Description:
When exporting to PDF, you can choose the JPEG compression ratio (1%-100%) and force a fixed image resolution (DPI). It seems like LibreOffice isn't really compressing the JPEG image if a compression ratio >75% is chosen.

For example, the attached file (my cute son there!):
- Exporting to PDF at 100% compression ratio & 150DPI = PDF's size 1.741 Kb
- Exporting to PDF at  76% compression ratio & 150DPI = PDF's size 1.741 Kb
- Exporting to PDF at  75% compression ratio & 150DPI = PDF's size   101 Kb


Steps to Reproduce:
1.Open the attached file
2.Go to File → Export PDF...
3.Set the ratio compression on 76% and save
4.Repeat step 3. with ratio compression 75%


Actual Results:
Only after ratio compression is 75% or less, the JPEG deflating occurs


Expected Results:
We should see a shrinking of the resulting PDF size when increasing the compression ratio.


Reproducible: Always


User Profile Reset: No



Additional Info:
Version: 6.0.3.2
Build ID: 1:6.0.3-0ubuntu1
CPU threads: 2; OS: Linux 4.15; UI render: default; VCL: gtk3; 
Locale: ca-ES (en_US.UTF-8); Calc: group