Photo Exif data is removed when image is rotated #39

New Issue

aheathershaw · 2018-07-27T16:34:20+01:00

aheathershaw commented

2018-07-27 16:34:20 +01:00

I've recently discovered that the GD library removes Exif data from the image and replaces it with its own when an image is rotated and saved back out again.

Now we can "re-analyse" photos, we need the original Exif data available, so we shouldn't be modifying the original image.

Instead, the thumbnail generation should be looking at the Orientation flag, and rotating the thumbnail, not the original.

I've recently discovered that the GD library removes Exif data from the image and replaces it with its own when an image is rotated and saved back out again. Now we can "re-analyse" photos, we need the original Exif data available, so we shouldn't be modifying the original image. Instead, the thumbnail generation should be looking at the Orientation flag, and rotating the thumbnail, not the original.

aheathershaw added this to the Version 2.1.0 milestone 2018-07-27 16:34:20 +01:00

aheathershaw self-assigned this 2018-07-27 16:34:20 +01:00

aheathershaw added the

bug

label 2018-07-27 16:34:20 +01:00

aheathershaw commented

2018-07-27 16:34:34 +01:00

This also means when manually rotating/flipping images, we can't touch the original - only regenerate the thumbnails. When the original is viewed, we apply the transformations again stored in the database.

aheathershaw commented

2018-07-27 16:34:49 +01:00

After thinking this through a bit more, we now store the Exif data in MySQL (as of meta data V2) therefore as long as this data isn't overwritten during a re-analyse, we just use that instead of going back to the original image.

This minimises the changes as the rest of BT's behaviour can stay as it is now.

When an image is replaced, the stored Exif data must be removed and replaced with that from the new image.

After thinking this through a bit more, we now store the Exif data in MySQL (as of meta data V2) therefore as long as this data isn't overwritten during a re-analyse, we just use that instead of going back to the original image. This minimises the changes as the rest of BT's behaviour can stay as it is now. When an image is replaced, the stored Exif data must be removed and replaced with that from the new image.

aheathershaw commented

2018-07-27 16:34:58 +01:00

Any images that have been rotated (either manually or automatically using the Exif Orientation flag) must be re-uploaded using the new "replace image" function in 2.1 to restore the correct Exif data for future use/analysis.

aheathershaw closed this issue

2018-07-27 16:35:07 +01:00

aheathershaw commented

2018-07-27 16:35:22 +01:00

Migrated from https://github.com/andysh-uk/blue-twilight/issues/39

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