，，PNGPDF
，、、，PNG；，、。，，， Sign PDF 。
From a phone photo to a usable signature
Ink on alpha, not ink on white
Signing a PDF with a raw photo leaves a white or yellowed rectangle floating over the document. This tool removes the paper entirely: it estimates the paper color from the photo's edges, then keys every pixel's transparency off how far its luminance and color sit from that background. The output is a transparent PNG where only the strokes remain.
Because the alpha ramp is continuous rather than a hard chroma-key cutoff, faint pen strokes keep partial opacity instead of snapping to fully-on or fully-off. That is what preserves the pressure texture of a real signature — the tapered start of a stroke stays tapered.
Tuned for real photos
Phone photos have shadows, wrinkles and uneven tint — the controls exist for them.
Ink color profiles
Auto-detect, blue ink, black ink, or red stamp — the extraction biases toward the hue you actually want.
Background cleaning
Bleaches white and yellowed paper, shadows, mold spots and wrinkles out of the alpha channel.
Edge contrast
Hardens stroke edges for a crisp stamp look, or softens them to keep faint pen pressure.
Straight into Sign PDF
One tap saves the PNG to your signature library and opens Sign PDF with it ready to place.
More than signatures
The same extraction works for corporate seals and hanko stamps (use the red profile), for line art you want to color digitally, and for any hand-drawn mark that needs to sit cleanly over another document. The result is trimmed to the ink's bounding box, so there is no dead transparent margin to fight when you place it.
Private by construction
The photo is decoded and processed on a local canvas — nothing is uploaded. A signature is biometric-adjacent personal data; it should never have to visit a server to be cleaned up.
，，PNGPDF: 常见问题解答
关于此工具及其工作原理的常见问题。
Pro
$29 一次性付费