Lab 2 Flashcards
What are the three levels of processing involved with perceiving the gist of the scene?
a. low-level features (e.g., color, spatial frequencies)
b. intermediate image properties (e.g., surface, volume)
c. high-level information (e.g., objects, activation of semantic knowledge).
What characteristics must targets in remote sensing images have?
Targets may be a point, line, or area feature. This means that they can have any form, from a bus in a parking lot or plane on a runway, to a bridge or roadway, to a large expanse of water or a field.
The target must be distinguishable; it must contrast with other features around it in the image.
What are the visual elements of image interpretation?
tone, shape, size, pattern, texture, shadow, and association
Describe and differentiate the four categories of image processing functions.
Preprocessing
i. Preprocessing functions involve those operations that are normally required prior to the main data analysis and extraction of information, and are generally grouped as radiometric or geometric corrections.
b. Image Enhancement
i. The objective of the second group of image processing functions
grouped under the term of image enhancement, is solely to improve the appearance of the imagery to assist in visual interpretation and analysis.
c. Image Transformation
i. Image transformations are operations similar in concept to those for
image enhancement. However, unlike image enhancement operations which are normally applied only to a single channel of data at a time, image transformations usually involve combined processing of data from multiple spectral bands.
d. Image Classification and Analysis
i. Image classification and analysis operations are used to digitally
identify and classify pixels in the data. Classification is usually performed on multi-channel data sets (A) and this process assigns each pixel in an image to a particular class or theme (B) based on statistical characteristics of the pixel brightness values.
What is an image histogram? Be specific relative to the x and y axes.
A histogram is a graphical representation of the brightness values that comprise an image. The brightness values (i.e. 0-255) are displayed along the x-axis of the graph. The frequency of occurrence of each of these values in the image is shown on the y-axis.
Why does spectral ratioing diminish topographic effects?
Another benefit of spectral ratioing is that, because we are looking at relative values (i.e. ratios) instead of absolute brightness values, variations in scene
illumination as a result of topographic effects are reduced. Thus, although the absolute reflectances for forest covered slopes may vary depending on their orientation relative to the sun’s illumination, the ratio of their reflectances between the two bands should always be similar.
Which panel of the Image Analysis window would allow you to measure dimensions (e.g., distance) from an image?
The Mensuration panel contains tools to measure point, distance, angle, height,
perimeter, and area from an image (raster dataset or mosaic dataset) with sensor
information (or geodata transformation).
What is the Swipe Layer tool? How does it work?
The Swipe Layer tool is used to interactively reveal layers beneath the layer
being swiped. This tool makes it easy to see what is underneath a particular layer
without having to turn it off in the table of contents. To use the Swipe Layer tool
from the Effects toolbar, choose the layer you want to swipe from the Layer
drop-down menu on the Effects toolbar. Then click and hold as you move the
mouse pointer over the map. You’ll notice that the mouse pointer changes based
on its location. This allows you to choose the direction in which you want to swipe
the layer. By holding down the mouse button and dragging across the display,
the swipe layer is temporarily erased from the view in the direction you are
dragging.
Are outputs from the Image Analysis window temporary or permanent?
The processing is applied to the raster, mosaic dataset, image service, or WCS
layers on the fly. The original data remains unaltered, with the results added as
new temporary layers to the data frame. This is because all the processing tools
output a new temporary raster layer that uses functions to process the data.
Functions allow the processing to be applied quickly and on the fly rather than
creating another data file (which can take time to generate) where the process is
permanently applied. If you want to save the dataset in the temporary layer, you
need to export the raster dataset or you can save the layer file.
What are the two types of kernels that are user-specified? What type of file input is
required for them?
Irregular or weighted kernels, which both use ASCII text files to specify shape or
weights.
What does each band of a multiband raster usually represent?
With multiple bands, each band usually represents a segment of the
electromagnetic spectrum collected by a sensor.
