Apply correct rotation depending on EXIF orientation code

[taboulot]

Describe the bug On some images, the 90 degree rotation is not correctly applied (or any other rotation).

To Reproduce Steps to reproduce the behavior:

1. In the example app, in function resize put a value of 90 in rotation parameter
2. Build the example application;
3. Select an image with a EXIF orientation code = 4 (see explanation below)

Observed behavior	original	result

Expected behavior	original	result

Platform concerned:

• Android: ✅
• iOS: ✅

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Details

Current behavior

Before applying any transformation to the image, the library do two things:

1. Load the bitmap image = a grid of dots or pixels that forms an image = raw image of the camera sensor
2. Get the orientation of that image following the EXIF orientation code;
3. Add the rotation if parameter is specified;
4. Apply the rotation to the bitmap;
5. Apply the resizing to the bitmap;
6. Save the new image.

Problem

We do not handle properly all EXIF Orientation code. In the case of an Orientation code = 4 (i.e Mirror vertical), the getOrientation method returns 0, which is correct, but we do not apply a vertical flip on the bitmap before applying the desired rotation.

The EXIF Orientation code tells to the device how the image (orientation + flip) should be displayed on the screen (i.e. how the bitmap should be displayed) => more information about each value here

The following array show which EXIF orientation value are & are not properly handled with a rotation of 90°:

Proposition of algorithm

1. Load the bitmap image = a grid of dots or pixels that forms an image = raw image of the camera sensor
2. Get the orientation of that image following the EXIF orientation code;
3. Get the flip (horizontal, vertical or none) of that image following the EXIF orientation code;
4. Apply the rotation to the bitmap;
5. Apply the flip to the bitmap;
6. Apply the rotation if parameter is specified;
7. Apply the resizing to the bitmap;
8. Save the new image.

[taboulot]

I do not have at the moment any time to implement it. Any help is welcome.

[retyui]

you can find more images with Exif for testing https://github.com/recurser/exif-orientation-examples

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[stale[bot]]

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