# Patent

## Title
Method and system for determining statistical data for image pixels having a higher bit depth per band

## Abstract

A system and method for determining statistical data within an image having pixels with relatively higher bit depth per band and a system and method of converting a first image within the image having pixels with the relatively higher bit depth per band into a second image having a relatively lower bit depth per band. The higher bit depth per band includes greater than 8 bits per band. The method of determining statistical data for pixels of an image includes dividing the image having pixels with the higher bit depth per band into a plurality of polygonal sections, each polygonal section including substantially homogenous features; computing statistical data for pixels within each polygonal section; and storing the statistical data with the image.

## Background
CROSS REFERENCE TO RELATED APPLICATION
The present patent application claims priority from provisional patent application No. 61/314,257 filed on Mar. 16, 2010, the contents of which are incorporated herein by reference.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to data management and in particular to a method and system for determining statistical data for pixels of an image and a method and system of converting an image for viewing on a display device.
2. Discussion of Related Art
An image generally contains a plurality of pixels and each pixel has one, two or more bands. Each band has a certain color depth or bit depth. For example, an RGB color-based image has 3 bands, the red band (R), the green band (G) and the blue band (B). Each of the R, G and B bands can have a depth of 8 bits or more. In order to be able to visualize or view images having a bit-depth greater than 8 bits per band (i.e., images having a depth of N-bits per band, with N greater than 8) on a display device that is configured to display an image having 3 bands (each band having an 8-bit depth), a bit depth down-sampling operation is performed. For example, a bit-depth down-sampling operation is performed on the image having N-bits per band to transform or convert the image into another image in the RGB system where each band (R band, G band and B band) has 8 bits of depth (i.e., a 24-bit RGB image).
Some conventional methods use a pre-computed N-bit to 8-bit look up table (LUT) per band to down-convert the image with higher bit depth per band into a lower bit depth (e.g., 8-bit depth) per band. When referring to “higher” bit depth per band herein, this is intended to refer to a bit depth of greater than 8 bits per band. Other methods such as tone mapping method involve executing algorithms to adaptively compute the N-bit (where N is greater than 8) to 8-bit conversion, pixel by pixel. The latter method of performing the down-conversion or down-sampling can be computer and time intensive based on the quality of the implementation of the algorithm. An increasing number of computing environments have implemented these two types of down-conversion methods into hardware or into software. Most of these methods employ the generation and application of statistical information gathered by processing pixel data in the image.
When pixels containing bands with bit depth greater than 8-bits per band are stored into disk files, they are stored in 16-bit, 32-bit, or higher bit depths per band. For example, an original image sensor may have captured data at 10, 11, 12, or 15 bits per band. However, when an image file containing these pixel values is stored on disk, it is generally stored at 16-bits per band. While this may be considered as waste of space, it is also deemed highly efficient for computing platforms of today.
When a vendor distributes to a customer imagery that was originally captured at a value greater than 8 bits per band (e.g., 16-bits per band), very often the vendor is forced to distribute the original image data as well as additional image data that was pre-converted at significant computational cost to the 8-bit depth per band, specifically for display. Under these circumstances, the 8-bit data would occupy an additional 50% more storage alongside the original 16-bit data. Compression is further used to save space on disk. If the compression is lossy, the compression degrades the image. If the compression is not lossy, the compression is not as efficient to read and decode the compressed data for visualization. A customer sometimes may choose to discard the original 16-bit data and just use the 8-bit data in critical decision making tasks because of a lack of sufficient amount of storage or the lack of computing power to handle on-the-fly conversions. If the customer chooses to only use 16-bit data in critical decision making tasks, the overhead of on-the-fly conversion to 8-bit depth for visualization bears an additional computational cost or requires additional computing power which further increases costs. However, the flexibility that on-the-fly 16-bit to 8-bit depth conversion offers is that the customer can select one of several methods to convert the image to 8-bit depth prior to display.
If a computationally inexpensive method was available for better on-the-fly visualization of data that was collected and stored at bit depths greater than 8-bits per band, it would be ideal to supply the original data (greater than 8-bits per band) to the customer and let the customer choose amongst the various methods available for displaying this data. Hence, distributing pre-converted 8-bit depth per band data would not be necessary, thus saving additional disk space requirement as well as saving the vendor the added cost of converting the data to 8-bit depth.
The method or methods described in the following paragraphs provide a mechanism for pre-computing and storing data within the image, and utilizing this data to make subsequent on-the-fly conversion of the image data having a higher bit depth per band to a lower bit depth per band (e.g., 8 bit depth per band) for the display of the image computationally inexpensively.
BRIEF SUMMARY OF THE INVENTION
An aspect of the present invention is to provide a method for determining statistical data for pixels of an image, the pixels having a higher bit depth per band. The higher bit depth per band includes greater than 8 bits per band. The method includes dividing the image having pixels with the higher bit depth per band into a plurality of polygonal sections, each polygonal section including substantially homogenous features; computing statistical data for pixels within each polygonal section; and storing the statistical data with the image.
Another aspect of the present invention is to provide a system for determining statistical data for pixels of an image, the pixels having a higher bit depth per band. The higher bit depth per band includes greater than 8 bits per band. The system includes a processor configured to: (a) divide the image having pixels with the higher bit depth per band into a plurality of polygonal sections, each polygonal section including substantially homogenous features; (b) compute statistical data for pixels within each polygonal section; and (c) store the statistical data with the image.
Another aspect of the present invention is to provide a method of converting a first image within an image having pixels with a relatively higher bit depth per band into a second image having pixels with a relatively lower bit depth per band. The method includes selecting a first image, the first image corresponding to a viewport from an image having pixels with the higher bit depth per band, the image having pixels with the higher bit depth per band being divided into a plurality polygonal sections, each polygonal section including substantially homogenous features; and determining, for each pixel with the higher bit depth per band within the first image, to which polygonal section in the plurality of polygonal sections each pixel belongs to. The method further includes converting each pixel with the higher bit depth per band within the first image into a corresponding pixel of a lower bit depth per band using statistical data of a polygonal section to which each pixel belongs to; and forming the second image having pixels of the lower bit depth per band.
Yet another aspect of the present invention is to provide a system of converting a first image having a relatively higher bit depth per band into a second image having a relatively lower bit depth per band. The system includes a processor configured to: (a) select a first image, the first image corresponding to a viewport from an image having pixels with the higher bit depth per band, the image having pixels with the higher bit depth per band being divided into a plurality polygonal sections, each polygonal section including substantially homogenous features; (b) determine, for each pixel with the higher bit depth per band within the first image, to which polygonal section in the plurality of polygonal sections each pixel belongs to; (c) convert each pixel with the higher bit depth per band within the first image into a corresponding pixel of a lower bit depth per band using statistical data of a polygonal section to which each pixel belongs to; and (d) form the second image having pixels of the lower bit depth per band.
Although the various steps of the method are described in the above paragraphs as occurring in a certain order, the present application is not bound by the order in which the various steps occur. In fact, in alternative embodiments, the various steps can be executed in an order different from the order described above or otherwise herein.
These and other objects, features, and characteristics of the present invention, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. In one embodiment of the invention, the structural components illustrated herein are drawn to scale. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention. As used in the specification and in the claims, the singular form of “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.



BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 depicts the geographical map of the continental United States of America (CONUS) that is divided into visually homogenous regions or sections, according to an embodiment of the present invention;
FIG. 2A depicts a converted image from an unsigned 16 bits per band image using a conventional standard-deviation technique applied to the histogram of the whole image file;
FIG. 2B depicts the same image converted from unsigned 16 bits per band to an unsigned 8 bits per band image according to an embodiment of the present invention;
FIG. 2C depicts a polygonal layout (e.g., quadrilateral layout) used to sub-divide the image in FIG. 2B into a plurality of regions or sections; according to an embodiment of the present invention;
FIG. 3A depicts an image portion obtained when zooming into the top-left corner region of the image shown in FIG. 2A;
FIG. 3B depicts an image portion obtained when zooming into the top-left corner region of the image shown in FIG. 2B;
FIG. 4 is a representation of R-sets in relation to each other and in relation to the original image, according to an embodiment of the present invention;
FIG. 5 represents a hierarchical tree or relationship structure between various quads within an image, according to an embodiment of the present invention;
FIG. 6 depicts a structure for storing statistical data for the original image and each R-set, each divided into several regions, according to an embodiment of the present invention;
FIG. 7 is a flow chart depicting a method of pre-computing the statistical data used for converting a first image of higher bit depth to a second image of lower bit depth, according to an embodiment of the present invention; and
FIG. 8 is a flow chart depicting the method of converting a first image to a second image that can be displayed for a given area of interest (AOI) in the NUI file, using feature-based statistics and associated data generated earlier, according to an embodiment of the present invention.



DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
Some image files such as image files in the new universal image (NUI) file format implemented by PIXIA Corporation, can contain a relatively large number of pixels that can scale to over four billion (4×109) by four billion (4×109) pixel raster. NUI image files having a size of several million pixels wide by several million pixels tall can be found in many areas including geography, aerial and satellite images, medicine, etc. For example, images that cover many geographical areas such as cities, provinces, countries and continents can be as large as several million pixels by several million pixels. The NUI file format has the capacity of storing typical band layouts such as luminance, red-green-blue (RGB), near infrared (NIR), multi-spectral, hyper-spectral and ultra-spectral bands. The NUI file format can also be configured to store various bit-depths such as, but not limited to, unsigned 8 bits (u8), signed 16 bits (s16), unsigned 16 bits (u16), signed 32 bits (s32), unsigned 32 bits (u32), 32-bit floating point (f32), 64-bit double precision floating point (f64) and complex. In addition, within NUI files containing bands with signed 16-bit depth and unsigned 16-bit depth, the NUI file format can also carry between 9 and 15-bits per band image data. The NUI file format can store the image data uncompressed. Alternatively, the NUI file format can also store the image data as compressed. In one embodiment, the compression can be performed using a conventional JPEG2000 compression method.
The NUI file, as part of its format, stores statistical data about the image. This statistical data includes, but is not limited to, a histogram of each band of each pixel in the image, minimum, maximum value of each band of each pixel in the image, standard deviation, mean, median, mode, skew, and kurtosis of each band of each pixel in the image. In one embodiment, a display system or device can use the statistical data to generate a custom look-up table (LUT). Multiple LUTs may be generated using multiple techniques based on user's requirements. The LUT may be further used to convert pixels in the image containing bands of higher bit depth (e.g., bit depth greater than 8-bits per band) to an image containing bands of lower bit-depth (e.g., 8-bits per band) that can be displayed on, for example, a 24-bit RGB display device (i.e., a display device limited to an 8-bit depth per band).
The NUI file, as part of its format, stores in addition to the original image, a set of user-defined reduced resolution datasets (RRDs or R-sets). Each RRD is a smaller, zoomed-out version of a previous RRD and a first RRD is a smaller, zoomed-out version of the original image. The terms RRD and R-set are used herein interchangeably. FIG. 4 is a representation of R-sets in relation to each other and in relation to the original image, according to an embodiment of the present invention. As shown in FIG. 4, the first R-set is a zoomed-out version of the original image, the second R-set is a zoomed-out version of the first R-set, and the third R-set is a zoomed-out version of the second R-set, etc.
However, the use of the histogram for the entire NUI file, in particular when the NUI file is relatively large (e.g., a file containing imagery captured over a vast geographical region such as satellite or aerial imagery), may have a drawback. Indeed, as the number of populated pixels in the NUI file increases, the dynamic range of pixel band color values stored within the image data can increase considerably. For example, a large geographical area occupied by a country such as the United States of America, China, Russian Federation or India may cover various geographical features such as deserts, tropical forests, farmlands, snow capped or rocky mountain ranges, and densely populated cities. Therefore, a histogram obtained from such a diverse set and vast region of pixels would have a very broad distribution of color (e.g., golden, brownish, green, blue, etc.).
If such a diverse dynamic range of pixels is converted from higher bit-depths, for example from unsigned 16 bits (u16 bits) per band to unsigned 8 bits per band within a 3 band color scheme, a single u16 to u8 look-up table (LUT) may not have enough slots to represent all the visual features and the range of colors within these features.
The resulting converted image (converted from higher bit depths per band to lower bit depths per band) may look “washed out” or “faded” with every region losing detail so as to do distribute the limited color space to all other regions. This is generally rectified by applying further image processing methods such as a contrast curve or dithering to the converted image. Since the detail is already lost, the best this process can do is add additional artifacts that further remove detail but give the perception of greater image fidelity. For example, subtle gradations in clouds and snow covered regions of very rocky mountains may not show up and would look to the eye all white. This may not be desirable when implementing high dynamic range rendering (HDRR) and tone mapping to retain a high dynamic range image (HDRI). Hence, in order to remedy this deficiency, in one embodiment, a plurality of histograms can be generated and stored for geographical regions that contain reasonably homogeneous features.
In one embodiment, a geographically diverse region image such as a geographical image of United States of America can be divided into, for example, a plurality of polygonal image sections or regions (e.g., triangular sections, quadrilateral sections, pentagonal sections, hexagonal sections, etc., or any combination of two or more thereof) that have reasonably visually similar geographical features. Consider a geographically contiguous region. Also consider that when looking at this region from an elevated point (for example, of over 10,000 meters), the color-space of the region seems to be subjectively visually uniform (for example: a desert, a mountain range, or a tropical rain forest). In one embodiment, such a region can be considered as having reasonably similar features in the present context. Such a region can also be referred to as a relatively homogenous region in the present context. Histograms and LUTs can be computed for each of the plurality of polygonal image sections. One of the LUTs computed for a specific image section can be selected and applied to pixels that fall into that image section and having a higher bit-depth per band to transform each respective image section into a corresponding image section having a lower bit-depth per band that can be displayed or viewed on a display device. In other words, a specific look up table within the computed plurality of LUTs that is associated with the polygonal section to which a pixel with the higher bit depth per band belongs to can be selected and used to transform the pixel having the higher bit depth per band into a pixel having a lower bit-depth per band that can be displayed or viewed on a display device. A LUT generated by using the overall image histogram can be applied to pixels that fall in sections outside of any of the polygonal image sections having the features. However, the LUT generated by using the overall image histogram may not be needed if each pixel in the image falls within at least one specific polygonal section containing a feature. In other words, the LUT generated by using the overall image histogram may not be needed if substantially the entire image is divided into polygonal sections for which a specific LUT can be calculated.
For instance, for a given NUI image or R-set, the NUI can be divided into R distinct relatively homogenous regions. For each specific relatively homogenous region Rs (i.e., for each region having relatively homogeneous features), an entry Es can be computed. The entry Es is an abstract object that contains all statistical and polygonal data to associate Es with a corresponding region Rs.
