Perceptual Image Preview

[0001] A preview image typically represents a reduced or downsampled version of a larger image. Imaging applications typically present an image preview on a display device for a viewer to approximate image composition, quality, and/or other aspects of the larger image from which the preview image was derived. However, because preview images are the results of downsampling operations, preview images are created with only a subset of the information present in the corresponding larger images. As a result, a user may not be able to ascertain significant perceptual features that are present in the larger image (e.g., noise, blur, depth of field, white balance, bloom effects, etc.) merely by viewing the preview image. In such scenarios, preview images may not adequately address a user's image previewing and browsing needs.

[0002] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0003] In view of the above, systems and methods for perceptual image preview are described. In one aspect, a naive preview image is generated by downsampling a larger image. Perceptual features of the larger image are then detected. Information associated with the detected perceptual features is then incorporated into the naive preview image to create a perceptual preview image. Since the perceptual preview image incorporates information associated with the detected perceptual features, a viewer of the perceptual preview image will easily detect the presence or absence of such perceptual features in the larger image.

[0004] In the Figures, the left-most digit of a component reference number identifies the particular Figure in which the component first appears.

[0005] FIG. 1 illustrates an exemplary system for perceptual image preview, according to one embodiment.

[0006] FIG. 2(a) illustrates an exemplary arbitrary naive preview image.

[0007] FIG. 2(b) shows an exemplary gradient field inside a region of arbitrary naive preview image of FIG. 2(a).

[0008] FIG. 2(c) shows exemplary arbitrary structurally enhanced perceptual preview image 122 (please see FIG. 1) generated from the arbitrary naive preview image of FIG. 2(a).

[0009] FIG. 2(d) shows an exemplary gradient field inside a region of the arbitrary structurally enhanced perceptual preview image of FIG. 2(c).

[0010] FIGS. 3(a) through 3(e) illustrate various aspects of exemplary noise preservation for synthesized incorporation into a preview image to generate a perceptual preview image, according to one embodiment.

[0011] FIG. 4 shows an exemplary procedure for perceptual image preview, according to one embodiment.

An Exemplary System

[0012] Although not required, the systems and methods for perceptual image preview are described in the general context of computer-executable instructions (program modules) being executed by a computing device such as a personal computer. Program modules generally include routines, programs, objects, components, data structures, etc., that perform particular tasks or implement particular abstract data types while the systems and methods are described in the foregoing context, acts and operations described hereinafter may also be implemented in hardware.

[0013] FIG. 1 shows an exemplary system 100 for perceptual image preview, according to one embodiment. System 100 includes host computing device 102. Host computing device 102 represents any type of computing device such as a small form factor device, a digital camera], a handheld or mobile computing device, a laptop, a personal computer, a server, etc. Host computing device 102 includes one or more processing units 104 coupled to memory 106. Memory 106 includes system memory and any other type of memory coupled to computing device 102 such as compact flash memory, etc. System memory (e.g., RAM and ROM) includes computer-program modules (“progam modules”) 108 and program data 110. Processor(s) 104 fetch and execute computer-program instructions from respective ones of the program modules 108. Program modules 108 include perceptual image preview module 112 for generating a perceptual preview image 114 from a larger (parent) image 116. Program modules 108 also includes “other program modules” 118 such as an operating system, application(s) that leverage aspects of perceptual image preview module 112 (e.g., present perceptual preview images 114 to user, etc.), and/or so on.

[0014] Perceptual image preview module 112 (“preview module 112”) downsamples a larger image 116 to create a conventional naive preview image. Preview module 112 then enhances this naive preview image with additional information associated with the larger image 116 to better show one or more of structure and or perceptual features of the larger image 116. This enhanced naive preview image is a perceptual preview image 114. More particularly, to generate the perceptual preview image 114, preview module 112 detects and evaluates structure and arbitrary perceptual features (e.g., one or more of noise, blur, depth of field, blooming, white balance, and/or so on) from the larger image 116. Such detected structure and arbitrary perceptual features are shown as respective portions of detected perceptual features 120. Preview module 112 enhances the naive preview image with information associated with one or more of these detected aspects to allow a viewer to more accurately ascertain the existence or absence of these aspects in the larger image 116.

[0015] These and other aspects of the systems and methods for perceptual image preview are now discussed in greater detail.

