Streaming Multigrid for Gradient-Domain Operations on Large Images

links description executable usage

LINKS
SIGGRAPH 2008 Paper and Supplemental Images
St James Visualization
Windows Executables
Source Code
License

CODE DESCRIPTION

GradientComposite: Given a set of (aligned) images and a label file prescribing the index of the source image associated to each pixel, this executable outputs the gradient field that is the composite of the gradient fields of the different source images (with partials across the seams set to zero).
GradientsToImage: Given a desired gradient field, this executable solves the Poisson equation to output the image whose gradients are a best-fit to the desired field.

EXECUTABLE ARGUMENTS

GradientComposite:

--in <input image list>
This string is the name of the file containing the (ordered) list of images making up the panorama.
--outX/--outY <output X/Y partials>
These string are the names of the files to which the partial derivatives with respect to x and y will be written out. The suffixes of these files must be the same, and must be one of int/int16/half/float/double. The suffix of the files dictates the format in which the partials are written out to disk.
--labels <label image>
This string is the name of the image encoding the indices associated to each pixel. The index is read off from the red channel of the pixel and values out of range indicate a pixel with no associated image information. (If more than 255 indices are needed, the function LabelIndex can be modified to use all three color values to define the index.)
[--positions <position list>]
This optional string is the name of the file giving the x and y starting offsets for each image. The coordinates should be white-space-delimited integer pairs (in ASCII format) with one pair per image.
[--lScale <label index multiplier>]
This optional integer gives the factor by which the value in the red channel in the labeling image is to be divided in order to obtain the pixel's index. (The default value is 1.)
[--hFill]
If this optional argument is specified, gradients across a seam from label pixels with index in range to pixels with index out of range is set to zero, resulting in a harmonic filling in of regions with unknown gradient values.
[--noPad]
By default, the executable adds a bottom row and left column of zero-valued pixels in order to eliminate artifacts that would otherwise arise when zero-padding the gradients so that the image resolutions are divisible by a sufficiently large power of two. If this optional argument is specified, the additional column and row are not added.
[--progress]
If this optional argument is specified, the executable will output the progess of the gradient composition to stdout.

GradientsToImage:

--inX/--inY <input X/Y partials>
These string are the names of the files from which the partial derivatives with respect to x and y will be read in. The suffixes of these files must be the same, and must be one of int/int16/half/float/double. The suffix of the files dictates the format in which the partials are written out to disk.
If the --noPad flag is not specified, then for a WxH image, the x-partials will be of dimension Wx(H+1) and the y-partials will be of dimension (W+1)xH. Otherwise the dimensions should be (W-1)xH and Wx(H-1) respectively. Each entry should consist of a triplet of values corresponding to the partials of the red, green, and blue channels, and should be written out in binary format.
--out <output image>
This string is the name of the file to which the image solving the Poisson equation will be written out.
--width/--height <image dimensions>
These integer values give the dimensions of the output image.
[--average <average output RGB>]
This optional triplet of floating point values specifies the desired average color of the output image.
[--iters <Gauss-Seidel iterations>]
This optional integer values gives the number of Gauss-Seidel relaxation steps to be applied in the restriction and prolongation phases of the multigrid solver. (By default, this value is equal to 5.)
[--inCoreRes <in-core resolution>]
This optional integer value gives the resolution at which the solver should transition from being in-core to being out-of-core. (By default, this value is equal to 1024.)
[--minMGRes <minimal grid resolution>]
This optional integer value bounds the resolution of the coarsest grid in the multigrid solver. (By default, this value is equal to 64.)
[--temp <scratch directory>]
This optional string specifies the directory to which the temporary I/O streams used for storing data between the restriction and prolongation are to be written out.)
[--quality <output image quality>]
This optional integer value in the range [0,100] specifies the desired quality of the output image. (By default, this value is equal to 100.)
[--noPad]
By default, the executable assumes that a bottom row and left column of zero-valued pixels were added in computing the gradients of the iamge. If this optional argument is specified, the additional column and row are not assumed.
[--verbose]
If this optional argument is specified, the magnitudes of the constraints and the residuals will be written out to stdout for each resolution of the restriction and prolongation phases.
[--fullOOC]
If this optional argument is specified, the data in the I/O streams will be written out as as single-precision floating point values, rather than half-precision values.

USAGE
For testing purposes, several image datasets are provided.

PNC3: This dataset, courtesty of Matt Uyttendaele, consists of a panorama of 7 images resulting in an image of resolution 7,963 x 3,589.
To obtain the gradient field, we execute:
GradientComposite.exe --in images.txt --outX dx.half --outY dy.half --labels labels.png --hFill --positions srcpos.txt
which gives an output of:
Input Size: 7963 x 3589 Average: 81.166594 94.873757 109.569944
Given the desired gradient fields and the computed average color value, the best-fit image is obtained by running:
GradientsToImage.exe --inX dx.half --inY dy.half --out pnc3.jpg --average 81.166594 94.873757 109.569944 --width 7963 --height 3589
The resulting, stiched, image is:
Note that since the --hFill flag was enabled when the gradient field was generated, the reconstruction smoothly extends the image into the unlabeled pixels.
Edinburgh: This dataset, courtesty of Brian Curless, consists of a panorama of 25 images resulting in an image of resolution 16,950 x 2,956.
To obtain the gradient field, we execute:
Input:
GradientComposite.exe --in images.txt --outX dx.half --outY dy.half --labels labels.png
Output:
Input Size: 16950 x 2956 Average: 78.278509 96.306657 114.776703 Input:
GradientsToImage.exe --inX dx.half --inY dy.half --out edinburgh.jpg --average 78.278509 96.306657 114.776703 --width 16950 --height 2956
Output:

Note that since the --hFill flag was not enabled when the gradient field was generated, the reconstructed image preserves the boundary between the labeled and unlabeled pixels.
Redrock: This dataset, courtesty of Aseem Agarwala, consists of a panorama of 9 images resulting in an image of resolution 19,588 x 4,457.
To obtain the gradient field, we execute:
Input:
GradientComposite.exe --in images.txt --outX dx.half --outY dy.half --labels labels.png --lScale 20
Output:
Input Size: 19588 x 4457 Average: 124.306111 117.633504 102.756149 Input:
GradientsToImage.exe --inX dx.half --inY dy.half --out redrock.jpg --average 124.306111 117.633504 102.756149 --width 19588 --height 4457
Output:

Note that since the label files has successive color indices changing by (20,20,20), we added the parameter --lScale 20.

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