Draw a Circle From the Center Imagej

Role 1: Practice Using Selection Techniques^three

Sometimes you lot're interested in manipulating or analyzing entire images, but information technology'southward more common to be interested in a only part of an epitome. Identifying the pixels you're interested is ane of the key tasks in image processing, and ImageJ provides a broad range of tools and techniques for making selections.. Another proper name for a choice is Region Of Interest or ROI. The phrase "select, then deed" is a cornerstone of many computer applications, and image processing is no exception.

In many cases, the instructions won't tell yous explicitly what to do, but we urge you to Attempt EVERYTHING YOURSELF! Option is such an important process that there are no fewer than xv split up tools on the ImageJ toolbar and over 20 menu items dedicated to selections. Your mastery of ImageJ depends largely on your ability to make and use selections.

If you take used other graphic software, you lot may be frustrated that you can't draw points, lines, shapes, and text with ImageJ. That's because the process of selecting is of primary importance, and cartoon is secondary. Information technology can exist done only information technology takes an extra step, which you'll learn about afterward.

Prepare a Selection Practice Image

You'll need an image to practice these option techniques on. We'll use this image of downtown Pasadena, California for most of our selections.

• Click this paradigm to open it as a total-size image. Right-click (PC) or command-click (Mac) the image to download it to your computer. And then, open the epitome in ImageJ using whatsoever of the techniques you've learned. For orientation, North is to the right.

If you open the l% reduced-resolution version below, features will be more difficult to see and the image calibration will be 1 meter per pixel, not 0.5 meters per pixel (2 pixels/meter).

Colors

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

• Foreground – The foreground color is the default color for cartoon, painting, and filling.
• Groundwork – The background color is the color used for erasing and deleting.
• Option – The choice colour is the color used to display selection outlines.
The foreground color, not the pick color is used to depict lines and shapes on the epitome.

Choose a Selection Colour

Selections are indicated by a colored outline. You take control over the color of the pick outline. If y'all have trouble seeing the choice on top of the image (blood-red on red, for example), you lot might desire to modify the option color to something that is easier to meet. The default selection color is yellow, but this tin be changed to any of 8 standard colors (blackness, white, red, dark-green, blue, cyan, magenta, yellowish, and orange).

• Choose Edit > Options > Colors and choose a choice color. (The default yellowish is expert—nosotros but wanted you to run into where to change it if you need to afterward.

  

  
  

Selection Tools

Accessing Option Tools and Tool Options

At any given time, eight selection tools are visible on the ImageJ toolbar. The tool buttons marked with small-scale red triangles comprise two or more related tools. To access the other tools, right-click (PC) or command-click (Mac) the tool button and select from the pop-up tool bill of fare.

Some selection tools have options, such as the width of line selections. At that place are usually two means to access these settings:

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

Select and de-select the unabridged image

The two nearly bones selections are to select everything and select zilch. In a foreign twist of logic, both of these options usually produce the aforementioned results. When cypher is selected in an image, most operations assume that you desire to use the entire image (ALL of the pixels). Operations that require a pick generally display an alert message to that effect.

• If necessary, zoom out and then yous can come across the entire epitome on your monitor. The piece of cake way to fit your image to your monitor is to double-click the magnifying glass tool on the ImageJ toolbar. (This is of import because if you can't run into the edges of the prototype y'all won't see the xanthous outline around the image when it's selected.)
• Cull Edit > Selection > Select All. You should see a xanthous choice outline around the outer border of the image.
You may know that you lot can cancel a option past clicking anywhere outside the option. When the whole image is selected, there is no "outside". The only way to cancel the selection is to de-select the image, or to "select none" of the pixels.
• Choose Edit > Selection > Deselect All – The yellow choice outline should be gone.
Remember, if yous are zoomed in on one role of the image, at that place may be a selection outline somewhere that y'all can't encounter. When in doubt, use Select None to cancel all selections.

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

• Try these shortcuts out. (Notation: Keyboard shortcuts piece of work except when yous're entering text using the text tool, for obvious reasons.)
• Before standing, make certain zippo is selected.

Line Tools – Direct Line Pick

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

• Apply the Straight Line pick tool to make a straight line pick anywhere in the middle of the paradigm. As you drag your pick, the ImageJ status bar shows the length of the line and its angle measured ±180° from the 3 o'clock position (0°). Positive angles are measured counterclockwise from 0° to 180° and negative angles are measured clockwise from 0° to -180°.
  
