Compress Images in DeDup 1.5.3 on Android: WebP output and what happens to originals

Compress Images in DeDup 1.5.3 re-saves your larger JPEG and PNG photos as lossy WebP files at a quality you choose. By default it then deletes the original, without the system confirmation that the scanners use. Read the options before you tap the button.

Where it is and what it lists

Open the Optimize tab and choose "Compress Images". The screen lists JPEG and PNG photos larger than 500 KB, biggest first, with a count at the top. The code uses 500 x 1,024 bytes as the cutoff. Every photo starts ticked. "Select All" and "Deselect All" are in the top bar. If nothing qualifies, the screen says all images are already optimized.

The choices

• Quality slider. It runs from 50 to 95 in whole-number steps and starts at 85. A label next to it changes with the value: "Lossless-ish" at 90 and above, then "Excellent", "Good", "Fair" and "Low".
• Delete originals. A switch, on by default.
• Which photos. Tick or untick each row.

The estimates on screen, both per photo and the "Est. savings" line at the bottom, come from fixed formulas in the code. They aren't measured, and the two use different formulas, so they won't agree. The card also carries a line about average size reduction, and nothing in the code measures that. The card under the Optimize tab says "without losing quality", but the output is lossy WebP at every slider position, so that wording isn't accurate.

What it produces

For each selected photo, one at a time, DeDup decodes it and re-encodes it as WebP at your quality setting. Photos with a long side of 7,000 pixels or more are decoded at half size or smaller, so the new file has fewer pixels. JPEGs are decoded at a lower colour depth (RGB_565). I found no code that copies the original's metadata to the new file.

The result is added to your photo library as a new image named like the original with "_dedup_q" and the quality added, ending in .webp. A file called beach.jpg at quality 85 becomes beach_dedup_q85.webp. The code doesn't pass a folder, so I can't say where Android puts it. A photo that fails to decode or save is skipped, with no message.

What happens to the original

If "Delete originals" is on, DeDup asks Android to delete the original as soon as the new file is saved. This path doesn't use the system delete prompt that the scanners use. If Android refuses, DeDup writes a log entry and carries on. It doesn't tell you, so you could end up with both files. The code doesn't compare the two sizes before it deletes, and the delete isn't sent to DeDup's Trash.

If the switch is off, the original stays.

What you see afterwards

During the run you see "Compressing… done / total" and a running "Saved ... so far" figure. Afterwards a summary reads "N images compressed", with the amount saved, and the list reloads. The saved figure is the original size minus the new size, calculated whether or not the original was removed. With the switch off, nothing is freed. I found no Stop button on this screen.

Scope of this post

Checked against: DeDup 1.5.3 source code (Android).

Not tested on a device: whether Android allows the direct delete of an original for a given photo or Android version, where the new files appear, how the images look at each quality, or how big the real savings are. I read the code for each of these but didn't run it.