Draw a Fixed Circle Imagej

Part 1: Practice Using Pick Techniques³

Sometimes you lot're interested in manipulating or analyzing unabridged images, but it's more common to exist interested in a only part of an epitome. Identifying the pixels you're interested is one of the cardinal tasks in epitome processing, and ImageJ provides a wide range of tools and techniques for making selections.. Another name for a pick is Region Of Interest or ROI. The phrase "select, and then human activity" is a cornerstone of many calculator applications, and paradigm processing is no exception.

In many cases, the instructions won't tell you explicitly what to do, merely nosotros urge you to Try EVERYTHING YOURSELF! Option is such an important procedure that there are no fewer than 15 separate tools on the ImageJ toolbar and over twenty card items dedicated to selections. Your mastery of ImageJ depends largely on your ability to make and use selections.

If you have used other graphic software, you may be frustrated that you tin't draw points, lines, shapes, and text with ImageJ. That's because the process of selecting is of primary importance, and drawing is secondary. It can exist done just information technology takes an extra step, which you'll acquire about afterward.

Prepare a Option Do Image

You'll demand an image to practice these selection techniques on. Nosotros'll apply this paradigm of downtown Pasadena, California for most of our selections.

• Click this paradigm to open up information technology every bit a full-size image. Correct-click (PC) or control-click (Mac) the image to download it to your computer. Then, open the image in ImageJ using any of the techniques you lot've learned. For orientation, North is to the right.

If yous open up the fifty% reduced-resolution version beneath, features will be more than difficult to see and the image scale volition be 1 meter per pixel, non 0.5 meters per pixel (2 pixels/meter).

Colors

In ImageJ, there are 3 colors the user can define:

• Foreground – The foreground color is the default colour for drawing, painting, and filling.
• Background – The background colour is the color used for erasing and deleting.
• Selection – The choice color is the color used to display selection outlines.
The foreground colour, not the selection color is used to draw lines and shapes on the image.

Choose a Selection Colour

Selections are indicated past a colored outline. You take control over the color of the selection outline. If yous have trouble seeing the pick on top of the image (red on red, for case), you might want to change the selection colour to something that is easier to see. The default selection color is yellow, but this can be changed to any of eight standard colors (black, white, red, greenish, blueish, cyan, magenta, xanthous, and orange).

• Choose Edit > Options > Colors and choose a selection color. (The default yellow is skilful—nosotros simply wanted you to see where to alter it if you need to after.

  

  
  

Selection Tools

Accessing Selection Tools and Tool Options

At any given fourth dimension, eight selection tools are visible on the ImageJ toolbar. The tool buttons marked with small red triangles incorporate two or more related tools. To admission the other tools, right-click (PC) or control-click (Mac) the tool button and select from the pop-up tool menu.

Some selection tools take options, such as the width of line selections. There are usually two means to access these settings:

• Double-click the tool button itself. For instance, double-clicking the directly line selection tool opens the line width dialog box. This action is contextual. Double-clicking the Arrow tool opens the Arrow Tool options dialog box.
• Go to the Edit > Options submenu. You'll find the aforementioned options listed.

Select and de-select the unabridged epitome

The two most bones selections are to select everything and select zilch. In a foreign twist of logic, both of these options usually produce the same results. When goose egg is selected in an image, almost operations assume that you want to use the entire image (ALL of the pixels). Operations that require a selection generally display an alarm bulletin to that effect.

• If necessary, zoom out so you can run across the entire image on your monitor. The easy fashion to fit your image to your monitor is to double-click the magnifying drinking glass tool on the ImageJ toolbar. (This is important because if yous can't see the edges of the image you won't see the yellow outline around the image when it's selected.)
• Choose Edit > Selection > Select All. Yous should see a yellow option outline around the outer edge of the epitome.
Yous may know that you can abolish a selection by clicking anywhere outside the option. When the whole image is selected, there is no "outside". The only way to abolish the selection is to de-select the epitome, or to "select none" of the pixels.
• Choose Edit > Selection > Deselect All – The yellow option outline should be gone.
Remember, if you are zoomed in on one part of the image, at that place may be a selection outline somewhere that you tin can't run into. When in doubt, utilise Select None to cancel all selections.

Annotation that many frequently-used carte du jour items have keyboard shortcuts. The keyboard shortcut for Select All is the A cardinal, and the shortcut for Select None is Shift-A.

