What is the difference between the vintage, faded, and sepia presets?
Sepia is the raw sepia() filter, a straight tone map to brown. Vintage combines sepia at 60% with a slight saturation and contrast boost, which keeps some color while warming everything. Faded desaturates and lifts the blacks by lowering contrast and raising brightness, which is the washed-out film look, and it applies no sepia at all.
Can I stack two effects?
Not in one pass, since only one preset is active at a time. You can approximate it by downloading the result and feeding it back in as a new upload, though each round trip re-encodes the image. Several presets are already combinations internally: noir is grayscale plus contrast plus brightness, and warm tint is sepia plus hue-rotate plus saturate.
Why does the blur look weaker on a large photo?
Because blur is specified in absolute pixels. Six pixels of blur is a lot on a 400px thumbnail and almost invisible on a 4000px photo. If you need a heavy blur on a big image, resize it down first, or use a dedicated blur tool with a proportional radius.
Is a canvas blur enough to redact private information?
No, and this is important. A 6px blur is reversible in principle for text and faces, and the preset is designed as an aesthetic effect, not a redaction tool. To remove sensitive information from an image, paint over it with a solid block, then export. Never rely on a blur or a pixelation to hide something that matters.
Does the download keep my photo's EXIF data?
No. The image is drawn to a canvas and re-encoded as PNG, which keeps only pixels. Camera model, capture date, GPS coordinates, and the color profile are all discarded.
Why is the downloaded file so much bigger than my original?
Because the download is a PNG, which is lossless, and your source was probably a JPEG, which is not. If size matters, take the PNG and run it through the image converter at 90% WebP or JPEG quality.