How to rotate an array counter clockwise and invert it vertically?

Question

Say each pixel in this picture(fig 1) is an element in an array. How would I rotate it 90 degress counter-clockwise(fig 2) and invert it vertically(fig 3)?

figure 1: fig 1

figure 2: fig 2

figure 3: enter image description here

My current codes are:

private static Color[][] invert(Color[][] chunk){ //same as rotate
    Color[] temp;
    for(int i=0;i<chunk.length/2;i++){ //reverse the data
        temp=chunk[i];
        chunk[i]=chunk[chunk.length-i-1];
        chunk[chunk.length-i-1]=temp;
    }
    return chunk;
}

private static Color[][] rotate(Color[][] chunk){
    int cx = chunk.length;
    int cz = chunk[0].length;
    Color[][] rotated = new Color[cz][cx];
    for(int x=0;x<cx;++x){
        for(int z=0;z<cz;++z){
            rotated[z][x]=chunk[cz-z-1][x];
        }
    }
    return rotated;
}

The invert does the same function as the rotate though. Any help?

Baz · Accepted Answer · 2012-06-24 10:11:02Z

3

seems like you are trying to transpose the array (fig3 = transpose(fig1)).

use a double for loop and save in the entry [i][j] the value of [j][i].

see LINK for more information on the matrix transpose...

so all in all, you can use transpose to get fig3 and afterwards invert to get fig2.

edited Jun 24, 2012 at 10:11

answered Jun 24, 2012 at 9:50

Baz

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2 Comments

jocopa3 Over a year ago

Based on your answer I got: temp = chunk[i][j]; chunk[i][j]=chunk[j][i]; chunk[j][i] = temp; But it doesn't do anything different, the part is still the same. Help?

Baz Over a year ago

create a new array result and save the input[i][j] entry of the input array in the result[j][i] entry. don't work on the input array!

sideways8 · Accepted Answer · 2012-06-24 11:08:20Z

2

Baz is right, the transpose will get the job done. It looks like your transpose method used only the source array? If you looped through the whole of both lengths, you would undo all the work you did in the first half. This transpose method works for me:

public static Color[] [] transpose (Color[] [] a){
    int[] [] t = new Color [a [0].length] [a.length];
    for (int i = 0 ; i < a.length ; i++){
        for (int j = 0 ; j < a [0].length ; j++){
            t [j] [i] = a [i] [j];
        }
    }
    return t;
}

answered Jun 24, 2012 at 11:08

sideways8

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