Exemplary Structure Enhancement

[0016] Preview module 112 augments a naive preview image of a larger image 116 with structural enhancements to structurally enhanced preview image 114. These augmentation operations strengthen salient edges and flatten weak details in the resulting image. Since salient edges often separate different objects, this approach typically increases the inter-object contrast and reduces intra-object contrast. As a result, image structure becomes more visually apparent and attractive to a users' attention. The more apparent structure enables a user to more readily detect any information associated with other detected perceptual features 120 that are subsequently incorporated into a structurally enhanced perceptual preview image 114.

[0017] In this implementation, preview module 112 implements structure enhancement via non-linear modulation in the image gradient domain. Because salient edges in spatial domain have large gradient magnitudes, while weak details correspond to small gradient magnitudes, the problem becomes to increase the large gradients and reduce the small gradients. The increase of large gradients strengthens the important edges, and the reduction of small gradients suppresses the redundant details. By solving a Poisson equation, the image can be reconstructed given the gradient field and the image boundary. The adjustment in the gradient field is thus reflected in the resultant image.

[0018] In this implementation, preview module 112 creates a structurally enhanced perceptual preview image 114 by first converting the generated naive preview image to YUV color space. Preview module 112 then computes the gradient field for the luminance component. The chrominance components are kept intact to guarantee that the image color will not change. A modified sigmoid function is used to modulate the gradient magnitudes: $\begin{array}{cc}{G}_i^{\prime }=\frac{\alpha }{1+\exp \left(-k\left(G_i-\beta \right)\right)},& \left(1\right)\end{array}$
where G_i is the gradient magnitude for pixel i and G′_i is the adjusted gradient magnitude. The gradient direction is not changed since local direction adjustment may destroy the consistency of gradient field. Parameter α controls the maximum adjustment magnitude. When α is set to a value smaller than 1, all the gradients will be suppressed. Parameter k controls the modulation slope. The larger k, the more large gradient magnitudes are magnified, and the more small gradient magnitudes are suppressed. Parameter β defines the threshold to differentiate large and small gradient magnitudes. Parameter β has a larger impact on the result than parameters α and k do. To preserve locally salient tiny details, β is chosen adaptively as follows: $\begin{array}{cc}\beta =\{\begin{array}{cc}{\beta }_l,& \mathrm{for}{\beta }_l<{\beta }_g,\\ {\beta }_g,& \mathrm{otherwise},\end{array}& \left(2\right)\end{array}$
where β_g is a global threshold, and β_l is a local threshold. β_l is evaluated as the average gradient magnitudes in the neighborhood of the pixel, weighted by a Gaussian. β_g is evaluated in the same way on the whole image. Equation (2) respects strong edges and favors weak yet salient edges.

[0019] FIG. 2(a) illustrates an exemplary arbitrary naive preview image, according to one embodiment. FIG. 2(b) shows an exemplary gradient field inside the region of the arbitrary naive preview image shown in FIG. 2(a). The region is indicated by box 202 positioned on the tower. FIG. 2(c) shows exemplary arbitrary structurally enhanced perceptual preview image 114 (FIG. 1) generated from the naive preview image of FIG. 2(a), according to one embodiment. FIG. 2(d) shows an exemplary gradient field inside the box 204 of FIG. 2(c), according to the one embodiment. In FIG. 2(d), the gradient directions are kept unchanged as compared to the gradient directions in FIG. 2(b), while the gradient magnitudes are increased for the large gradients and reduced for the small gradients (as compared to the gradient magnitudes of FIG. 2(b)). The structurally enhanced perceptual preview image of FIG. 2(c) presents a clearer image structure as compared to the naive preview image of FIG. 2(a).

Exemplary Perceptual Feature Preservation

[0020] There are many arbitrary types of perceptual features that may be detected from an image 116. Such perceptual features include, for example, white balance, depth of field, blooming, blocky artifacts caused by image compression, image quality, etc. (Blooming is the affect that a dynamic range pixel is overexposed so that the neighboring pixels are brightened and overexposed). To present perceptual features exhibited by a larger image 116 in a perceptual preview image 114, preview module 112 detects such perceptual features (i.e., shown as detected perceptual features 120) from the larger image 116. The number and types of perceptual features represented by detected perceptual features 120 are arbitrary and a function a particular implementation.

