XnView Software

XnViewMP 1.6.3
Windows11 (23H2), display resolution 3840x2160, dpi scale 150%

Browser - metadata - EXIF thumbnail
it is only possible to rotate and rebuild/remove embedded thumbnails,
it would be handy to have extract/replace actions as well

Suggestion

• add new commands for embedded thumbnail
  • extract
    exiftool -a -b -W FOLDERNAME/%f_%t%-c.%s -preview:all FILE
    exiftool -a -b -W %f_%t%-c.%s -preview:all test_img_thumbnail.jpg
  • replace
    exiftool '-ThumbnailImage<=SOURCE_FILE' TARGET_FILE
    exiftool '-ThumbnailImage<=new_thumb.jpg' target_img.jpg
    Note: to comply with standard, new thumbnail must be ≤64Kb
  • remove
    same as in Clean... dialog, eg
    exiftool -ThumbnailImage= FILE OR
    exiftool -ifd1:all= -ext jpg FILE
    check link for details

test image

ref

Format	Max Dimensions	Max Size (Bytes)	Notes
JPEG (EXIF)	160×120 typical, up to ~256×256	Up to ~60 KB (EXIF block ≤64 KB)	Stored as JPEG (usually) inside APP1/EXIF segment; larger ones get stripped
PNG	No defined thumbnail spec; custom or iTXt-based	Generally under 1 MB for compatibility	Thumbnails not standardized; apps may embed small PNG/JPEG chunks manually
WebP	Commonly 128×128 or 256×256	Around 50–100 KB recommended	Stored as separate image chunk in Extended WebP container
HEIC / AVIF	256–320 px (longest side typical)	Often under 150–200 KB	Thumbnails are separate image items inside the container
TIFF	128×128 to 256×256 typical	~64 KB if tied to EXIF limits	Often in SubIFD as JPEG or reduced RGB preview
PSD	256×256 to 512×512	Can be hundreds of KB	Stored as composite preview image inside file
RAW (CR2, NEF, etc.)	160×120 up to full-res preview	~64 KB for EXIF thumb, larger previews allowed	Thumbnail often small JPEG; medium/large preview may also be embedded

Related

• FAQ
  XnViewMP - thumbnails - understanding quality/size

• suggestion
  Metadata - EXIF thumbnail - add extract/replace actions (current post)