An OperationDescriptor describing the "Mosaic" operation
in the rendered mode.
The "Mosaic" operation creates a mosaic of two or more source images.
This operation could be used for example to assemble a set of
overlapping geospatially rectified images into a contiguous
image. It could also be used to create a montage of photographs such
as a panorama.
All source images are assumed to have been geometrically mapped into
a common coordinate space. The origin (minX, minY) of
each image is therefore taken to represent the location of the respective
image in the common coordinate system of the source images. This
coordinate space will also be that of the destination image.
All source images must have the same data type and sample size for all
bands. The destination will have the same data type, sample size, and
number of bands and color components as the sources.
The destination layout may be specified by an
ImageLayout hint
provided via a
RenderingHints supplied to the operation. If this
hint contains a setting for the image bounds (origin and dimensions), it
will be used even if it does not intersect the union of the bounds of
the sources; otherwise the image bounds will be set to the union of all
source image bounds. If the data type or sample size specified by the layout
hint do not match those of the sources, then this portion of the hint will be
ignored.
It is permissible that the number of source images be initially zero. In
this case a non-null ImageLayout must be
supplied with valid width and height and a non-null
SampleModel. The destination data type, sample size, number
of bands, and image bounds will all be determined by the
ImageLayout.
If sourceAlpha is non-null, then any non-
null elements of the array must be single-band images
with the same data type and sample size as the sources.
The source threshold array parameter has maximum dimensions as
double[NUM_SOURCES][NUM_BANDS]. Default values of the
thresholds actually used are defined as follows:
- The default value of
sourceThreshold[0][0] is
1.0.
- If
sourceThreshold[i] != null and
sourceThreshold[i].length < NUM_BANDS, then set
sourceThreshold[i][j] = sourceThreshold[i][0] for all
1 <= j < NUM_BANDS.
- If
sourceThreshold[i] == null then set
sourceThreshold[i] = sourceThreshold[0].
The background value array parameter has maximum dimensions as
double[NUM_BANDS]. Default values of the
background actually used are defined as follows:
- The default value of
backgroundValues[0] is
0.0.
- If
backgroundValues.length < NUM_BANDS, then set
backgroundValues[j] = backgroundValues[0] for all
1 <= j < NUM_BANDS.
The default behavior therefore is to set the background to zero.
If a given destination position (x, y) is within the bounds
of M source images, then the destination pixel value
D(x, y) is computed using an algorithm selected on the
basis of the mosaicType parameter value. If the destination
position is not within any source image, then the destination pixel value
is set to the specified background value.
If the mosaicType parameter value is
MOSAIC_TYPE_BLEND, then the destination pixel value
is computed as:
double[][][] s; // source pixel values
double[][][] w; // derived source weight values
double[][] d; // destination pixel values
double weightSum = 0.0;
for(int i = 0; i < M; i++) {
weightSum += w[i][x][y];
}
if(weightSum != 0.0) {
double sourceSum = 0.0;
for(int i = 0; i < M; i++) {
sourceSum += s[i][x][y]*w[i][x][y];
}
d[x][y] = sourceSum / weightSum;
} else {
d[x][y] = background;
}
where the index i is over the sources which contain
(x, y). The destination pixel value is therefore a
blend of the source pixel values at the same position.
If the mosaicType parameter value is
MOSAIC_TYPE_OVERLAY, then the destination pixel value
is computed as:
d[x][y] = background;
for(int i = 0; i < M; i++) {
if(w[i][x][y] != 0.0) {
d[x][y] = s[i][x][y];
break;
}
}
The destination pixel value is therefore the value of the first source
pixel at the same position for which the derived weight value at the same
position is non-zero.
The derived weight values for the ith source are determined from
the corresponding sourceAlpha, sourceROI, and
sourceThreshold parameters as follows where for
illustration purposes it is assumed that any alpha values range over
[0.0, 1.0] with 1.0 being opaque:
// Set flag indicating whether to interpret alpha values as bilevel.
boolean isAlphaBitmask =
!(mosaicType.equals(MOSAIC_TYPE_BLEND) &&
sourceAlpha != null &&
!(sourceAlpha.length < NUM_SOURCES));
if(!isAlphaBitmask) {
for(int i = 0; i < NUM_SOURCES; i++) {
if(sourceAlpha[i] == null) {
isAlphaBitmask = true;
break;
}
}
}
// Derive source weights from the supplied parameters.
w[i][x][y] = 0.0;
if(sourceAlpha != null && sourceAlpha[i] != null) {
w[i][x][y] = sourceAlpha[i][x][y];
if(isAlphaBitmask && w[i][x][y] > 0.0) {
w[i][x][y] = 1.0;
}
} else if(sourceROI != null && sourceROI[i] != null &&
sourceROI[i].contains(x,y)) {
w[i][x][y] = 1.0;
} else if(s[i][x][y] >= sourceThreshold[i]) { // s[i][x][y] = source value
w[i][x][y] = 1.0;
}
As illustrated above, the interpretation of the alpha values will vary
depending on the values of the parameters supplied to the operation. If
and only if mosaicType equals MOSAIC_TYPE_BLEND
and an alpha mask is available for each source will the alpha values be
treated as arbitrary values as for
Transparency.TRANSLUCENT . In
all other cases the alpha values will be treated as bilevel values
as for
Transparency.BITMASK .
It should be remarked that the MOSAIC_TYPE_BLEND algorithm
applied when the weights are treated as bilevel values is equivalent to
averaging all non-transparent source pixels at a given position. This
in effect intrinsically provides a third category of mosaicking. The
available categories are summarized in the following table.
Mosaic Categories
| Mosaic Type |
Transparency Type |
Category |
|---|
MOSAIC_TYPE_BLEND |
BITMASK |
Average |
MOSAIC_TYPE_BLEND |
TRANSLUCENT |
Alpha Blend |
MOSAIC_TYPE_OVERLAY |
BITMASK || TRANSLUCENT |
Superposition |
Resource List
| Name | Value |
|---|
| GlobalName | Mosaic |
| LocalName | Mosaic |
| Vendor | com.sun.media.jai |
| Description | Creates a mosaic of two or more rendered images. |
| DocURL | http://java.sun.com/products/java-media/jai/forDevelopers/jai-apidocs/javax/media/jai/operator/MosaicDescriptor.html |
| Version | 1.0 |
| arg0Desc | Mosaicking type. |
| arg1Desc | Source alpha masks. |
| arg2Desc | Source region of interest masks. |
| arg3Desc | Source threshold values. |
| arg4Desc | Destination background value. |
Parameter List
| Name | Class Type |
Default Value |
|---|
| mosaicType | javax.media.jai.operator.MosaicType |
MOSAIC_TYPE_OVERLAY |
| sourceAlpha | javax.media.jai.PlanarImage[] |
null |
| sourceROI | javax.media.jai.ROI[] |
null |
| sourceThreshold | double[][] |
double[][] {{1.0}} |
| backgroundValues | double[] |
double[] {0.0} |
since:
JAI 1.1.2 | 