WILD 5750/6750
LAB 5
10/04/2010
IMAGE MOSAICKING
MOSAICKING:
The MOSAIC
Imagine tool
The Imagine MOSAIC tool
Often, a study area will fall
across two raster data sets
allowing for the need to mosaic
(or merge) data sets together.
The Imagine MOSAIC tool
The Mosaic tool allows us to merge
multiple raster data sets (of the same
type) such as satellite imagery, aerial
photography, or Digital Elevation
Models into one continuous file.
Several issues must be considered when
mosaicking images together:
•Select a “base” image”
•Resampling Method
•Same map projection
•Mosaic Method (overlap function)
•Need for image balancing or color
corrections
The Imagine MOSAIC tool
The Imagine MOSAIC tool
Resampling Method
Resampling Method: As discussed in
class, each resampling method utilizes a
different data sampling algorithm.
Ensure that you select the proper method
for your study.
Using the EDIT  SET OVERLAP
FUNCTION menu, the user can specify
the data overlap function desired.
The Imagine MOSAIC tool
Mosaic Method (overlap function)
•Overlay: The overlap area belongs to the last image opened, which is
on top in the stacking order. Often, for analysis, this is the preferred
overlap method.
•Average: The value of each pixel in the overlap area is replaced by the
average of the values of the corresponding pixels in the overlapping
images.
•Minimum: The value of each pixel in the overlap area is replaced by
the lesser value of the corresponding pixels in the overlapping images.
•Maximum: The value of each pixel in the overlap area is replaced by
the greater value of the corresponding pixels in the overlapping images.
•Feather: The overlap area is replaced by a linear interpolation of the
pixels in the overlap. A pixel in the middle of the overlap area is 50% of
each of the corresponding pixels in the overlapping images. A pixel
1/10 of the overlap from an edge would be 90% one image and 10% the
other.
The Imagine MOSAIC tool
Color Corrections
Using the Histogram Matching:
-extract the histogram of the base image and
use and algorithm to extrapolate it to the
other image(s)
The Imagine MOSAIC tool
Other Details
•Note that images being mosaiced must be in the same
projection.
•Numerous file input types may be used (i.e. jpeg, tiff, dem,
grid, img), however, the output mosaiced image will always
be .img (ERDAS Imagine Format).
•Size and processing time should be considered when
merging to high resolution data sets.
•If images were georeferenced with different accuracies,
there may be feature (i.e. road, stream, agriculture) offsets
across the image cutline.
The Imagine MOSAIC tool
The Process
•From the EDIT  ADD IMAGES menu, select
the images you wish to mosaic.
•Determine the proper overlap function, resample
method, and if color balancing is needed.
•If using the OVERLAP method as your
overlap function, determine what image
should fall on top of the others. This is done
using the SEND SELECTED IMAGES
buttons on the toolbar.
•From the PROCESS  RUN MOSAIC menu,
start the mosaic process. The user will be
prompted for a Output File Name and Location.
The Imagine MOSAIC tool
The Process
Assignment
Use the images supplied in the Lab5 folder, and the instructions
contained in the tutorial “Lab5_Mosaic_TourGuide.pdf ”.
1.
Provide a screen shot of your resulting image (mosaic) for the
exercise that uses air photos. (a) Why did you have to use a cutline?
(b) Why do you think that it is best to use linear landmarks (rivers or
roads) when drawing cutlines?
2. Provide a screen shot of your resulting image (mosaic) for the exercise
that uses Landsat scenes. (a) Why do you think that a color correction
(specifically histogram matching) was applied? Now, other
scenario…assume that you had applied a radiometric correction
(meaning that instead of raw digital numbers now you have
reflectance values) to these images prior to mosaicking… would you
still use the color correction (histogram matching)? Why?
3. Provide a screen shot of your resulting image (mosaic) for the exercise
that uses color infrared photos. Why do you think that a color
correction (color balancing) was applied?
Note:
This lab assignment is due on October 11th, 2010.
Email your work to: doug.ramsey@usu.edu