About

Scanned signatures carry noise: paper grain, uneven lighting, colored ink that photocopies poorly. When embedded into contracts or official documents, these artifacts reduce legibility and appear unprofessional. This converter isolates signature strokes from background using luminosity-based thresholding - pixels darker than a configurable boundary become pure black (0,0,0), while lighter pixels convert to transparent alpha. The algorithm applies ITU-R BT.601 grayscale weighting: 0.299R + 0.587G + 0.114B, matching human brightness perception. Output PNG files embed correctly over any document background without white rectangles or color fringing.

Threshold calibration matters. Set too low, faint strokes vanish. Set too high, paper texture bleeds through. The real-time preview lets you find the boundary where ink separates cleanly from substrate. For signatures on lined paper or colored stock, increase contrast preprocessing to push the histogram apart before thresholding. Note: This tool processes locally in your browser - no signature data leaves your device.

Formulas

The conversion pipeline applies two sequential transforms to each pixel.

L = 0.299R + 0.587G + 0.114B

where L is the luminosity (perceived brightness), and R, G, B are the red, green, blue channel values ranging 0 - 255. Contrast enhancement is applied before thresholding.

L′ = (L − 128) × C + 128

where C is the contrast multiplier (1.0 = no change). The thresholding decision follows.

{

A = 0, R=G=B=0 if L′ < TA = 255 (opaque black ink) otherwise transparent

where T is the user-set threshold, and A is the alpha channel. Pixels below threshold become solid black; pixels at or above become fully transparent.

Reference Data

Parameter	Recommended Range	Effect
Threshold	100 - 180	Cutoff luminosity; lower keeps more detail
Contrast	1.0 - 2.5	Pre-processing histogram stretch
White Paper Scan	Threshold 140 - 160	Clean separation typical
Yellow/Cream Paper	Threshold 120 - 140	Compensates for warm base
Blue Ink Original	Threshold 110 - 130	Blue is darker in luminosity
Pencil Signature	Threshold 90 - 120, Contrast 2.0+	Faint strokes need boost
Red Ink Original	Threshold 130 - 150	Red luminosity similar to paper
Photo of Signature	Contrast 1.8+, Threshold 120 - 150	Uneven lighting needs contrast
Output Format PNG	Transparency supported	Best for documents, web
Output Format JPEG	White background fallback	Smaller file, no transparency
DPI for Print	300 DPI minimum	Scan at high res for quality
Recommended Input Size	1000 - 3000px width	Balance detail vs. processing
Max Supported Size	8000 × 8000px	Browser memory limits
File Size Limit	10 MB	Prevents browser freeze
Grayscale Weight R	0.299	ITU-R BT.601 standard
Grayscale Weight G	0.587	Human eye most sensitive
Grayscale Weight B	0.114	Least perceptual weight

Frequently Asked Questions

Thin strokes have luminosity values close to the paper background. Lower the threshold value by increments of 5 - 10 until strokes appear. Alternatively, increase contrast to 1.5 - 2.0 which pushes ink pixels darker before thresholding, preserving fine details.

Paper grain and dust create low-luminosity noise. Raise the threshold until speckles disappear. If signature strokes also fade, increase contrast preprocessing - this stretches the histogram so paper noise stays above threshold while ink drops below.

Yes. The algorithm uses luminosity, not hue. Blue ink typically has luminosity around 80 - 130, red ink 100 - 150. Adjust threshold to fall between ink luminosity and paper luminosity (usually 200+ for white paper). All ink colors become black (0,0,0) in output.

For print documents, scan at minimum 300 DPI. A signature 2 inches wide at 300 DPI yields 600px width - sufficient for most contracts. Higher resolutions (600 DPI) preserve fine strokes but increase processing time. Phone photos at 12 MP are typically adequate.

Microsoft Word sometimes flattens PNG transparency on insertion. Right-click the image, select Format Picture, and ensure no fill is applied. Alternatively, use Insert Picture rather than copy-paste. LibreOffice and Google Docs preserve transparency correctly by default.

No. All processing occurs locally in your browser using the Canvas API. The signature image never leaves your device. You can verify by disconnecting from the internet - the tool functions identically offline.