Clean app markers increases the image file size

[hor0124]

XnView: MP 1.11.5 - 64 bit
OS: Windows 11 25H2

I use GIMP to fix Some old images.
When I try to use the "clean all other markers" option (from the clean metadata function) the image file size increases
The image has no other metadata information.

I noted the same behaviour from files before I even edited them (right after I scanned the image.)

How can this be? shouldn't clean shrink the file (or at least keep it the same?)

[cday]

Are you able to post example 'Before' and 'After' files for someone to inspect?

[user0]

check your format write settings in Settings>Formats>Write

[hor0124]

Here is a simple example I created (don't be alarmed - it's a black rectangle).

[user0]

check 'Optimize Huffman table'

[hor0124]

Thanks user0.
May I ask that you specify what the setting should be instead of just saying "check".

Some more examples
Before - Copy (2) is fresh out of Gimp 3.24.
After - Copy (2) is after "cleaning" with 'Optimize Huffman table' turned on.

[user0]

there are 2 ways to remove metadata in XnViewMP

• in Viewer
  it only affects the loaded image, so the image must be saved (encoded) and Write settings will be used

• in Browser (your case)
  it does not re-encode image, so the bitstream should theoretically remain identical

However, it looks like XnViewMP uses jpegtran (from libJPEG/turbo) which affects bitsteam,
if you want to strip all metadata w/o touching bitstream - use exiftool

Test
test with your 2nd example file (1.28 KiB)

• XnViewMP OR jpegtran
  jpegtran -copy none -outfile 2_jpegtran.jpg 1.jpg
  Browser>Metadata>Clean... - all checkboxes, except huffman optimization
  4.97 KiB bitstream changed, APP0 remains
  
  jpegtran -copy none -optimize -outfile 2_jpegtran_optimize.jpg 1.jpg
  Browser>Metadata>Clean... - all checkboxes
  2.51 KiB bitstream changed, APP0 remains

• exiftool
  exiftool -all= -o 3_exiftool_all.jpg 1.jpg
  1.26 KiB bitstream unchanged, all metadata removed