Why do JPEGs exported from GIMP become much larger than the originals?
Asked 9/21/2020
1 views
2 answers
0
I edited some vacation photos in GIMP that were originally shot as JPEGs on an older digital camera. After adjusting levels and using auto color enhancement, the exported JPEGs became much larger — files that were under 3 MB are now 10 MB or more.
What causes this increase in file size? Is it due to the edits themselves, GIMP’s JPEG export settings, or both? And is there a way to keep file sizes closer to the originals without noticeably reducing image quality?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
5y ago
2 Answers
2
A difference between the settings used by GIMP and your digital camera likely explains the change in file sizes you're seeing. By default, GIMP appears to export JPEGs with quality 97 without subsampling. Many older digital cameras may use quality settings around 80-90 with subsampling. Using the first photo I encountered on my computer, saving with Q=90 + 4:2:2 subsampling resulted in a 3.9MB file. But saving with Q=97 + 4:4:4 subsampling resulted in a 14.1MB file. The change in file size is about 3.6x.
To maximize efficiency (lost data vs change in file size) when resaving JPEGs, it's usually preferable to use settings that are as close to the original as possible. GIMP has an option to facilitate this: Use quality settings from original image.
- For details, see What factors cause or prevent "generational loss" when JPEGs are recompressed multiple times?
When exporting to JPEG, there are several settings that affect file size. The primary settings to consider are in bold.
- Quality. Digital cameras usually use a setting similar to 94-98.
- Arithmetic coding. Don't enable this setting. Such files will not work with most image viewers or web browsers.
- Subsampling. Digital cameras usually use "4:2:2 horizontal (chroma halved)". Pick the option that halves the longer dimension.
- Optimize. This just optimizes some compression internals. Doesn't hurt to enable. Space savings are moderate.
- Progressive. Better to leave it off. Space savings are minimal, and files take longer to decode.
Originally by user75526. Source · Licensed CC BY-SA 4.0
user75526
5y ago
0
Generated from our catalog & community — verify before relying on it.
Mostly it’s GIMP’s JPEG export settings, with a smaller contribution from the edits themselves.
JPEG size depends heavily on compression settings: quality level and chroma subsampling. Older cameras often save JPEGs around roughly quality 80–90 with subsampling such as 4:2:2, while GIMP commonly exports at very high quality (around 97) and may use no subsampling (4:4:4). That alone can easily make files 3× larger.
Your edits can also increase file size a bit because stronger contrast/saturation can make an image less compressible.
To keep sizes closer to the originals, lower the JPEG quality setting somewhat and use subsampling. In GIMP, try the option to use the original image’s quality settings as a starting point, but be aware it may only estimate the camera’s original compression and may not match it exactly.
In short: the size jump is normal when re-exporting JPEGs at higher quality settings, and you can reduce it by choosing more moderate export settings with little or no visible quality loss.
Recommended products
UniqueBot
AI5y ago
Your Answer
Related Questions
Why can two similar JPEGs have very different file sizes?
Why are my camera JPEGs much larger than JPEGs exported by album software at the same resolution?
Why can two JPEGs from the same photo have different file sizes at the same resolution?
Why are some DNG files smaller than the original camera RAW files?
Why is a 16-bit TIFF much larger than the original RAW file?