[0021] Next, preview module 112 incorporates information (e.g., synthesized/derived information 122) associated with at least a subset of the detected perceptual features 120 into a naive preview image or a structurally enhanced perceptual preview image 114. When the information is incorporated into a naive preview image, a new perceptual preview image 114 results. Although the incorporated information can be information that was extracted from the larger image 116, the incorporated information is not necessarily extracted information. Rather, in some or all instances, such information is synthesized or derived from the information provided by the detected perceptual features 120. In view of this, and in this implementation, exact accuracy of detecting perceptual features 120 exhibited by the apparent image 116 is not necessary. Inclusion of information corresponding to the detected perceptual features 100 into the perceptual preview image 114 allows the perceptual preview image 114 to convey more information to a viewer about the larger parent image 116. For instance, by showing that the detected perceptual features exist to some degree in the parent image 116.

Noise

[0022] Noise is often introduced into an image 116 when the image is captured using a high ISO mode (e.g. ISO 400 or greater), or when a short exposure is used to capture the image. Noise typically appears like color grains that are distributed across the image. Noise usually appears in dark regions. It is assumed that noise has an additive property and complies with uniform distribution. Though this assumption does not always hold if considering various noise generation schemes, it is sufficient for reflecting noise on a structurally enhanced perceptual preview image 114.

[0023] To represent noise present in a larger image 116 in a corresponding perceptual preview image 114, preview module 112 detects and stores the noise from the parent image 116 as source noise image using any of multiple well-known noise detection techniques. Based on the assumption of uniform distribution, preview module 112 generates a destination noise image (with dimensions equivalent to the structurally enhanced preview perceptual preview image 114) by randomly sampling from the source noise image. Such source and destination noise images are shown as respective portions of “other program data” 126 (FIG. 1). The destination noise image is added to the structure enhanced preview image to represent the noise of the larger parent image 116. In another implementation, the destination noise image is added to the naive preview image, rather than the structurally enhanced perceptual preview image 114.

[0024] In one implementation, noise is not detected from a large image 116, but rather only from a uniform smaller region of the larger image 116, for example, from a region that includes few salient edges. The objective is to present noise in the resulting perceptual preview image 114 that looks similar to that one that would be viewed on the larger image 116. It is unnecessary to extract noise from the whole original image 116. For instance, suppose the uniform region Ω is expected to have a size of M×M pixels, where M is of a mild value, say 10d, in which d is the rate of size reduction. Too large M will make the desired uniform region non-existent. Too small M will not provide accurate enough noise.

[0025] In one implementation, instead of detecting Ω in the larger image 116 directly, preview module 112 searches a corresponding region Ω_d of size (M/d)×(M/d) pixels in the naive preview image, then maps it to Ω of the original image 116. The naive preview image will exhibit less noise than present in the larger image from which it was derived. Additionally, because the naïve preview image has a much smaller dimension, the search for Ω_d is efficient and reliable. More specifically, preview module 112 divides the naive preview image into non-overlapped blocks, and selects the block Ω_d that has the smallest variance. In most cases, the region Ω that corresponds to Ω_d contains no salient edges. Therefore, its high frequency components compose the noise map N_s. Preview module 112 applies discrete stationary wavelet transform to reliably estimate noise N_s. Because the region size is quite small, the computation is very fast.

[0026] In one implementation, to produce the noise map N_d with the reduced dimension, preview module 112 utilizes texture synthesis methods to keep the noise spatial distribution in N_s. In practice, preview module 112 randomly generates a noise map N_d from N_s based on the assumption that noise has a uniform distribution. Though N_d does not exactly match the noise distribution in the original image 116, N_d conveys users a similar visual experience as the original one (see FIG. 4, which is described below). To improve algorithm stability, preview module 112 chooses Kuniform regions and randomly samples in all regions. In this implementation, M=80, and K=5. The final image I_f is computed as follows,
I_f=I_d+γ·N_d,
where I_d is the reduced image, and γ is a parameter to control how salient the noise need to be visualized.