In one embodiment, the polygonal sections can be quadrilateral sections. In one embodiment, an entry Es of each quadrilateral section in the plurality of quadrilateral sections contains: (a) a single quadrilateral (quad) Qs. The quad Qs is defined, for example, as a closely convex quadrilateral in pixel space to cover a region Rs that is reasonably homogenous with respect to its visual features Fs. In one embodiment, the selection of the quadrilateral sections or regions having the homogenous features in the image can be accomplished manually by selecting manually each quadrilateral region or section in the image based on the perception of a user. In another embodiment, the selection of the quadrilateral sections can be accomplished automatically using methods or algorithms (implemented by hardware or software) that can detect various homogenous features and thus delimit the various homogenous features by quadrilaterals to define the quadrilateral sections.
In one embodiment, the entry Es further contains (b) statistical data, for example in the form of a histogram Hs for all pixels within the quadrilateral Qs. The histogram Hs is computed and stored for each band in each pixel within the homogenous quad Qs section. In one embodiment, pixels on the boundaries of each quadrilateral section Qs can be included within the quadrilateral sections so as to eliminate, for example, sub-pixel errors or lost pixel issues. The relative homogeneity of each quadrilateral region or section is substantially not affected by the addition of the boundary pixels. The time ts at which Hs was generated is also stored.
In one embodiment, the statistical data may further include, optionally, (c) a plurality of N computed LUTs, i.e., N LUTs L[N]s, where N is selected between zero and Nmax (i.e., 0<N<Nmax). Nmax may be user-defined. The plurality N LUTs are generated and saved by applying methods that employ the histogram (e.g., histogram equalization, standard deviation, min-max stretching, linear contrast curves, gamma-based contrast curves, S-shaped contrast curves, Gaussian curves, etc.). The time t[N]s at which each of LUTs L[N]s were generated may be saved.
In one embodiment, the statistical data may also include, optionally, (d) a plurality of M custom LUTs L[M]s, where M is selected between zero and Mmax (i.e., 0<M<Mmax). Mmax may be user defined. The time t[M]s at which the LUTs were generated may be saved. A custom LUT is a LUT generated manually or derived empirically with manual intervention and control.
Hence, in one embodiment, an entry Es is associated with each quad Qs that covers a region Rs having homogenous features Fs. Therefore, there are several entries Es per NUI image as well as for each of its R-sets. A histogram Hs is computed for all pixels within a quad Qs and stored at time ts. Optionally, a plurality of N-computed LUTs L[N]s and a plurality of M-custom LUTs L[M]s may be computed and stored at, respectively, time t[N]s and time t[M]s. Therefore, Es is an object whose members are Qs, Hs, ts, and optionally L[N]s and t[N]s, L[M]s and t[M]s. Given a subjectively homogenous visual feature Fs that covers a geographic region Rs, the corresponding entry Es contains data that is sufficient to quantitatively define the geographic bounds of region Rs and convert all pixels that are within region Rs from a known bit-depth higher than 8-bits per band to 8-bits per band for visualizing these pixels on a 24-bit RGB display device. In one embodiment, Es may be represented as Es(Qs, Hs, ts, L[N]s at t[N]s, L[M]s at t[M]s).
In one embodiment, if the number of regions for a given image is relatively large, optionally, a bounding quad Qb is generated for a group of T quads Qs[T] (where T≧0) based on geographical proximity. In one embodiment, under a single bounding Qb, multiple quads Qs may overlap. In addition, in one embodiment, multiple bounding quads Qb may also overlap. FIG. 5 represents a hierarchical tree or relationship structure between the various quads, according to en embodiment of the present invention. The root of the tree or structure represents the entire image. As shown in FIG. 5, an image is divided into four regions R1, R2, R3 and R4, each defined by quads Qs1, Qs2, Qs3 and Qs4. The quads being defined, the image is further divided into two further quads Qb1 and Qb2. As shown in FIG. 5, Qb1 covers Qs4 completely and Qs1 and Qs3 partially. Also as shown in FIG. 5, Qb2 covers Qs4 completely and Qs1 and Qs3 partially.
In one embodiment, a hierarchical tree of overlapping bounding quads Qb can be generated such that for a given bounding quad Qb:
(a) the siblings of the bounding quad Qb are in the general proximity of the bounding quad Qb;
(b) the bounding quad Qb wholly or partially envelopes the children Qs of the bounding quad Qb; and
(c) the parent of the bounding quad Qb wholly envelopes the bounding quad Qb.
In one embodiment, the root Qb(root) of the hierarchical tree of overlapping plurality of bounding quads Qb is defined as the bounding box of the NUI file, and the leaf nodes at the bottom of the hierarchical tree of overlapping plurality of bounding quads Qb are all entries Es, each entry Es being associated with a corresponding quad Qs.
For example, a single root Qb(root) having a plurality of entries Es (associated with quads Qs) as children can be used. When a search is performed to find a quad Qs containing a pixel Pi (see, FIG. 5), any well known tree-based search algorithm may be used. Consider the tree structure depicted in FIG. 5. If a pixel is in the region defined by Qs2, for example, the search would look for the pixel from the root node Qb(root). From the root node Qb(root), the search would move to node Qb1 because the pixel is within the bounds of Qb1. Within bounding quad Qb1, the sections quads Qs1, Qs2 and Qs3 are stored sorted in ascending or descending order of their geographical coordinates. By applying a known search algorithm through these regions, the pixel that is indeed within the quad Qs2 can be found or located. Once this is known, the selected LUT from the corresponding entry Es2 (associated with the quad Qs2) is applied to convert Pi to the corresponding pixel in the lower bit-depth output image.
FIG. 6 depicts a structure for storing statistical data for the original image and each R-set, each divided into several regions, according to an embodiment of the present invention. This method of generating and storing feature-based statistics for a given image is applied to the original image and all its R-sets within the NUI file. The original image and each of its R-set is divided into several regions, each region Rs for the image or R-set containing an entry Es. The original image and each R-set also store the hierarchical tree to further assist in matching a pixel to a corresponding region quad Qs and hence to the entry Es containing Qs.
FIG. 7 is a flow chart depicting a method of pre-computing the statistical data used for converting a first image of higher bit depth to a second image of lower bit depth, according to an embodiment of the present invention. A NUI file containing an original image and a plurality of R-sets covering a large geographical area containing a variety of visual features, the visual features covering a wide gamut of color-space, are input, at S10. A first method or procedure (method A) is applied to the inputted NUI file, at S20. The method A includes dividing the image (original image) into visually homogenous regions, as described in the above paragraphs, at S22. Pixels within the homogenous regions may overlap. Pixels included in all regions cover or form the entire image. The method A further includes applying a sub-procedure or method B to each region Rs, at S24. The sub-procedure (method B) will be described in detail in the following paragraphs. The method or procedure A further includes determining whether the number of regions within the image is a large number, and if the number of regions within the image is a large number, optionally computing a hierarchical tree to organize all regions into a tree-based structure, at S26. The method A further includes, storing the hierarchical tree-based structure into the file containing the image data, at S28.
