image upsampling via imposed edge statistics raanan fattal. acm siggraph 2007 presenter: 이성호
TRANSCRIPT
Previous workClassical approach
Nearest-Neighbor, Bilinear, Bicubic, Hann, Hamming, and Lanczos interpola-tion kernels. assumption that
the image data is either spatially smooth or band-limited
More sophisticated methods
[Su and Willis 2004] Reduce the number of variables that are averaged forms a noticeable block-like effect
Bicubic Su and Willis 2004
[Li and Orchard 2001]
Arbitrary edge orientation is implicitly matched By estimating local intensity covariance
from the low-resolution image Generating smooth curves and of reduc-
ing jaggies Not sharp edges
[Freeman et al. 2002]
adding high-frequency patches from a non-parametric set of examples
relating low and high resolutions Sharpens edges and yields images with
a detailed appearance tends to introduce some irregularities
into the constructed image
Assumptions on image upsampling
different upsampling techniques corre-spond to different assumptions: images are smooth enough to be ade-
quately approximated by polynomials yields analytic polynomial-interpolation formulas
images are limited in band yields a different family of low-pass filters
these assumptions are highly inaccurate suffer from excessive blurriness and the
other visual artifacts
Edge-Frame Continuity Moduli
predict the spatial intensity differences at the high-resolution based on the low-
resolution input image
Approach
Statistics of intensity differences intensity conservation constraint we discuss only gray scale images
later extend to handle color images
Color images
First we upsample the luminance channel of the YUV color space
compute the absolute value of its luminance difference
d1 d2
d3 d4
objective error measurements between an upsampled image and theoriginal ground-truth image (i.e., before downsampling).Structural Similarity Image Quality (SSIQ) described in [Wang et al. 2004]
Implementations
implemented in C++ Mobile Pentium-M, running at 2.1MHz Upsample an image of 1282 pixels
to twice its resolution (2562). 2 seconds
To a resolution of 10242 pixels 22 seconds.
Conclusions
Drawbacks: Emphasize lack of texture and absence of fine-details The jaggies artifact Acutely twisted edges involves more computations
than some of the existing techniques generic behavior of edges does not accurately de-
scribe every particular case. Further improve
Using higher-order edge properties Such as curvature