Can Image Compression Reduce Quality?
Yes. Lossy compression can remove image information to reduce file size. The practical goal is to remove information that is difficult to notice rather than simply maximizing compression.
What to do
Use the least compression that meets your file-size requirement, and keep the original source file for future editing. The simplest next step is to Compress Image. If the issue is actually about jpg vs png, see JPG vs PNG as well.
Why this happens
Image problems often come from three separate variables: pixel dimensions, encoded file size and file format. Changing one does not automatically solve the others. A very large photo may need resizing even when its format is already JPG; a transparent graphic may need PNG or WebP even when the file size is acceptable; and an upload limit may be measured in megabytes rather than pixels.
Before editing, check the requirements of the place where the image will be used. That gives you a concrete target and reduces unnecessary quality loss. When possible, keep the original file and create a delivery copy for the specific destination.
Common questions
Is all compression lossy?
No. Lossless compression preserves the encoded image information, while lossy compression trades some information for smaller files.
Can PNG compression reduce quality?
Lossless PNG optimization can reduce file size without changing the image pixels, although the amount of reduction may be limited.
Should I compare at 100% zoom?
Check both normal viewing size and close-up areas where artifacts matter, such as text and fine textures.