The sub-procedure method B includes storing bounds of a region in a quad Qs, at S241. The sub-procedure B further includes computing histogram Hs of all bands for all pixels contained within the quad Qs, and record a time ts at which it was computed, at S242. The sub-procedure method B further includes, optionally computing a number N of look-up tables or LUTs (L[N]s), each LUT containing a pre-computed pixel conversion table for all bands, to convert pixels at a higher-bit depth to a lower-bit depth, and record times at which the LUTs were generated, at S243. The sub-procedure method B may further include, optionally compute an additional number M of look-up tables or LUTs (L[M]s), each containing a user-defined, custom pixel conversion table for all bands, to convert pixels at a higher-bit depth to a lower-bit depth, and record times at which the LUTs were generated, at S244. The sub-procedure method B proceeds by creating an entry Es containing Qs, Hs, and ts, L[N]s and t[N]s, and L[M]s and t[M]s, at S245. The sub-procedure method B further stores the created entry Es into the file containing the image data.
FIG. 8 is a flow chart depicting the method of converting a first image to a second image that can be displayed for a given area of interest (AOI) or viewport in the NUI file, using feature-based statistics and associated data generated earlier, according to an embodiment of the present invention. The method includes, for a NUI file having a pixel depth per band greater than 8-bit per band, selecting a specific LUT from either L[N] or L[M] where N or M is known, at S30. The method further includes, reading pixels from an area of interest (AOI) or viewport from a NUI file, at S32. The areas of interest AOI or viewport can be for example a rectangular area within the bound quad Qb1, as shown in FIG. 5.
A viewport can be defined as a “window” within an image having a pixel width W and a pixel height H. The image can have a large pixel width (e.g., 1,000,000 pixels) and a large pixel height (e.g., 2,000,000 pixels). Such an image cannot be displayed on current display devices (e.g., a screen) in its entirety. In addition, such an image cannot be loaded in computer main memory in its entirety for any form of processing, given current available computer main memory capacity. Hence, an application is forced to load a smaller sub-section, window, area-of-interest or viewport of the very large image. This smaller sub-section, window or viewport has a pixel width VW and pixel height VH which typically range from several tens of pixels to several thousands of pixels (where W>VW and H>VH). For instance, within a 1,000,000 pixel wide and 2,000,000 pixel tall image, a sub-section or viewport starting from pixel coordinate (300000, 450000) within the image and having a pixel width of 1920 pixels and a pixel height of 1080 pixels can be selected. The viewport is wholly contained within the image. Therefore, if (0, 0) is the address of the top left pixel of the W×H image, and if (X, Y) is the address of the top left corner pixel of the VW×VH viewport within the image, then 0≦x≦(X+VW)≦W and 0≦y≦(Y+VH)≦H.
The method further includes for each pixel Pi, traversing Qb(root) to find a Qs that contains Pi, at S34. If the pixel Pi is within multiple overlapping Qs, the Qs having the most recent time ts can be selected. The selected Qs is associated to an entry Es. The entry Es contains the type of LUT that the user selected. The method further includes, for each band in the pixel, determining its 8-bit value and populating the corresponding pixel in the converted image (i.e., converted AOI or viewport), at S36. In one embodiment, the selection of the Qs for each pixel and the determination for each band of the pixel its 8-bit value is performed using parallel processing. However, as it can be appreciated, in another embodiment, this can also be performed using sequential processing. After each pixel is processed as described above, the converted image can then be displayed on a display device (e.g. a display screen), at S38.
The data that is generated using the above outlined procedure can be stored within a NUI file as a NUI Property. In one embodiment, the data can be formatted in Extensible Markup Language (XML) for readability. Alternatively, the data can be stored as a data structure in binary format.
For example, in the case of the continental United States of America (CONUS), if one were to generate multiple NUI image files to cover the entire continental United States, at a resolution of 1 meter per pixel, each NUI can range from few hundred gigabytes (GB) to several terabytes (TB). FIG. 1 depicts the geographical map of the continental United States of America (CONUS). An example of areas covered by the multiple NUI image files are shown as dotted rectangles on the geographical map. On the other hand, if the continental United States is divided into visually homogenous regions or sections (i.e., divided on regions having substantially homogenous features), quadrilateral shaped regions (quad regions) can be defined and shown on the geographical map of the continental United States of America. As shown in FIG. 1, the quadrilaterals can have various shapes including trapezoid shape, rectangular shape, or any other polygonal shape (e.g., pentagonal shape, hexagonal shape, or other more complex shape, etc.). As a result, each of the rectangles defining the NUI images can be divided into several quad regions. For example, as shown in FIG. 1, the NUI image of the area A1 is divided into about 10 homogenous regions or sections R1, R2, . . . , R10.
For each specific homogenous region R1, R2, . . . , R10, a corresponding entry E1, E2, . . . , E10 is available and stored in the NUI file. Any given pixel Pi(x, y) in a NUI file may fall within multiple regions and thus may be associated with a plurality of entries Es. For example, as shown in FIG. 1, a pixel may fall within homogenous section R1 and within homogenous section R3. In other words, the homogenous sections R1 and R3 overlap. As a result, the pixel that falls within both R1 and R3 may be associated with both entryE1 and entry E3. In this case, a simple rule may be applied to identify which entry to select (E1 or E3). For example, the entry E3 can be selected if time t3 is greater than time t1.
A plurality of LUTs (N LUTs) can be generated by applying methods that employ a histogram Hs for all pixels within a given quad. The LUTs are generated using various methods including, histogram equalization, standard deviation, min-max stretching, linear contrast curves, gamma-based contrast curves, S-shaped contrast curves, Gaussian, etc. The N LUTs are then saved in the NUI file. For example, a plurality of LUTs can be generated for region R1 by employing histogram H1 within entry E1. The plurality of LUTs generated for region R1 are saved the NUI file that contains the region R1.
A LUT determines the “look” of the image, after it is converted. The user may manually select what kind of LUT best describes the way in which the user wants to display the image prior to performing the conversion.
In the case where some pixels within a NUI file are replaced by other pixels, Es entries for the regions containing the updated pixels also need to be updated accordingly. In another embodiment, the histogram update can be accomplished by re-computing the histograms Hs and the LUTs in the entry Es for the updated pixels.