• Try these shortcuts out. (Notation: Keyboard shortcuts work except when you're entering text using the text tool, for obvious reasons.)
• Before continuing, brand sure nothing is selected.

Line Tools – Straight Line Selection

Straight line selections are used for measuring length (altitude) and angle, and for defining sources for contour plots.

• Use the Directly Line pick tool to make a straight line selection anywhere in the center of the image. As you drag your selection, the ImageJ condition bar shows the length of the line and its angle measured ±180° from the iii o'clock position (0°). Positive angles are measured counterclockwise from 0° to 180° and negative angles are measured clockwise from 0° to -180°.
  
• The small white boxes at the middle and ends of the line selection are handles. Elevate the center handle to move the selection without irresolute its length or angle.
• Drag either end handle to motility that cease of the selection while the other end remains fixed.
• Direct line selections can exist dragged beyond the boundaries of the image window.
  Modifier Keys
  • Shift – Constrains the line pick to horizontal or vertical. (Very useful when setting the scale.)
  • Alt/Selection – When dragging an finish handle, this keeps the line length fixed while changing the angle. (AKA "Radar" mode)
  • Ctrl/Command – Elevate either cease of the line to rotate it about its middle and change its length symmetrically. (AKA "Propeller" mode) When you are zoomed in on an image, this modifier forces the ends of the line to start and stop on whole number pixel coordinate values (attempt information technology to run into what this means).
  • Arrow Keys – The four arrow keys are used to "nudge" selections one pixel at a fourth dimension to the left, correct, upwards, and downwards. (This is the only time nudging volition be mentioned, merely remember that it works for ALL selections. It does not, however, allow you motion any role of a selection exterior the boundaries of the image. When in that location is no active selection, the up and down arrows function as "zoom in" and "zoom out" shortcuts.)
• Test each of these modifiers separately and in combinations. (non all combinations volition work). For example, tin can you lot exercise both "radar" and "propeller" modes at the same time? How about all iii?
• Open the gel sample image (File > Open Samples > Gel).
• Apply the straight line pick tool to select a vertical line down the center of the third lane from the left.
• Choose Analyze > Plot Profile.
• Double-click the straight line choice tool button on the ImageJ toolbar to open the Line Width dialog box, and prepare the line width to xx.
• Activate the gel.gif image window and make another profile plot. Compare the two plots made from dissimilar width line selections.
• Set up the line width dorsum to 1 pixel.
• Close the gel, plot, and Line Width windows.
• Returning to the Pasadena aeriform paradigm, set the scale (spatial calibration) for this image using the directly line selection tool to measure the width of the superhighway overpass (lesser right) at the identify where it crosses the center of the freeway. The width of the overpass is 33 meters. (Tip: Zoom in to the overpass before selecting information technology, and use the shift key to strength the line to be vertical.)
• Check your spatial calibration by measuring the long dimension of the parking structure in the lower left quadrant of the paradigm.
• Do y'all run across the remains of a helipad toward the left end of the parking structure? Standard helipad markings are a circle or foursquare 15 meters across. Exercise these markings see the standard?

Line Tools – Segmented Line Selection

Segmented line selections are used for the same purposes as straight lines. Practise Non, withal, use the segmented line tool to make polygon expanse selections. At that place is a different tool for that purpose.

• Right-click (PC) or control-click (Mac) the line selection tool on the ImageJ toolbar and cull the Segmented Line choice tool from the pop-up tool carte du jour.
• Create a segmented line selection anywhere on the Pasadena image.
Each click defines a new line segment. As you lot are selecting, the ImageJ status bar shows the length and angle of the electric current segment. To end the choice, either double-click the concluding endpoint or click in the pocket-sized box at the start of the line selection. (Don't worry, this won't connect the two ends of the selection.)
• One time selected, the handles at each vertex of the line can be dragged to new locations to refine the selection. If yous accidentally click too far from a vertex and the selection disappears, use the Restore Option command.
• To movement a segmented line selection, move the cursor over the selection until it becomes an arrow, then drag. Segmented line selections tin can be dragged across the boundaries of the image window. As you lot drag, the status bar reports information about the bounding box of the pick (the smallest rectangle to completely contain the option): center (x,y), size (west,h), and aspect ratio (ar). Aspect ratio is only the ratio of the width to the summit of the box. An attribute ratio of ii.5 means that the width is two and a half times the height.
  Modifier Keys
  • Shift – Shift-click a handle to split it into ii split handles to add more detail to the selection.
  • Alt/Option – Alt- or Option-click a handle to delete it.
• Test each of these modifiers earlier continuing to the adjacent tool.

