Images compression is easiest when you stop treating “quality” as one number. A setting that looks excellent on a soft landscape can make a screenshot unreadable. The right target depends on what the image contains and where it will be used.
Resize before you squeeze quality too hard
If a 4000-pixel-wide photo will only ever appear at 1200 pixels, reducing the dimensions often saves more space than aggressively lowering JPEG quality. You are removing pixels the final display does not need instead of asking the encoder to destroy more detail inside an oversized image.
Judge the difficult parts of the image
Do not inspect only the center. Zoom in on text, hair, product edges, fine patterns and smooth gradients. Compression artifacts usually become visible there first. For a screenshot, check small labels. For a portrait, check eyes and hair. For a product image, check sharp edges against plain backgrounds.
Use the destination to set the target
An email attachment, ecommerce thumbnail and portfolio image do not need the same settings. If an upload form has a hard file-size limit, optimize to stay comfortably below it. For a website, balance transfer size with how prominent the image is. A tiny decorative thumbnail can tolerate more compression than a full-width hero image.
Avoid repeated lossy exports
Lossy compression is cumulative. If possible, start from the best available source and create the delivery copy once. Editing yesterday’s compressed JPG and saving it again today can introduce additional artifacts even if you choose the same nominal quality setting.
Keep a master copy
The compressed file is a delivery copy, not a replacement for your original. Store the high-quality source separately. This matters if you later need a larger crop, a print version or a new format.
Transparency and screenshots need special care
For graphics with transparency, avoid converting to JPEG unless a solid background is acceptable. For screenshots containing lots of flat color and sharp text, PNG can sometimes be both clearer and more efficient than a heavily compressed JPEG.
A practical compression routine
- Make a copy of the original.
- Resize to the largest dimensions you genuinely need.
- Export at a moderate quality setting.
- Compare the result at 100% zoom.
- Lower quality gradually only if the file is still too large.
- Open the final file once more before publishing or sending it.
The goal is not the smallest possible file. The goal is the smallest file that still does its job.