As stated in the above paragraphs, in one embodiment, the homogenous regions containing substantially homogenous features can be generated or determined manually based on the perception of a user or determined automatically using feature-detection methods or algorithms. In one embodiment, a database of regions that have substantially homogenous geographic features can be generated manually for the whole globe. The database can then be maintained or updated infrequently to take into account, for example, seasonal changes (spring, summer, fall and winter). Indeed, regions that were, for instance, greener during summer can be covered with snow during winter. As a result, regions that were part of one or more “greener quads” may be annexed to one or more “whiter quads.” In one embodiment, thermal and topological contour maps can be used to extend automation of the process of generating quads with homogenous geographic features. Desired regions having substantially homogenous features can be selected from the database and can be used to generate a list of histogram entries for a given NUI file.
FIG. 2A depicts a converted image from an unsigned 16 bits per band. The converted image contains a significant dynamic range of data, as shown on the top left area and on the bottom right area of the image. The image is converted using a conventional standard-deviation applied to the histogram of the entire image file. A LUT is derived and applied to convert the unsigned 16 bits per band image from the higher bit-depth per band (16 bits per band) to a lower bit-depth per band (8 bits per band) to display or view the converted image on a display device, the display device being configured to display an image having a pixel depth of 8 bits per band. This image shows what the output 8-bit depth image would look like without applying the method of converting an image having a higher-bit depth per band into an image having a lower bit depth per band described herein.
FIG. 2B depicts the same image converted from unsigned 16 bits per band to an unsigned 8 bits per band image according to an embodiment of the present invention. The regions have been shown in FIG. 2C. A histogram was computed for each of the regions. For each region, using the histogram, the corresponding unsigned 16 bit to unsigned 8 bit look-up table was generated using a conventional standard deviation method. The look-up table was then applied to the image within the corresponding region to convert from the original unsigned 16-bit image to a displayable unsigned 8-bit image.
The image shown in FIG. 2B looks “patchy” relative to the image shown in FIG. 2A which is relatively smooth and even. However, the “patchiness” of the image in FIG. 2B is due to the fact that the image in FIG. 2B is divided into polygonal regions (e.g. quadrilaterals) having substantially homogenous features so as to improve local detail by adjusting the dynamic range in each of the regions using statistical information computed for only those pixels that fall within those regions.
FIG. 2C depicts the polygonal layout (e.g., quadrilateral layout) used to divide the image in FIG. 2B into a plurality of regions or sections, according to an embodiment of the present invention. A plurality of LUTs are computed using histograms determined for each of the plurality of regions. As a result, the regions that define the “patchy” image display detail that is better than if a single LUT was derived from the histogram of the entire image, as is the case for the image shown in FIG. 2A.
FIG. 3A depicts an image portion obtained when zooming into the top-left corner region of the image shown in FIG. 2A. FIG. 3B depicts an image portion obtained when zooming into the top-left corner region of the image shown in FIG. 2B. The image portion shown in FIG. 3A lacks contrast and detail of the features in this image portion can not be discerned. On the other hand, the image portion shown in FIG. 3B and covering the same area covered by the image shown in FIG. 3A, is crisp and details of features in this image portion can be discerned.
Hence, the method of computing a histogram for each region in a plurality of regions allow for accommodating a greater dynamic range of color when converting pixel data from higher bit depths per band to lower bit depths per band (e.g., 8 bits per band) for display on a standard 24-bit RGB displays. By pre-computing and storing feature-based statistics or statistical data and histograms within images with the higher bit depths per band, conversion of an area or region of interest from a higher bit depth per band into lower bit depth per band can be directly performed (i.e., performed “on-the-fly”). This would eliminate the need to generate additional for-display-only 8 bits per band image conversion. By eliminating the need to generate additional for-display-only 8 bits per band image conversion, the use of storage disk space can be reduced or minimized.
In some embodiments, programs for performing methods in accordance with embodiments of the invention can be embodied as program products in a computer such as a personal computer or server or in a distributed computing environment comprising a plurality of computers. The computer may include, for example, a desktop computer, a laptop computer, a handheld computing device such as a PDA, etc. The computer program products may include a computer readable medium or storage medium or media having instructions stored thereon used to program a computer to perform the methods described above. Examples of suitable storage medium or media include any type of disk including floppy disks, optical disks, DVDs, CD ROMs, magnetic optical disks, RAMs, EPROMs, EEPROMs, magnetic or optical cards, hard disk, flash card (e.g., a USB flash card), PCMCIA memory card, smart card, or other media. Alternatively, a portion or the whole computer program product can be downloaded from a remote computer or server via a network such as the internet, an ATM network, a wide area network (WAN) or a local area network.
Stored on one or more of the computer readable media, the program may include software for controlling both the hardware of a general purpose or specialized computer or processor. The software also enables the computer or processor to interact with a user via output devices such as a graphical user interface, head mounted display (HMD), etc. The software may also include, but is not limited to, device drivers, operating systems and user applications.
Alternatively, instead or in addition to implementing the methods described above as computer program products) (e.g., as software products) embodied in a computer, the method described above can be implemented as hardware in which for example an application specific integrated circuit (ASIC) can be designed to implement the method or methods of the present invention.
Although the various steps of the method(s) are described in the above paragraphs as occurring in a certain order, the present application is not bound by the order in which the various steps occur. In fact, in alternative embodiments, the various steps can be executed in an order different from the order described above.
Although the invention has been described in detail for the purpose of illustration based on what is currently considered to be the most practical and preferred embodiments, it is to be understood that such detail is solely for that purpose and that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover modifications and equivalent arrangements that are within the spirit and scope of the appended claims. For example, it is to be understood that the present invention contemplates that, to the extent possible, one or more features of any embodiment can be combined with one or more features of any other embodiment.
Furthermore, since numerous modifications and changes will readily occur to those of skill in the art, it is not desired to limit the invention to the exact construction and operation described herein. Accordingly, all suitable modifications and equivalents should be considered as falling within the spirit and scope of the invention.