Line Tools – Freehand Line Selection

Freehand line selections are used for the same purposes as straight and segmented lines. Don't use the Freehand Line tool to make freehand expanse selections—at that place is a different tool for that purpose.

• Right-click (PC) or control-click (Mac) the line tool button to select the Freehand Line selection tool.
• To select using this tool, merely click and drag the cursor effectually the image.
• To move a freehand line selection, motion the cursor over the selection until it becomes an pointer, then drag.
• Freehand line selections can be dragged across the boundaries of the image window. Equally you drag, the condition bar reports data near the bounding box of the selection.
• Modifier keys have no effect on freehand line selections.

Line Tools – Arrow Tool

Arrow selections are used for annotating (marking and labeling) images. Yous'll learn how to describe arrows and other shapes later. For at present, just exercise making arrow selections.

• Right-click (PC) or command-click (Mac) the line choice tool on the ImageJ toolbar and choose the Arrow Tool from the pop-up tool carte.
• Double-click the Arrow Tool button to open the Arrow Tool dialog box.

  

  
  
• The Arrow Tool dialog box lets you fix the width (of the line), size (of the head), color, and style (of the caput) of arrows. You can also choose the arrow color and options for outlined and double-headed arrows.

  

  
  

Rectangle Tool

The Rectangle Tool is used to select rectangular areas to measure, analyze, or crop.

• Right-click (PC) or control-click (Mac) the Rectangle selection tool on the ImageJ toolbar and choose the Rectangle tool from the popular-up tool menu.
• Create a rectangular selection anywhere on the Pasadena image. The normal option mode is to drag from 1 corner of the rectangle to the opposite corner, in any direction.
• As yous select or alter rectangles, the status bar reports the coordinates (of the cursor), dimensions, and aspect ratio of the rectangle.
• Once selected, the handles at each corner and side of the rectangle can be dragged to refine the selection. If you accidentally click as well far from a handle and the selection disappears, use the Restore Option command.
• To motility a rectangular selection, move the cursor over the selection until information technology becomes an arrow, then drag. Rectangular line selections can be dragged across the boundaries of the image window.
  Modifier Keys
  • Shift – Constrains the option to a square.
  • Alt/Selection – Afterward selecting, concord down the Alt or Option key to alter the width and height by one pixel at a fourth dimension using the four pointer keys. Only the bottom and right sides of the selection move. Lookout the changing top, width, and aspect ratio in the ImageJ status bar.
  • Command (Mac)/Control (PC) – Draws or resizes rectangle from the center.
  • Shift – Constrains the selection to a foursquare.
  • Command-Option (Mac)/Control-Alt (PC) – Maintains the current aspect ratio as the square is resized.
  • Predict what will happen if you brand a rectangular selection holding downwardly the Command-Shift (Mac) or Command-Shift (PC) keys.
  • Select and measure the surface area of the rectangular block containing the park and apartment buildings.
• Examination each of these modifiers earlier continuing to the side by side tool.

Rounded Rectangle Tool

The Rounded Rectangle Tool pick tool is an annotation tool, used for cartoon on and labeling images. Since it is not strictly a selection tool, information technology appears in the foreground color, not the selection color.

• Correct-click (PC) or control-click (Mac) the Rectangle pick tool on the ImageJ toolbar and choose the Rounded Rectangle Tool from the pop-up tool bill of fare.
• The behavior and modifiers for the Rounded Rectangle Tool are identical to the Rectangle Tool.
• Double-click the Rounded Rectangle Tool in the ImageJ toolbar to open up the tool's options dialog box.

  

  
  
• Exercise making rounded rectangle selections using different corner diameters, stroke (line) widths, colors, and fills earlier continuing to the next tool.

Oval Selections Tool

The Oval Selections Tool and its modifier keys work similar the Rectangle Selection tool to select oval regions.

• The status bar reports the coordinates, dimensions, and aspect ratio of the oval selection'south bounding box.
• Drag the oval selection handles to refine the selection.

Elliptical Selections Tool

The Elliptical Selections Tool and its modifier keys work like the Rectangle Selection tool to select oval regions.

