
Compressing images without visible loss
What a quality setting really controls, what chroma subsampling throws away, which SSIMULACRA 2 scores map to which settings, and why re-encoding hurts.

Erasing a corner badge is a reconstruction, not a recovery. And when the visible mark goes, the provenance record and the embedded signal inside the file stay exactly where they were.
"Remove the watermark" covers three unrelated jobs, and which one applies depends entirely on where the badge sits.
Whichever you pick, the file you end up with is not the original restored. The real pixels underneath the logo were never present in the file you hold. Inpainting does not recover them; it manufactures something plausible in their place.
You supply a mask: a black and white image marking which pixels to discard. The algorithm starts at the boundary of that region and works inwards, carrying colour and structure from the edge into the hole. The quality of the result is therefore decided by what surrounds the mask, not by what was inside it. Flat sky, a blurred background or a solid panel produce near perfect results, because the information read from the edge remains true further in.
The Gemini logo remover runs this on the server rather than in the browser. Once the image is uploaded there are two paths. In automatic mode the server first trims uniform black or white letterbox bands so the corners map onto the real photo, then searches a corner quadrant for a four-pointed sparkle shape at six different scales, weighting the bottom corners more heavily. If the shape match is not confident it falls back to picking the most compact blob that stands out from the corner's background colour, and if that fails too it cleans a modest corner square roughly a sixth of the short edge. In manual mode you brush over the logo yourself; the browser scales that selection up to the image's native resolution, turns it into a black and white mask and sends it alongside the file.
Reconstruction then runs on a small box cropped around the mask. Frequency selective reconstruction is used where it is available, with Telea or Navier-Stokes as the fallback. The mask is grown by a few pixels on purpose, because a logo's soft edge and the faint halo around it leave a visible ghost if they fall outside the selection. PNG, JPG and WebP are accepted up to 25 MB, and the temporary files are deleted once the job finishes.
You can predict how cleanly a logo will lift before you try.
| Situation | Expected result |
|---|---|
| Small opaque logo on a flat corner | Undetectable |
| Logo over a blurred background | Undetectable |
| Logo over a textured surface | A soft patch, visible up close |
| Semi-transparent mark across half the frame | Poor; the detail underneath does not come back |
| Logo sitting on a face, lettering or a straight edge | Poor; the algorithm invents something plausible and wrong |
The reasoning is consistent. Inpainting extends structure inwards from the boundary. When a real object genuinely continues under the mask, such as an eye, a letterform or a window frame, the algorithm has no knowledge of it and simply continues what it can see around the edge. What comes out looks reasonable and bears no relationship to what was there. Semi-transparent watermarks are the worst case, because the region to rebuild is not a small blob but a large share of the picture.
This is the part almost every article on the subject leaves out. The corner badge is not the only thing marking an image as generated. A file can carry up to three further layers that you cannot see, and erasing the badge removes none of them.
C2PA embeds a signed provenance record, called a manifest, inside the file. The specification defines two kinds of binding: a hard binding built from cryptographic hashes, and a soft binding built from a fingerprint or an invisible watermark. Editing pixels breaks the hard binding, but that is not a win for anyone trying to hide an edit: validation then reports that the asset has been tampered with, so the change is detected rather than erased. The soft binding is designed to survive editing outright. The specification itself gives the example of an asset separated from its manifest by metadata removal, where a fingerprint of the content is used to look the intact manifest back up from a database.
Google's SynthID writes its mark into the pixels themselves. DeepMind describes the watermark as imperceptible to humans and designed to stand up to modifications like cropping, adding filters, changing frame rates or lossy compression. The Gemini API documentation puts the scope in one line: all generated images include a SynthID watermark. Painting out the sparkle in the corner removes the visible badge and leaves that signal in place, and Google can check an uploaded image against it.
The third layer is ordinary metadata. Software fields inside EXIF can name the program that wrote the file, and the IPTC digital source type field exists specifically to state how an image was produced. Those extension fields live only in XMP, not in EXIF. The EXIF remover is useful here but bounded: it runs in the browser and targets the EXIF blocks in JPEG files, either stripping them entirely or keeping the categories you choose. It does not touch XMP packets or the container that holds a C2PA manifest. Output from the logo remover is re-encoded by the imaging library, so it carries no embedded metadata to begin with, which clears EXIF and does nothing to a mark living in the pixels.
The one-line version: taking off the badge changes how the image looks, not what it is. It does not make an AI image undetectable, and it does not make it unattributable.
The legitimate case is clear enough. Images you generated yourself, where a corner badge simply clutters your own slide, product page or cover layout, and removing it is a design decision like any other.
Three situations are genuinely problematic, and none of them is a technical question.
The same steps in a different sequence give a different result.
Very likely, yes. Embedded marks such as SynthID are written into the pixels and designed to survive cropping, filters and lossy compression. C2PA additionally allows a provenance manifest to be looked up again from a fingerprint of the content. Removing the visible badge only changes the appearance.
Inpainting extends the colour and structure found at the mask boundary inwards. Where the surroundings are flat or blurred the repair is invisible. Where there is strong texture, lettering or an object that genuinely continues underneath, the algorithm cannot know that and produces something plausible but wrong. The larger the mask, the more obvious the error.
If the logo is in a corner and you can afford to lose that strip, cropping is always better: nothing is guessed, it is only discarded. Inpainting earns its place when the badge sits inside the frame or the aspect ratio has to stay as it is.
No. The EXIF remover runs in the browser and targets EXIF blocks in JPEG files. It does not touch XMP packets or the container holding a C2PA manifest. The logo remover's output is re-encoded, so it carries no embedded metadata at all, but that has no effect on a mark stored in the pixels.
Yes. A watermark is usually a licensing and ownership signal, removing it grants no right to use the work, and many jurisdictions treat stripping rights-management information as a separate violation. The legitimate use of this kind of tool is your own generated images, where the badge interferes with your own layout.

What a quality setting really controls, what chroma subsampling throws away, which SSIMULACRA 2 scores map to which settings, and why re-encoding hurts.

Measured compression figures with sources, WebP's 8-bit and 4:2:0 ceilings, AVIF's encode cost and missing progressive rendering, and how to choose per content type.