Opacity describes how much of an image is visible when it is placed over a background. Changing opacity can help create an overlay, but the saved format must preserve alpha for that effect to travel with the file.
Image Opacity returns PNG with reduced opacity. It scales the visibility already present in the source rather than making every pixel equally opaque first.
Read the percentage as visibility
An opaque pixel at 100% remains opaque. At 0%, it becomes fully transparent. An already partly transparent pixel at 50% becomes less visible again; the operation does not restore its missing opacity.
The canvas width and height stay unchanged. The checker background in the preview shows the transparent areas and is not part of the download.
A fully transparent result can appear empty even though it is a valid PNG with the original dimensions. Check the percentage before assuming the upload failed.
Judge it over the intended background
A logo at reduced opacity can look subtle on white and much stronger on a dark surface. The final appearance depends on both the saved alpha and the background beneath it.
Converting the PNG to JPEG later flattens the image onto a solid colour. That loses the reusable opacity behaviour, so retain the PNG for overlays.
This tool applies one visibility percentage to the whole image. It does not create a selective mask around a subject or change only the background.
When making a watermark, you may prefer the logo overlay tool because it also places a second image onto a base. Use this opacity operation when you want a standalone transparent asset that another editor or webpage will composite later.