Explore a Variety of Digital Images with MVHimage Software
Purpose: A picture may be worth a thousand words, but convert it into millions of data points. MVHimage is designed to work on any digital image that is found on the Internet (jpeg, gif, tiff, png, pict, and pdf) and pictures from your digital camera.
NOTE: The images that follow are not interactive. Please download the software (OSX OS9 PC) and follow along with the mini tutorial.
Getting Started
First, click on the button labeled 'Select Image'.
After the image is selected, a window will pop up that asks you whether you can calibrate the size of pixels within the image. There are 3 options:
1) Click the button 'Known Pixel Size' if you know the size of the pixels, such as orthophotographs from aerial reconnaissance.
2)
Click the button 'Scale Present in Image' if there is a linear scale located in the image (see example above). This includes images taken with a camera in which a ruler, penny, or other object of known size is located next to the object you are interested in and the camera lens is parallel to the object of interest (not at a slant). Also, graphics of data with a distance scale, such as maps of ozone concentration over the United States that can be downloaded from the Internet, can use this calibration method.
3)
Click the button 'None' if there is no way to calibrate the scale of the pixels to the physical size represented in the image.
If you make a mistake during calibration, click on the button labeled 'Calibrate Scale Tools' to repeat the process.
Scale Present in Image
A window will pop up in which you may draw a line along the scale within the image by moving the cursor onto the image.
Click on the beginning of the scale, which may be a ruler, a penny, or any object of known length.
Hold the mouse button and drag the cursor to the end of the scale.
Release the mouse button.
A line is drawn on the image marking where you clicked on the image and where you released the mouse button.
If the line does not match up exactly, either redraw the line or fine tune the start and stop positions of the line with the small arrows next to the x and y positions of the line end points, which are located below the image.
When satisfied with the fit of the line to the scale, enter the length of the scale in the white box below.
Enter only the number, not the unit of the scale (such as inches or centimeters).
Click the 'Done' button when finished.
Exploring Digital Images
Analysis Tools: There are three tools to analyze colors, lengths, and areas of features in the image.
1) The point tool examines the intensities of red, green, and blue measurements at a pixel within the image.
2) The line tool displays the color intensities for each pixel along a line as well as the length of the line (in pixels and a scale distance, provided calibrated).
3) The area tool calculates the frequency of occurrence of color intensities of pixels within the selected rectangle. The number of pixels within the rectangle are converted to a scaled area, if calibrated.
To use each tool, click the cursor at some point within the image, and drag the cursor to obtain the desired point, line, or rectangular area.
Information of the pixel(s) at the point, along the line, or within the area will be automatically calculated and graphically displayed.
Values of color intensity are scaled from 0 to 100%.
To move the cross hair, line, or area drawn on the image, use the small up and down arrows that are along the right edge of the satellite image. Use these arrows to create a point, line, or area as well.
Use the 'Save Measurement' in the File Menu to add data to a tab-delimited text file, which may be used in any spreadsheet software, such as Excel.
Data in gray window are saved automatically (including labels). Data depends on Analysis Tool selected.
White text boxes available to type additional data to be saved.
Data are added to the end of the file opened for first measurement saved, even if new pictures are analyzed in one session. To add data to an old file, open this file when saving new measurement.
Histograms: A histogram is graph of the number of times values fall within specific ranges. In this case, increments of 5% defined the bins to sort the intensities.
Similar to that generated by the Area Tool, except that the graph is based on all of the pixels within the digital image rather than a selected area.
Average (+/- one standard deviation) of the color intensities appear along the right edge of the graph.
Control the displayed data by using the 'on'/'off' buttons located at the bottom of the floating window.
Display Tools: There are 8 visual enhancements to view the digital image.
1) Red-Green-Blue Colors = standard color presentation of digital imagery in which the color intensities of red, green, and blue are displayed in the computer display's red, green, and blue, respectively.
2-4) Red, Green, or Blue (in Shades of Gray). A gray shade image of only one of the image’s primary colors.
For example, a gray shade image of red displays the pixel's red value in all three colors of the computer's display.
Gray shade images allow viewing of intensities without biasing your sensitivity to red, green, or blue.
For example, if a pixel’s RGB values are 20%, 80%, and 30%, respectively, it will be displayed as 20%, 20%, 20% if the Red (gray) display is selected.
5-7) Red vs Green, Red vs Blue, or Green vs Blue (normalized): For each pixel, display the normalized difference between two color intensities.
(Intensity A - Intensity B) / (Intensity A + Intensity B)
Minimizes the effects of shadows and indirect lighting within the image.
The color of the greater intensity value is displayed.
The larger the normalized difference, the brighter the color.
Colors closer to black represent small normalized differences.
Example: Using 'Red vs Green (normalized)', a pixel with RGB values of 40%, 80%, and 60%, respectively, the difference between red and green is 40% in the green, and the sum of the red and green intensities is 120%.
The normalized difference will be 40% / 120% or 0.33, which is converted to 33% for display purposes.
The displayed color for that pixel will have RGB values of 0%, 33%, 0% (dark green).
Compare this value to another pixel that has RGB values of 0%, 40%, 20%. The normalized difference is 40% / (0% + 40%) which equals 1. This value is converted back to a percentage of 100%. The pixel will be displayed with an RGB value of 0%, 100%, 0% (bright green).
8) Set Range of Colors to Show: Set thresholds to enhance image and use results with Line and Area Analysis Tools.
Display only those pixels that meet thresholds you select.
Pixels meeting criteria are displayed as black, and white pixels represent those that did not meet the criteria.
Number of pixels meeting threshold are displayed.
If pixel size is calibrated, area of highlighted pixels is calculated.
To see the RGB digital image while using another visualization scheme, click on ‘Show Original Image’ and a window with the RGB image will appear.
Drag this image to any position on the computer screen, and use the point, line, and area on this image as well as the enhanced image.
Page Setup and Print: To print the images and graphs, first use 'Page Setup' in the File Menu. Select 'landscape' printing and experiment with the scale for a full-page print. We have found that a scale of 75% works on our printers.
Images may be saved.
Getting Help: Check the 'Help" menu for information on software features when using the software.
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