CanvasResizer.java

package ij.plugin;
import ij.*;
import ij.plugin.filter.*;
import ij.process.*;
import ij.gui.*;
import java.awt.*;

public class CanvasResizer implements PlugIn {
    boolean zeroFill = Prefs.get("resizer.zero", false);

    public void run(String arg) {
        int wOld, hOld, wNew, hNew;

        ImagePlus imp = IJ.getImage();
        wOld = imp.getWidth();
        hOld = imp.getHeight();

        String[] sPositions = {
            "Top-Left", "Top-Center", "Top-Right", 
            "Center-Left", "Center", "Center-Right",
            "Bottom-Left", "Bottom-Center", "Bottom-Right"
        };
            
        String strTitle = "Resize Image Canvas";
        GenericDialog gd = new GenericDialog(strTitle);
        gd.addNumericField("Width:", wOld, 0, 5, "pixels");
        gd.addNumericField("Height:", hOld, 0, 5, "pixels");
        gd.addChoice("Position:", sPositions, sPositions[4]);
        gd.addCheckbox("Zero Fill", zeroFill);
        gd.showDialog();
        if (gd.wasCanceled())
            return;
            
        wNew = (int)gd.getNextNumber();
        hNew = (int)gd.getNextNumber();
        int iPos = gd.getNextChoiceIndex();
        zeroFill = gd.getNextBoolean();
        Prefs.set("resizer.zero", zeroFill);
        
        int xOff, yOff;
        int xC = (wNew - wOld)/2;   // offset for centered
        int xR = (wNew - wOld);     // offset for right
        int yC = (hNew - hOld)/2;   // offset for centered
        int yB = (hNew - hOld);     // offset for bottom
        
        switch(iPos) {
        case 0: // TL
            xOff=0; yOff=0; break;
        case 1: // TC
            xOff=xC; yOff=0; break;
        case 2: // TR
            xOff=xR; yOff=0; break;
        case 3: // CL
            xOff=0; yOff=yC; break;
        case 4: // C
            xOff=xC; yOff=yC; break;
        case 5: // CR
            xOff=xR; yOff=yC; break;
        case 6: // BL
            xOff=0; yOff=yB; break;
        case 7: // BC
            xOff=xC; yOff=yB; break;
        case 8: // BR
            xOff=xR; yOff=yB; break;
        default: // center
            xOff=xC; yOff=yC; break;
        }
        
        Undo.setup(Undo.COMPOUND_FILTER, imp);
        ImageProcessor newIP = expandImage(imp.getProcessor(), wNew, hNew, xOff, yOff);
        imp.setProcessor(null, newIP);
        Undo.setup(Undo.COMPOUND_FILTER_DONE, imp);
    }
    
    public ImageProcessor expandImage(ImageProcessor ipOld, int wNew, int hNew, int xOff, int yOff) {
        ImageProcessor ipNew = ipOld.createProcessor(wNew, hNew);
        if (zeroFill)
            ipNew.setValue(0.0);
        else 
            ipNew.setColor(Toolbar.getBackgroundColor());
        ipNew.fill();
        ipNew.insert(ipOld, xOff, yOff);
        return ipNew;
    }

}