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4.1 Image view window

Figure 4.1 shows nip's image view window.

Figure 4.1: The image view window
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If you press i with the keyboard focus on the image you will zoom in on the pixel your mouse pointer is over. Press o to zoom out again, or press the number keys 1, 2, 4 and 8 to jump straight to a particular magnification. If you hold down the Ctrl key while pressing these numbers, nip will zoom out by that amount. If you press 0 (the number zero), then nip will pick a magnification or reduction which fits the image to the size of the window.

When the image is too large for the window, you can use the scroll bars to move about the image. With the keyboard focus on the image the cursor keys left, right, up and down move a few pixels in each direction; hold down Shift as well to move a screenful at a time; hold down Ctrl as well to jump to the extreme edges of the image. You can also drag with the middle mouse button to pan around the image.

Use the View menu to add extra elements to the window. You can turn the status bar on and off, and you can add a display control bar and a set of rulers to the window. You can control which window elements appear by default with the settings in the Preferences workspace, in the Image display column.

The zoom and the position controls can also be accessed through an additional tool menu which appears when you click the right mouse button, see Figure 4.2. This menu controls the action of the left mouse button and gives five options.

Figure 4.2: Image tool menu
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The status bar shows the type of image you are looking at, see Figure 4.3. In this case, the image has just one band (it's monochrome), each pixel in the image is a 8-bit unsigned integer, the image has 1862 by 2360 pixels, it occupies 4.19 megabytes, and it has a resolution of 1.45 pixels per millimetre.

The second line shows that the mouse was at position 816 pixels from the left of the image, and 456 pixels down from the top of the image. The pixel at that position has the value 8. Finally, the figure at the bottom right shows that you are currently viewing with a magnification of 1:4, that is, for every display pixel there are four image pixels.

Figure 4.3: The status bar
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Figure 4.4: The display control bar
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If you select View=>Show display control bar, nip will add a bar to the top of the window which you can use to change the contrast and brightness of the image you are viewing. The left-hand slider and text box set the gain for the image: each pixel is multiplied by this amount before display. The right-hand slider and text box set the offset: each pixel has this value added to it before display. This is useful for boosting the brightness in dark areas of images.

Figure 4.5: The display control bar menu
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If you click the left mouse button on the arrow to the left of the display control bar, nip pops up a menu of useful display functions -- see Figure 4.5.

Scale searches the area of the image you are viewing for the darkest and brightest points and chooses settings for the gain and offset sliders which will stretch the image to use the full range of your screen. False colour works only for monochrome images: it tries to make small differences in brightness more visible by colour-coding them.

Interpret determines how nip displays colorimetric images. If this option is turned on (it is by default), then nip will look at the Type field in the image header, and try to transform the image to a viewable form for you. This is usually the behaviour you want. Reset moves the sliders back to the default positions of 1.0 and 0.0. Finally, Hide removes this display control bar.

Figure 4.6: Image rulers
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If you select View=>Show rulers, nip will add rulers to the edges of the window which you can use to measure numbers of pixels, see Figure 4.6. If you left-drag from the ruler, you can create a guide. Guides are useful for lining up other things in the view window.

The File menu contains two useful items: select Replace image to change the image which is being displayed in the window. Select Save image to save the image you are viewing to a file. See §4.3 for details on nip's load and save dialogs. The New menu is a no-mouse route for creating regions, points, guides and arrows.

If you select View=>Show paint bar (or select the paintbrush from the right-button menu), nip adds a paint bar to the top of the window. You can use the paint bar to do simple edits to the image being displayed. See Figure 4.7.

While the paint bar is very limited, it does have two useful features. First, it can paint with any pixel value, even complex. For example you can take the fourier transform of an image and paint out the peaks. Second, it doesn't operate on a memory copy of an image, it operates directly on the file on disc. This means that you can paint on images of any size, but it does make the paint bar a bit dangerous.

Normally paint actions are live, that is, every time you paint something all the objects which depend on the thing you painted will recalculate. This can sometimes cause annoying delays: there's a preferences option to turn off automatic recalculations for the paint bar.

Figure 4.7: The paint bar
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The Undo and Redo buttons move forward and back though paint actions. The Clear button wipes the undo/redo history (useful if memory is getting low). There's an option in the preferences workspace which controls the number of undo steps nip tracks.

The Tool menu sets the surrent paint mode. Most are obvious: Dropper lets you pick a new value for the Ink (this will work for any image type: you can have complex ink, for example). Flood fills while pixels are different from the ink value, Flood blob fills with ink while pixels equal the pixel you clicked to start the flood. If you add guides to the image window, the paint tools will all snap to the nearest guide.

Double-click on the ink box to pick a new colour in RGB space. You can drag and drop ink colours from other paint bars, or from colour widgets in nip's main workspace. Click on the font button to chose a font for the text tool. Enter the text that the text tool is to draw in the box at the far right of the paint bar.


next up previous contents
Next: 4.2 Regions, points, arrows Up: 4. Reference Previous: 4. Reference   Contents
John Cupitt 2003-07-21