• The pocket-sized white boxes at the center and ends of the line choice are handles. Drag the eye handle to motion the option without irresolute its length or bending.
• Drag either end handle to move that terminate of the selection while the other end remains fixed.
• Directly line selections tin can be dragged beyond the boundaries of the paradigm window.
  Modifier Keys
  • Shift – Constrains the line choice to horizontal or vertical. (Very useful when setting the scale.)
  • Alt/Option – When dragging an end handle, this keeps the line length stock-still while changing the angle. (AKA "Radar" manner)
  • Ctrl/Command – Drag either finish of the line to rotate it about its middle and change its length symmetrically. (AKA "Propeller" manner) When you are zoomed in on an prototype, this modifier forces the ends of the line to first and stop on whole number pixel coordinate values (try it to encounter what this ways).
  • Arrow Keys – The four arrow keys are used to "nudge" selections 1 pixel at a time to the left, right, up, and down. (This is the merely time nudging will be mentioned, but remember that information technology works for ALL selections. It does not, however, let you movement whatsoever part of a pick outside the boundaries of the image. When in that location is no agile selection, the upwardly and downward arrows function as "zoom in" and "zoom out" shortcuts.)
• Test each of these modifiers separately and in combinations. (not all combinations volition piece of work). For example, can you exercise both "radar" and "propeller" modes at the aforementioned time? How about all three?
• Open the gel sample paradigm (File > Open Samples > Gel).
• Employ the directly line selection tool to select a vertical line downward the center of the 3rd lane from the left.
• Choose Analyze > Plot Contour.
• Double-click the directly line pick tool push button on the ImageJ toolbar to open the Line Width dialog box, and set the line width to 20.
• Activate the gel.gif image window and make another profile plot. Compare the two plots made from unlike width line selections.
• Set the line width back to 1 pixel.
• Shut the gel, plot, and Line Width windows.
• Returning to the Pasadena aerial image, set the scale (spatial calibration) for this image using the directly line choice tool to measure the width of the expressway overpass (bottom right) at the place where it crosses the center of the freeway. The width of the overpass is 33 meters. (Tip: Zoom in to the overpass earlier selecting information technology, and use the shift central to force the line to be vertical.)
• Bank check your spatial calibration by measuring the long dimension of the parking structure in the lower left quadrant of the epitome.
• Practise yous see the remains of a helipad toward the left cease of the parking structure? Standard helipad markings are a circumvolve or foursquare 15 meters across. Do these markings encounter the standard?

Line Tools – Segmented Line Selection

Segmented line selections are used for the same purposes as straight lines. Do NOT, yet, use the segmented line tool to make polygon area selections. There is a dissimilar tool for that purpose.

• Correct-click (PC) or command-click (Mac) the line selection tool on the ImageJ toolbar and choose the Segmented Line option tool from the pop-up tool menu.
• Create a segmented line selection anywhere on the Pasadena image.
Each click defines a new line segment. Every bit yous are selecting, the ImageJ status bar shows the length and angle of the current segment. To stop the selection, either double-click the last endpoint or click in the modest box at the beginning of the line selection. (Don't worry, this won't connect the two ends of the selection.)
• Once selected, the handles at each vertex of the line can be dragged to new locations to refine the selection. If y'all accidentally click too far from a vertex and the option disappears, utilize the Restore Pick command.
• To move a segmented line choice, movement the cursor over the choice until it becomes an arrow, then elevate. Segmented line selections tin exist dragged beyond the boundaries of the image window. As you drag, the status bar reports information about the bounding box of the selection (the smallest rectangle to completely contain the option): center (x,y), size (due west,h), and aspect ratio (ar). Attribute ratio is simply the ratio of the width to the elevation of the box. An attribute ratio of 2.5 means that the width is 2 and a half times the elevation.
  Modifier Keys
  • Shift – Shift-click a handle to split it into ii separate handles to add more detail to the selection.
  • Alt/Selection – Alt- or Option-click a handle to delete it.
• Test each of these modifiers before continuing to the adjacent tool.

Line Tools – Freehand Line Choice

Freehand line selections are used for the same purposes as straight and segmented lines. Don't use the Freehand Line tool to brand freehand area selections—there 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, simply click and drag the cursor effectually the paradigm.
• To move a freehand line selection, motility the cursor over the option until information technology becomes an arrow, then elevate.
• Freehand line selections can exist dragged beyond the boundaries of the image window. As you lot drag, the status bar reports information about the bounding box of the selection.
• Modifier keys have no result on freehand line selections.

Line Tools – Arrow Tool

Arrow selections are used for annotating (marker and labeling) images. You'll learn how to draw arrows and other shapes later on. For now, only exercise making arrow selections.

• Right-click (PC) or control-click (Mac) the line selection tool on the ImageJ toolbar and choose the Pointer Tool from the pop-upwards tool card.
• Double-click the Arrow Tool push button to open the Arrow Tool dialog box.