## Claims

1. A method for determining statistical data for pixels of an image, the pixels having a higher bit depth per band, wherein the higher bit depth per band comprises greater than 8 bits per band, the method comprising:
dividing the image having pixels with the higher bit depth per band into a plurality of polygonal sections, each polygonal section including substantially homogenous features;
computing statistical data for pixels within each polygonal section; and
storing the statistical data with the image;
wherein said computing statistical data for the pixels within each polygonal section comprises:
computing a first plurality of look up tables, each look up table in the first plurality of look up tables comprising a pre-computed pixel conversion table for all bands of each pixel, and times at which the first plurality of look up tables are generated.

2. The method according to claim 1, wherein the substantially homogenous features are determined based on a perception of a user.

3. The method according to claim 1, wherein the substantially homogenous features are determined by a computer algorithm.

4. The method according to claim 1, wherein the plurality of polygonal sections comprise one or more of triangular sections, quadrilateral sections, pentagonal sections, or hexagonal sections, or any combination of two or more thereof.

5. The method according to claim 1, wherein computing statistical data for pixels within each polygonal section comprises computing histograms for the pixels.

6. The method according to claim 5, wherein computing histograms for the pixels comprises computing, minimum value, maximum value, standard deviation, mean, median, mode, skew, or kurtosis, or any combination of two or more thereof, of each band of each pixel in the image.

7. The method according to claim 1, further comprising:
computing a second plurality of look up tables, each look up table in the second plurality of look up tables comprising a custom pixel conversion table for all bands of each pixel, and times at which the second plurality of look up tables are generated.

8. The method according to claim 7, wherein
computing the second plurality of look up tables comprises generating the second look up tables using custom pixel conversion tables defined by a user.

9. The method according to claim 1, further comprising reading pixel data of the image having the higher-bit depth per band, wherein the pixel data of the image is stored in a new universal image (NUI) file.

10. The method according to claim 9, wherein the statistical data is stored with the image in the NUI file.

11. A computer program product comprising a computer readable medium having instructions stored thereon when executed by a computer system performs the method recited in claim 1.

