Rotate images according to EXIF info

Some digital cameras are saving the snapshots as they come from the digital sensor. This is not always the right orientation, as it depends on how you are position the camera. Luckily, the cameras are also saving the orientation information into EXIF attributes.
This article is about how to automatically correct this from your Java program, using jMagick. The entire thing can be break down into pieces: read an EXIF attribute for an image, interpret the value and transform the image.
The EXIF attribute responsible for orientation is called Orientation. According to EXIF specs, the values have the following meaning:

• 1 = The 0th row is at the visual top of the image, and the 0th column is the visual left-hand side.
• 2 = The 0th row is at the visual top of the image, and the 0th column is the visual right-hand side.
• 3 = The 0th row is at the visual bottom of the image, and the 0th column is the visual right-hand side.
• 4 = The 0th row is at the visual bottom of the image, and the 0th column is the visual left-hand side.
• 5 = The 0th row is the visual left-hand side of the image, and the 0th column is the visual top.
• 6 = The 0th row is the visual right-hand side of the image, and the 0th column is the visual top.
• 7 = The 0th row is the visual right-hand side of the image, and the 0th column is the visual bottom.
• 8 = The 0th row is the visual left-hand side of the image, and the 0th column is the visual bottom.
• Other = reserved

Graphically, this looks like this: .
The following transformations should be applied to the images according to their EXIF orientation:

Autorotate EXIF images

where the possible operations are horizontal or vertical flip and rotate (90 degrees clockwise or counter-clockwise and 180 degrees). The corresponding jMagick methods from MagickImage class are:

• horizontal flip – flip()
• vertical flip – flop()
• rotate 180 degrees – rotate(180)
• rotate 90 degrees clockwise – rotate(90)
• rotate 90 degrees counter-clockwise – rotate(-90)

Now let’s translate everything into Java code:

private static final int NONE = 0;
private static final int HORIZONTAL = 1;
private static final int VERTICAL = 2;
private static final int[][] OPERATIONS = new int[][] {
        new int[] {  0, NONE},
        new int[] {  0, HORIZONTAL},
        new int[] {180, NONE},
        new int[] {  0, VERTICAL},
        new int[] { 90, HORIZONTAL},
        new int[] { 90, NONE},
        new int[] {-90, HORIZONTAL},
        new int[] {-90, NONE},
        };

public static MagickImage rotateByExif(MagickImage image) throws MagickException {
    try {
        int index = Integer.parseInt(image.getImageAttribute("EXIF:Orientation")) - 1;
        int degrees = OPERATIONS[index][0];
        if (degrees != 0)
            image = image.rotateImage(degrees);
        switch (OPERATIONS[index][1]) {
            case HORIZONTAL:
                image = image.flopImage();
                break;
            case VERTICAL:
                image = image.flipImage();
        }
    }
    catch (NumberFormatException exc) {}
    catch (NullPointerException exc) {}
    return image;
}

Now you can simply call the rotateByExif method. For more information on how you can use jMagick to load and save images please see the official documentation or see Watermark with jMagick article. Actually you can even integrate this, so that you apply it to the watermarked images.

So actually it is pretty simple to rotate images according to the EXIF info using jMagick: just get the EXIF Orientation attribute with getImageAttribute() method and, according to its value, apply the rotateImage, flipImage and flopImage.