Exif issues in pictures captured with the GrapheneOS Camera

uniquecamel

About a month ago I switched to GrapheneOS from an iPhone and the experience has been pretty great overall. Still learning and discovering stuff and will probably have more questions and thoughts later on.

In this post I want to specifically discuss some Exif issues in pictures captured by the Camera app. I checked the Exif details with ExifTool and ran a validation command that checks potential problems with the metadata or inaccuracies according to the spec. Exiftool -a -validate -warning IMG.jpg. The command reported quite a lot of warnings concerning non conformance with the Exif specification.

Some tags are out of order - Exif tags are supposed to be in order based on the tag ID.
Some tags have odd offsets - according to the Exif specification all offsets have to be even and this is achieved by adding a null byte if necessary.
Some tags have the wrong format (Type) - those are 0x9000 ExifVersion which is ASCII/String (0x0002) but supposed to be UNDEFINED (0x0007) and 0x9208 LightSource which is LONG/int32u (0x0004) but supposed to be SHORT/int16u (0x0003).
Some mandatory tags are missing - those include 0x0213 YCbCrPositioning, 0x9101 ComponentsConfiguration and 0xa001 ColorSpace.
Some tags that are present require a higher Exif Version - the ExifVersion tag in the pictures is 0220, but 0x9010 OffsetTime, 0x9011 OffsetTimeOriginal and 0x9012 OffsetTimeDigitized require ExifVersion 0231 or higher. The newest version is 0300 but it is not widely used yet, most modern cameras use 0232.
Some tags are not allowed in JPEG files - those are 0x0100 ImageWidth and 0x0101 ImageHeight. They are intended for TIFF files and are not allowed in JPEGs because a JPEG marker is used instead of them.

I don't know how the camera app creates the Exif data in JPEG files and I'm not a programmer but could those warnings be fixed to conform to the Exif spec?

In addition to this, pictures captured with the Camera app have a APP0 JFIF segment after the APP1 Exif segment. This is redundant and a conflict between two standards, Exif and JFIF. Exif files are not supposed to have JFIF tags and vice versa.

Another suggestion if I may: When enabling the option to remove Exif data after capture, maybe keep, in addition to the 0x0112 Orientation tag, all of the mandatory tags according to the spec. Those tags are not sensitive and some provide useful information for image viewing software. The tags are 0x011A XResolution (no longer mandatory in version 0300), 0x011B YResolution (no longer mandatory in version 0300), 0x0128 ResolutionUnit (no longer mandatory in version 0300), 0x0213 YCbCrPositioning, 0x9000 ExifVersion, 0x9101 ComponentsConfiguration, 0xA000 FlashpixVersion (no longer mandatory in version 0300), 0xA001 ColorSpace, 0xA002 PixelXDimension, 0xA003 PixelYDimension.

akc3n

uniquecamel
These warnings won't prevent normal usage of the image and there's lots of EXIF tags that're "required" by spec, which don't have any real effect whether the image can be read or not.

Toggling off the default setting, 'Remove EXIF data after capture' under 'More settings' in the Camera app and executing exiftool -validate -warning -error -a IMG-exif.jpg will result in:

Validate                        : 13 Warnings (4 minor)
Warning                         : Non-standard format (int32u) for ExifIFD 0x9208 LightSource
Warning                         : Entries in IFD0 are out of order
Warning                         : Non-standard format (int32u) for IFD0 0x0112 Orientation
Warning                         : Tag ID 0x0112 Orientation out of sequence in IFD0
Warning                         : [minor] Unknown value for IFD0:Orientation
Warning                         : Missing required JPEG ExifIFD tag 0x9000 ExifVersion
Warning                         : Missing required JPEG ExifIFD tag 0x9101 ComponentsConfiguration
Warning                         : Missing required JPEG ExifIFD tag 0xa001 ColorSpace
Warning                         : Missing required JPEG ExifIFD tag 0xa002 ExifImageWidth
Warning                         : Missing required JPEG ExifIFD tag 0xa003 ExifImageHeight
Warning                         : [minor] IFD0 tag 0x0100 ImageWidth is not allowed in JPEG
Warning                         : [minor] IFD0 tag 0x0101 ImageHeight is not allowed in JPEG
Warning                         : [minor] Missing required JPEG IFD0 tag 0x0213 YCbCrPositioning

You can then do exiftool -ext jpg -all= --icc_profile:all -tagsfromfile @ -colorspacetags IMG-exif.jpg, followed by

$ exiftool -validate -warning -error -a IMG-exif.jpg
> Validate                        : OK

Note: this will create a backup of the original file, IMG-exif.jpg_original

You can see the difference by running:
exiftool -ee3 -U -G3:1 -api requestall=3 -api largefilesupport -time:all -gps:all -thumbnail3 -json -struct -n -v2 IMG-exif.jpg_original
or for a less detailed break down of everything, run:
exiftool -ee3 -U -G3:1 -api requestall=3 -api largefilesupport IMG-exif.jpg_original
and compare it by running those two commands by replacing the IMG-exif.jpg_original with IMG-exif.jpg.
Or comparing via exiftool -u IMG-exif.jpg -diff IMG-exif.jpg_original and this can be used below afterwards as well to compare, exiftool -u IMG-exif-removeall.jpg -diff IMG-exif.jpg_original

You can completely remove all the metadata with (backup the modified jpeg):
cp IMG-exif.jpg IMG-exif-removeall.jpg && exiftool -all= IMG-exif-removeall.jpg
which will show different results when running:
exiftool -ee3 -U -G3:1 -api requestall=3 -api largefilesupport -time:all -gps:all -thumbnail3 -json -struct -n -v2 IMG-exif-removeall.jpg
or:
exiftool -ee3 -U -G3:1 -api requestall=3 -api largefilesupport IMG-exif-removeall.jpg

The end result will be the same

$ exiftool -validate -warning -error -a IMG-exif-removeall.jpg
> Validate                        : OK

The point is none of that validating stuff matters when it comes to viewing the image for the general masses.
You can experiment by re-enabling the setting back to it's default placement in the Camera app and the only result that will be returned when validating it:

Validate                        : 1 Warning
Warning                         : Missing required JPEG IFD0 tag 0x0213 YCbCrPositioning

See https://grapheneos.org/usage#camera

By default, EXIF metadata is stripped for captured images and only includes the orientation. Stripping metadata for videos is planned but not supported yet. Orientation metadata isn't stripped since it's fully visible from how the image is displayed so it doesn't count as hidden metadata and is needed for proper display. You can toggle off stripping EXIF metadata in the More Settings menu opened from the settings dialog. Disabling metadata stripping will leave the timestamp, phone model, exposure configuration and other metadata. Location tagging is disabled by default and won't be stripped if you enable it.

EDIT: Additionally, I just came across this, https://exiftool.org/forum/index.php?topic=17124.msg91799#msg91799 and the Admin user of the exiftool forum answers your concerns as well.

uniquecamel

akc3n
Thank you for your response.
Yes, I know those warnings don't effect the image itself, and to be fair, also the pixel camera pictures report warnings. It's just that I like the Exif data to be "correct" I guess. Not a major issue by any means. I will probably just run an exiftool command on the pictures, I've come up with a slightly different one than yours: exiftool -P -all= --icc_profile:all -tagsfromfile @ -all:all -unsafe --jfif:all -exifversion=0232 -colorspace#=1 path/to/files

I'm curious, how does the GrapheneOS camera creates the Exif data? On GitHub it says that the app is based on "Android's modern CameraX library", so is the Exif handled by this library or is it handled by code developed by GrapheneOS directly?