How can I create a method in Java that rotates an image 90 degrees clockwise?

Question

This is what I have so far:

public static Photograph rotated(Photograph photo) {
    Photograph rotated_copy = new Photograph(photo.getHeight(), photo.getWidth());
    Pixel starting_pixel = photo.getPixel(0,0);

    for(int col = 0; col < photo.getWidth(); col++){
        for(int row = 0; row < photo.getHeight(); row++){
            starting_pixel = photo.getPixel(col,row);
            rotated_copy.setPixel(row, col, starting_pixel);
        }
    }
    return rotated_copy;
}

However, this method rotates any Photograph taken in 90 degrees counter-clockwise. How can I fix this?

90* counter-clockwise = x* clockwise. Find x and rethink the method. — Tdorno, Oct 23 '13 at 21:47
Are you sure this really rotates it by 90 degrees? It just switches all the row indexes with columns... For example pixel 0,0 stays on 0,0, right? — libik, Oct 23 '13 at 21:48
In fact, I think it just switches the picture with the center being the x=-y function... — libik, Oct 23 '13 at 21:50
Your code is not rotating the image; it is flipping the image (mirroring the image along the line where x=y). — Big Al, Oct 23 '13 at 21:50
Big Al is wrong, your code is indeed rotating. You've tested it, right? And the problem is counter-clockwise? So why are you listening to him saying its flipping? — SpacePrez, Oct 23 '13 at 21:51
Yeah Zaphod, I tested it and it's rotating counter-clockwise. — Pernicious Rage, Oct 23 '13 at 21:53
I think here is your response: http://stackoverflow.com/questions/12165977/java-image-rotation — promanski, Oct 23 '13 at 21:54
@Zaphod42 No, it's not rotating. The element at `[0][0]` always remains the same and also the element at `[rowscount][colscount]`. Take a look at [this IDEOne example with a simple int array](http://ideone.com/unxMJ6) — BackSlash, Oct 23 '13 at 21:55
@AliAlamiri the actual object implementation does not matter. You can do getPixel and setPixel with BufferedImage too. BufferedImage may have a convenient rotate method, but his point still stands. — SpacePrez, Oct 23 '13 at 21:59
"Ah crap Big Al. In that case, how would I make it rotate" ... you think its rotate because it changes the picture, but `it does not rotate` it switch the picture with x=-y function as center — libik, Oct 23 '13 at 22:01
Yeah, its actually mirroring the image across both axis, which makes it seem almost like its rotating but it isn't. I've modified my answer to point him in the right direction. — SpacePrez, Oct 23 '13 at 22:06

Maciej Stachowski · Accepted Answer · 2013-10-23T22:03:24.950

1

public static Photograph rotated(Photograph photo) {
    Photograph rotated_copy = new Photograph(photo.getHeight(), photo.getWidth());
    Pixel starting_pixel = photo.getPixel(0,0);

    for(int col = 0; col < photo.getWidth(); col++){
        for(int row = 0; row = photo.getHeight(); row++){
            starting_pixel = photo.getPixel(col,row);
            rotated_copy.setPixel(photo.getHeight() - row - 1, col, starting_pixel);
        }
    }
    return rotated_copy;
}

I think.

edited Oct 23 '13 at 22:03

answered Oct 23 '13 at 21:54

Maciej Stachowski

1,708
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lol, do you know that you did EXACTLY the same as the author but in different order? :) – libik Oct 23 '13 at 21:55
Corrected it now (hopefully this time it'll work - I know what to do, but my spatial imagination is kinda weak today ;) ) – Maciej Stachowski Oct 23 '13 at 22:06

SpacePrez · Answer 2 · 2013-10-23T22:07:06.003

0

EDIT: Hm, unfortunately that's close but doesn't quite work. Its reflecting the image while it rotates it. You could fix that though:

Instead of placing the co-ordinates in their opposite (X in Y and Y in X), you have to store them in a different order.

Think about the problem. After a 90' clockwise rotation, the co-ordinates (0,0) (0,HEIGHT) should become (0, HEIGHT), (WIDTH, 0) right?

So instead of:

starting_pixel = photo.getPixel(col,row);
rotated_copy.setPixel(row, col, starting_pixel);

you need something like

starting_pixel = photo.getPixel(col,row);
rotated_copy.setPixel(photo.getWidth() - row, col, starting_pixel);

edited Oct 23 '13 at 22:07

answered Oct 23 '13 at 21:55

SpacePrez

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Sry man, if you do it as "X becomes Y, Y becomes X", can you explain me, how the hell pixel on left top corner at {0,0} rotate to the right top corner {max_width,0} or to the left bottom corner {0,max_height}? :) – libik Oct 23 '13 at 21:57
@libik ah okay you're right, its both rotating and mirroring the image, so that's not quite right. I've modified my answer. – SpacePrez Oct 23 '13 at 22:02

How can I create a method in Java that rotates an image 90 degrees clockwise?

2 Answers2