pHYs holds whole pixels per metre, so 300 ppi is stored as 11811 and
read back as 299.9994 (72 as 72.009). The ppi read is now the whole
number that rounds to the stored value when there is one, as Photoshop
reads it; other values stay as they are.
Fixes#4855
Exports copied the source EXIF with only Orientation and resolution
patched, so a camera JPEG's embedded thumbnail (IFD1) came along. Finder,
Android and upload pickers show that thumbnail instead of decoding the
image, so an edited photo kept its original preview.
export_exif now clears IFD0's next-IFD pointer, unlinking IFD1. Nothing
else moves, so every other offset stays valid; JPEG, PNG, WebP and the PSD
EXIF resource all go through it.
Co-authored-by: vivekprojects-GIT <179340152+vivekprojects-GIT@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
A camera JPEG (e.g. Nikon D3200) records its resolution only in EXIF IFD0, so it
opened at 72 ppi instead of 300, and saving wrote JFIF 72 next to the source's
EXIF 300.
Reading: a JPEG takes the first usable of APP13 Photoshop ResolutionInfo
(0x03ED), XMP tiff:X/YResolution, EXIF IFD0 X/YResolution + ResolutionUnit
(2 inch, also when absent; 3 cm), and only then the JFIF density. That is the
order Photoshop resolves them in; JFIF comes last because cameras write EXIF
only while many tools write a default JFIF 72. Other formats (WebP, HEIF, PNG
without pHYs, ...) fall back to XMP then EXIF when they have no resolution of
their own. All parsing is bounds-checked; malformed data reads as no
resolution.
Writing: JPEG, PNG, WebP, TIFF (XMP), PSD and Save for Web JPEG rewrite the
EXIF/XMP resolution to the image's: RATIONAL values in place, ResolutionUnit 2,
and an entry that can't be rewritten safely is removed from IFD0 without moving
any other data.
Gert Pellin - GPE