• No information is reported in the status bar for elliptical selections.
• Elevate the elliptical selection handles to refine the option. If you accidentally click as well far from a handle and the selection disappears, use the Restore Choice command.
• Use either the Oval or the Elliptical Choice Tool to measure the area of the circular parking area on the center left edge of the cake containing the park. (Hint: Use the modifier keys to select a circumvolve from the center out.)

Selection Castor Tool

The Selection Brush Tool lets you lot create or arrange a pick using a circular "castor". This tool is especially useful for touching up selections and for making visual selections of regions that don't take distinctive geometric or color characteristics.

• Moving the brush from outside an existing selection into the selection shrinks (subtracts from), moving the castor from inside the pick out expands (adds to) the selection.
• The status bar reports whatsoever changes in the choice bounding box equally you lot brand changes.
• The castor diameter can exist adjusted past double-clicking the Castor Option Tool push on the ImageJ toolbar.

  

  
  Modifier Keys
  
• Shift – Always add the brush to the selection.
• Alt/Option – Always subtract the brush from the selection.

Apply the Selection Castor Tool to measure out the largest grassy area of the park (bounded past sidewalks). Where the trees are in the way, assume there is grass nether them, correct up to the edges of the sidewalks.

Polygon Selection Tool

The Polygon Selection Tool works like the Segmented Line Tool to trace areas by clicking at vertices around the polygon. To complete a selection, either double-click the final point or click in the modest box at the beginning of the get-go side of the polygon.

• Vertices are handles that can exist moved.
• The status bar reports whatsoever changes in the pick bounding box as you lot make changes. Modifier Keys
  
• Shift – Clicking a bespeak with the shift key adds a new point.
• Alt/Pick – Clicking a point with the Alt/Selection key deletes a point.

Apply the Polygon Choice Tool to measure the same grassy area of the park.

Freehand Selection Tool

The Freehand Choice Tool works just similar the Freehand line tool, except that when yous stop dragging the cursor, the beginning and end of the line connect to enclose an expanse.

Angle Tool

You lot've seen that you lot tin measure out angles with straight line selections, but they are ever measured relative to the 3 o'clock position. The Angle Tool allows y'all to measure angles from any position.

• To measure, the first click defines 1 ray, the 2d the vertex, and the third the other ray.
• As you select or modify an angle selection, the status bar unremarkably reads the interior angle 0° –90°, which is always positive.
• To read the exterior (reflex) angle (180° –360°, double-click the Angle Tool button and change the appropriate setting.

  

  
  
• Question—what is the interior angle between the two direct paths (1 at about 12 o'clock, the other at 8:30 position)

Indicate Tool

This tool selects unmarried points. Double-clicking the Point Tool button brings up this Betoken Tool dialog box.

Multi-Point Tool

The Multi-Point Tool selects (and numbers) multiple points in the same choice. Double-clicking this tool brings up the Add to Overlay dialog box, which you lot'll learn more than almost after.

Wand (Tracing) Tool

The Wand Tool creates a selection by tracing objects of uniform color or thresholded objects. To trace an object, either click inside almost the right border, or exterior almost the left border of the object. Double-clicking the Wand tool allows you to set the pixel value tolerance for the selections. (In other words, how close do the values of the adjacent pixels have to be to include them in the selection.)

Your Consignment: Utilise Selection Techniques to Analyze an Image

1. Go to the Earth Observatory and download an image of involvement to you lot.
2. Spatially calibrate the prototype (set a scale).
3. Use one of the selection techniques you accept learned virtually to investigate features in the image.
4. Next, measure out one or more than significant features.
5. When you are finished, post the image to the Function 1: Share and Talk over Folio. Then draw the choice technique yous used and what yous analyzed.
6. Engage in an online give-and-take, sharing your ideas well-nigh using choice techniques in your teaching.

Source

^oneAdjusted from Earth Exploration Toolbook affiliate instructions under Artistic Eatables license Attribution-NonCommercial-ShareAlike 1.0.
²Adapted from Eyes in the Sky Ii online course materials, Copyright 2010, TERC. All rights reserved.
³New textile developed for World Analysis Techniques, Copyright 2011, TERC. All rights reserved.

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Source: https://serc.carleton.edu/earth_analysis/image_analysis/advanced/day_3_part_1.html

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