:
Template<Typename Index,Typename Func>
Func parallel_for(Index first,Index last,[Index step,]const Func&f)。
referring to fig. 5 and 6, fig. 5 and 6 show respectively the contrast of the image (left) obtained by the conventional linear mapping method and the image (right) obtained by the nonlinear color mapping method of the depth map, and as can be seen from fig. 5 and 6, the contrast of the image obtained by the nonlinear color mapping method of the depth map of the present embodiment is high, the look and feel is good, and the emphasis of the image can be effectively highlighted.
1-6, the invention builds a histogram of the depth map, and carries out recombination processing on each bin interval of the histogram to build nonlinear color mapping of the depth map, on one hand, the invention increases the image contrast and the color fullness by increasing the utilization rate of the color gradation, and improves the visual effect, on the other hand, the whole process of the invention can adaptively complete the nonlinear color mapping only according to the data information of the depth map without providing an additional judging means; in still another aspect, the invention can be used for non-uniformly distributed data and depth maps of uniform distribution of data, and has wide application range and strong adaptability.
The foregoing description of the preferred embodiments of the present invention is not intended to limit the scope of the claims, which follow, as defined in the claims.
Claims (10)
1. A method for non-linear color mapping of a depth map, comprising the steps of:
reading data information of a depth map, wherein the data information of the depth map comprises pixel values of each pixel in the depth map;
converting the depth map into a histogram according to the data information of the depth map, wherein the horizontal axis coordinate of the histogram represents the interval size of a bin interval, the vertical axis coordinate represents the number of corresponding pixels with pixel values falling in the bin interval, and the pixel value of each pixel of the depth map falls in the corresponding bin interval;
calculating a threshold value of the histogram;
carrying out recombination processing on each bin interval of the histogram according to the threshold value to obtain a new bin interval combination;
numbering the new bin intervals in sequence so that each new bin interval has a sequence number corresponding to one;
calculating the sequence number of a new bin interval corresponding to the pixel value of each pixel in the depth map, and establishing a sequence number array of the depth map according to the calculation result;
and performing linear LUT color mapping on the sequence number array to obtain a color array subjected to nonlinear color mapping of the depth map, thereby completing the nonlinear color mapping of the depth map.
2. The method of non-linear color mapping of a depth map according to claim 1, wherein the histogram has a bin bins, the horizontal coordinates of the histogram have a start point value of M and an end point value of M, all bin bins are sequentially arranged within [ M, M ] bins of the horizontal coordinates of the histogram, and each bin has a width w in the horizontal coordinates of the histogram.
3. The method of nonlinear color mapping of a depth map according to claim 2, wherein a starting value m of a lateral coordinate of the histogram is a minimum pixel value among all pixels within the depth map;
the end point value M of the transverse coordinates of the histogram is the maximum pixel value in all pixels in the depth map;
the width w of the bin in the transverse coordinate of the histogram is the average value of the difference value between the end value M and the start value M of the transverse coordinate of the histogram under a bin.
4. A non-linear color mapping method of a depth map according to claim 3, characterized in that the end point value M of the lateral coordinates of the histogram is calculated according to the formula M = MAX (H s :H e ) Calculated, the starting point value m of the transverse coordinates of the histogram is calculated according to the formula m=min (H s :H e ) The width w of the bin interval at the transverse coordinate of the histogram is calculated according to a formula w= (M-M)/(a), wherein H s For the pixel value of the starting pixel of the depth map, H e Is the pixel value of the endpoint pixel of the depth map.
5. The method for non-linear color mapping of a depth map according to claim 2, wherein said calculating the threshold of the histogram comprises:
according to the pixel number of each bin section, descending order sorting is carried out on all the bin sections so as to obtain the current temporary bin section combination;
and sequentially calculating the number of to-be-split of the bin intervals in the current temporary bin interval combination, accumulating the number of to-be-split until the accumulated value is equal to or closest to a, and recording the number of pixels corresponding to the bin intervals at the moment as the threshold value of the histogram.
6. The method of non-linear color mapping of depth maps of claim 2, wherein the formula is followed byCalculating the number of splitting intervals of each bin interval in the current temporary bin interval combination, and counting the sum of the number of splitting intervals of all bin intervals in the current temporary bin interval combination;
wherein x is the number of pixels of any bin in the current temporary bin combination, z is the total number of pixels of all bins in the current temporary bin combination, mathematical symbol [ ] is the numerical value in logarithmic symbol [ ] is rounded down, and y is the sum of the number of intervals to be split of all bins in the current temporary bin combination.
7. The method of non-linear color mapping of a depth map according to claim 1, wherein the reorganizing each bin of the histogram according to the threshold value to obtain a new bin combination specifically includes:
calculating the difference value between the pixel number of each bin interval in the histogram and a threshold value;
if the difference value between the number of pixels of any bin in the histogram and the threshold value is greater than or equal to zero, splitting the current bin in the histogram into at least one new bin;
if the difference value between the pixel number of any bin in the histogram and the threshold value is smaller than or equal to zero, discarding the current bin, and merging the bin range of the current bin and the number of pixels in the current bin into the previous bin.
8. The method of non-linear color mapping of a depth map according to claim 7, wherein if a difference between a number of pixels of any bin in the histogram and a threshold is greater than or equal to zero, splitting a current bin in the histogram into at least one new bin, specifically comprising:
if the difference value between the pixel number of any bin interval in the histogram and the threshold value is equal to zero, reserving the current bin interval;
if the difference value between the number of pixels of any bin interval in the histogram and the threshold value is greater than zero, splitting the current bin interval in the histogram into at least two new bin intervals, wherein the number of pixels of the at least two new bin intervals is equal or close to the number of pixels of the at least two new bin intervals.
9. The method of claim 1, wherein the calculating the sequence number of the new bin interval corresponding to the pixel value of each pixel in the depth map, and establishing the sequence number array of the depth map according to the calculation result, specifically comprises:
according to the formulaCalculating the sequence number of new bin interval corresponding to the pixel value of each pixel in the depth map, and establishing the sequence number array of the depth map, wherein the mathematical symbol []Is a logarithmic sign []The numerical value in the histogram is rounded downwards, the mathematical symbol is a multiplier, H (i) is the pixel value of the ith pixel of the depth map, c is the c-th bin of H (i) in the depth map, K (c) is the bin splitting number before the c-th bin in the histogram, Q (c) is the bin splitting number of the c-th bin in the histogram, and n is the number of the new bin in which H (i) is located in the new bin combination.
10. The method of non-linear color mapping of a depth map of claim 1, wherein the method of non-linear color mapping of a depth map is run in a multi-threaded manner through an Intel TBB library.
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