12. A method for determining statistical data for pixels of an image, the pixels having a higher bit depth per band, wherein the higher bit depth per band comprises greater than 8 bits per band, the method comprising:
dividing the image having pixels with the higher bit depth per band into a plurality of polygonal substantially homogenous features;
computing statistical data for pixels within each polygonal section; and
storing the statistical data with the image;
selecting a first image within the image having pixels with the higher bit depth per band, the first image corresponding to a viewport from the image having pixels with the higher bit depth per band;
determining, for each pixel with the higher bit depth per band within the first image, to which polygonal section in the plurality of polygonal sections each pixel belongs to;
converting each pixel with the higher bit depth per band within the first image into a corresponding pixel of a lower bit depth per band using statistical data of a polygonal section to which the pixel with the higher bit depth per band belongs to, wherein the lower bit depth per band comprises 8 or less bits per band; and
forming a second image having pixels of the lower bit depth per band.

13. The method according to claim 12, further comprising:
displaying the second image having pixels of the lower bit depth per band on a display device.

14. The method according to claim 12, wherein computing statistical data for the pixels comprises computing a plurality of look up tables, each look up table in the plurality of look up tables being associated with a corresponding polygonal section of the plurality of polygonal sections.

15. The method according to claim 14, further comprising selecting a specific look up table within the plurality of lookup tables that is associated with the polygonal section to which the pixel with the higher bit depth per band belongs to.

16. A system for determining statistical data for pixels of an image, the pixels having a higher-bit depth per band, wherein the higher bit depth per band comprises greater than 8 bits per band, the system comprising:
a processor configured to:
divide the image having pixels with the higher bit depth per band into a plurality of polygonal sections, each polygonal section including substantially homogenous features;
compute statistical data for pixels within each polygonal section; and
store the statistical data with the image;
select a first image within the image having pixels with the higher bit depth per band, the first image corresponding to a viewport from the image having pixels with the higher bit depth per band;
determine, for each pixel of the higher bit depth per band within the first image, to which polygonal section in the plurality of polygonal sections each pixel belongs to;
convert each pixel with the higher bit depth per band within the first image into a corresponding pixel with a lower bit depth per band using the statistical data of a polygonal section to which the pixel with the higher bit depth per band belongs to, wherein the lower bit depth per band comprises 8 or less bits per band; and
form a second image having pixels of the lower bit depth per band.

17. The system according to claim 16, wherein the processor is configured to compute histograms for the pixels.

18. The system according to claim 16, wherein the processor is configured to compute minimum value, maximum value, standard deviation, mean, median, mode, skew, or kurtosis, or any combination of two or more thereof, of each band of each pixel in the image.

19. The system according to claim 16, wherein the processor is configured to compute look up tables for the pixels using the histograms.

20. The system according to claim 16, further comprising a storage device in communication with the processor, the storage device configured to store pixel data of the image in a new universal image (NUI) file.

21. The method according to claim 20, wherein the statistical data is stored with the image in the NUI file.

22. The system according to claim 16, further comprising:
a display device in communication with the processor, the display device configured to display the second image having the lower bit depth per band.

23. The system according to claim 16, wherein the processor is further configured to compute a plurality of look up tables, each look up table in the plurality of look up tables being associated with a corresponding polygonal section of the plurality of polygonal sections.

24. The system according to claim 23, wherein the processor is configured to select a specific look up table within the plurality of lookup tables that is associated with the polygonal section to which the pixel with the higher bit depth per band belongs to.

25. A method of converting a first image within an image having pixels with a relatively higher bit depth per band into a second image having pixels with a relatively lower bit depth per band, comprising:
selecting a first image, the first image corresponding to a viewport from an image having pixels with the higher bit depth per band, the image having pixels with the higher bit depth per band being divided into a plurality polygonal sections, each polygonal section including substantially homogenous features;
determining, for each pixel with the higher bit depth per band within the first image, to which polygonal section in the plurality of polygonal sections each pixel belongs to;
converting each pixel with the higher bit depth per band within the first image into a corresponding pixel of a lower bit depth per band using statistical data of a polygonal section to which each pixel belongs to; and
forming the second image having pixels of the lower bit depth per band.

26. The method according to claim 25, further comprising:
displaying the second image having pixels of the lower bit depth per band on a display device.

27. The method according to claim 25, wherein the second image having the lower bit depth per band includes an image having a bit depth per band less than or equal to 8 bits per band.

28. A computer program product comprising a computer readable medium having instructions stored thereon when executed by a computer system performs the method recited in claim 25.

29. A system of converting a first image having a relatively higher bit depth per band into a second image having a relatively lower bit depth per band, comprising:
a processor configured to:
select a first image, the first image corresponding to a viewport from an image having pixels with the higher bit depth per band, the image having pixels with the higher bit depth per band being divided into a plurality polygonal sections, each polygonal section including substantially homogenous features;
determine, for each pixel with the higher bit depth per band within the first image, to which polygonal section in the plurality of polygonal sections each pixel belongs to;
convert each pixel with the higher bit depth per band within the first image into a corresponding pixel of a lower bit depth per band using statistical data of a polygonal section to which each pixel belongs to; and
form the second image having pixels of the lower bit depth per band.

30. The system according to claim 29, further comprising:
a display device in communication with the processor, the display device configured to display the second image having the lower bit depth per band.

31. The system according to claim 29, wherein the second image having the lower hit depth per band includes an image having a bit depth per band less than or equal to 8 bits per band.