  

  
  
• The Arrow Tool dialog box lets you set the width (of the line), size (of the head), color, and fashion (of the head) of arrows. You can too 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 pop-up tool bill of fare.
• Create a rectangular selection anywhere on the Pasadena image. The normal selection way is to elevate from one corner of the rectangle to the contrary corner, in any management.
• Every bit you lot select or modify rectangles, the condition 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 exist dragged to refine the selection. If you accidentally click too far from a handle and the selection disappears, utilize the Restore Choice command.
• To move a rectangular selection, motion the cursor over the selection until information technology becomes an arrow, then drag. Rectangular line selections can exist dragged across the boundaries of the image window.
  Modifier Keys
  • Shift – Constrains the choice to a square.
  • Alt/Choice – After selecting, hold down the Alt or Pick key to change the width and height by one pixel at a time using the iv pointer keys. Only the lesser and right sides of the selection move. Watch the changing peak, width, and aspect ratio in the ImageJ condition bar.
  • Command (Mac)/Control (PC) – Draws or resizes rectangle from the middle.
  • Shift – Constrains the selection to a foursquare.
  • Command-Option (Mac)/Control-Alt (PC) – Maintains the current aspect ratio as the foursquare is resized.
  • Predict what will happen if you make a rectangular selection belongings down the Command-Shift (Mac) or Control-Shift (PC) keys.
  • Select and mensurate the area of the rectangular block containing the park and flat buildings.
• Test each of these modifiers earlier continuing to the next tool.

Rounded Rectangle Tool

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

• Right-click (PC) or control-click (Mac) the Rectangle selection tool on the ImageJ toolbar and choose the Rounded Rectangle Tool from the pop-upward tool menu.
• 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 the tool'due south options dialog box.

  

  
  
• Do making rounded rectangle selections using dissimilar corner diameters, stroke (line) widths, colors, and fills earlier continuing to the adjacent tool.

Oval Selections Tool

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

• The condition bar reports the coordinates, dimensions, and aspect ratio of the oval selection's bounding box.
• Elevate the oval option handles to refine the option.

Elliptical Selections Tool

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

• No information is reported in the status bar for elliptical selections.
• Drag the elliptical choice handles to refine the choice. If you accidentally click too far from a handle and the selection disappears, employ the Restore Pick command.
• Use either the Oval or the Elliptical Selection Tool to mensurate the area of the round parking expanse on the middle left edge of the block containing the park. (Hint: Apply the modifier keys to select a circumvolve from the eye out.)

Selection Castor Tool

The Choice Brush Tool lets you create or adjust a choice using a circular "brush". This tool is peculiarly useful for touching upwards selections and for making visual selections of regions that don't accept distinctive geometric or color characteristics.

• Moving the brush from outside an existing selection into the selection shrinks (subtracts from), moving the brush from inside the selection out expands (adds to) the selection.
• The status bar reports any changes in the selection bounding box every bit you brand changes.
• The brush diameter tin be adjusted by double-clicking the Castor Selection Tool push button on the ImageJ toolbar.

  

  
  Modifier Keys
  
• Shift – Always add together the brush to the pick.
• Alt/Choice – Always subtract the brush from the option.

Use the Selection Brush Tool to measure out the largest grassy area of the park (bounded by sidewalks). Where the trees are in the way, assume there is grass under them, right up to the edges of the sidewalks.

Polygon Choice 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 concluding point or click in the small box at the outset of the first side of the polygon.

• Vertices are handles that can exist moved.
• The status bar reports any changes in the selection bounding box as y'all brand changes. Modifier Keys
  
• Shift – Clicking a indicate with the shift key adds a new point.
• Alt/Choice – Clicking a indicate with the Alt/Pick key deletes a point.

Utilize the Polygon Pick Tool to measure the same grassy area of the park.

Freehand Pick Tool

The Freehand Selection Tool works only like the Freehand line tool, except that when you stop dragging the cursor, the beginning and end of the line connect to enclose an surface area.

Bending Tool

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

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

  

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

Signal Tool

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

Multi-Indicate Tool

The Multi-Bespeak Tool selects (and numbers) multiple points in the same selection. Double-clicking this tool brings upwards the Add together to Overlay dialog box, which you'll learn more almost after.

Wand (Tracing) Tool

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

Your Assignment: Use Selection Techniques to Analyze an Paradigm

1. Go to the Globe Observatory and download an image of interest to you.
2. Spatially calibrate the image (set a calibration).
3. Use one of the selection techniques y'all take learned about to investigate features in the image.
4. Adjacent, measure one or more meaning features.
5. When you are finished, mail service the prototype to the Part ane: Share and Discuss Folio. Then describe the choice technique y'all used and what y'all analyzed.
6. Engage in an online discussion, sharing your ideas about using selection techniques in your teaching.

Source

^aneAdjusted from World Exploration Toolbook chapter instructions under Creative Commons license Attribution-NonCommercial-ShareAlike i.0.
²Adjusted from Eyes in the Sky II online form materials, Copyright 2010, TERC. All rights reserved.
³New cloth adult for Earth 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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