[0027] FIG. 3 illustrates exemplary noise preservation for incorporation into a perceptual preview image 114, according to one embodiment. FIG. 3(a) shows an original image 116 from which a perceptual preview image 114 is to be generated, according to one embodiment. FIG. 3(b) shows the visible noise of box 302 of FIG. 3(a) for better visual inspection of the exhibited noise. FIG. 3(c) shows an exemplary detected noise map generated from the noise shown in FIG. 3(b). FIG. 3(d) shows an exemplary naive preview image of the larger image in FIG. 3(a). Please note that FIG. 3(d) does not exhibit any noise is present in the original image of FIG. 3(a). FIG. 3(e) shows a perceptual image preview image 114 that more accurately represents the noise present in the larger image of FIG. 3(a), according to one embodiment.

Blur

[0028] Blur in an image 116 occurs when a relative motion happens between an image acquisition device such as a camera and subject(s) of the image or when the subjects are out of focus. In different situations blur may appear over the whole image or just around some regions. Blur reduces image 116 sharpness. However, a naively reduced image may still look sharp, especially when blur in the corresponding parent image from which the naïve preview image is generated is not serious. Preview module 112 detects image blur for presentation in a perceptual preview image 114. This is accomplished by evaluating blur degree locally in the original image 116. In view of the evaluation, preview module 112 blurs a corresponding region in the perceptual preview image 114 to present a corresponding amount of blur. Edge region blur is generally more visible to a user when the whole image 116 is blurred. In view of this, when the whole image 116 is blurred, preview module 112 performs blur manipulation in the perceptual preview image 114 only along its edges.

[0029] Preview module 112 performs edge detection on a structurally enhanced perceptual preview image 114. For each edge pixel E_i in the image, preview module 112 estimates its respective blur degree. Blur estimation is based on the observation that blurry edge regions usually have a smaller deviation among gradient angles than sharp edge regions do. More specially, for the edge pixel E_i, the region R_i is located in the original image 116 that is shrunk to this pixel E_i. The gradient angles in the region R_i are then denoted as A_i(k). The amount of blurring B_i at edge pixel E_i is computed as follows:
B_i=exp{−η·D(A_i)^α},   (3)
where D(A_i) is the variance of the gradient angles in the region R_i. The parameters η and α control the estimated amount of blur. These are set empirically to η=3, and α=1.2. These parameters can also be determined subjectively.

[0030] Preview module 112 then synthesizes blur in the perceptual preview image 114 in the neighborhood of pixel E_i according to the estimated amount of blur degree associated with the pixel. More particularly, preview module 112 implements blur operations using a Gaussian kernel according to the amount B_i of blur, where B_i is actually as the sigma of the Gaussian. The neighborhood of E_i is then weighted using the Gaussian kernel.

An Exemplary Procedure

[0031] FIG. 4 shows an exemplary procedure 400 for perceptual image preview, according to one embodiment. For purposes of exemplary illustration and description, the operations of the procedure are described with respect to components of FIG. 1. At block 402, perceptual image preview module 112 (FIG. 1) generates a naive preview image from a larger image 116 by downsampling the larger image 116. At block 404, perceptual image preview module 112 detects edge information from the naive preview image. At block 406, perceptual image preview module 112 utilizes the detected edge information to enhance structure of the naive preview image, and thereby creates a perceptual preview image 114 with enhanced structure (a structurally enhanced perceptual preview image). At block 408, perceptual image preview module 112 detects perceptual features (detected perceptual features 120 of FIG. 1) from the larger image 116.

[0032] At block 410, perceptual image preview module 112 incorporates information associated with at least a subset of the detected perceptual features 120 into a preview image to create a perceptual preview image 114. The particular preview image into which such information is incorporated can either be a naive preview image or a structurally enhanced perceptual preview image 114. At block 412, perceptual image preview module 112 or a different application that leverages output of the perceptual image preview module 112, presents the perceptual preview image 114 to a user to represent the larger image 116 from which the perceptual preview image 114 was derived. Since the perceptual preview image 114 presents information associated with detected perceptual features of the larger image 116, viewing the perceptual preview image 114 allows a user to make educated determinations as to the quality or other aspects of the larger image 116.

Conclusion

[0033] Although the systems and methods for perceptual image preview have been described in language specific to structural features and/or methodological operations or actions, it is understood that the implementations defined in the appended claims are not necessarily limited to the specific features or actions described. For example, information associated with detected perceptual features 120 that have been incorporated into a perceptual preview image 114 can be used to allow a user to assess aspects of the larger image in addition to image quality (e.g., depth of field, etc.). Accordingly, the specific features and operations of system 100 are disclosed as exemplary forms of implementing the claimed subject matter.