About

Adding text labels to images is a routine task in documentation, social media content preparation, and asset management. Incorrect label placement or poor contrast against the background can render text illegible, especially after compression or resizing. This tool composites text directly onto the pixel buffer via the Canvas API, producing a flattened raster output. You control font family, size (s in px), fill color, background color with opacity (α from 0 to 1), padding, and exact position via drag-and-drop. The output respects the original image resolution. Note: this tool does not embed metadata or vector layers. The label is burned into the bitmap. For reversible annotations, a vector format (SVG) would be required.

Formulas

The label bounding box on canvas is calculated from text metrics. The rendered width W of a text string is obtained via the Canvas measureText method. Total label dimensions including padding p:

W_label = W_text + 2p

H_label = n × s × l + 2p

where n = number of text lines, s = font size in px, l = line-height multiplier (default 1.3), and p = padding in px. The background rectangle uses the RGBA color model with alpha α controlling transparency:

rgba(R, G, B, α) - α ∈ [0, 1]

Canvas coordinates map the label position (x, y) from display space to full-resolution image space using the scale factor k:

k = W_imageW_canvas

x_real = x_display × k

Reference Data

Font Family	Category	Best Use Case	Legibility at Small Sizes
Arial	Sans-serif	General purpose, UI labels	Excellent
Helvetica	Sans-serif	Clean design, professional	Excellent
Georgia	Serif	Editorial, formal captions	Good
Times New Roman	Serif	Academic, traditional	Fair
Courier New	Monospace	Code labels, technical	Good
Verdana	Sans-serif	Screen readability	Excellent
Trebuchet MS	Sans-serif	Web content, headings	Good
Impact	Sans-serif	Bold headlines, memes	Poor (condensed)
Comic Sans MS	Casual	Informal, children’s content	Good
Palatino	Serif	Book typography	Good
Garamond	Serif	Print, elegant documents	Fair at < 10px
Tahoma	Sans-serif	Compact UI, small labels	Excellent
Lucida Console	Monospace	Technical overlays	Good
Brush Script MT	Script	Decorative, watermarks	Poor
Segoe UI	Sans-serif	Modern Windows UI	Excellent

Frequently Asked Questions

No. The export canvas is sized to the original image dimensions. The label is composited at full resolution using the scale factor k to map display coordinates to pixel coordinates. The output file matches the source resolution exactly.

Setting α below 0.5 on a complex background significantly reduces contrast ratio, potentially failing WCAG AA requirements (4.5:1 for normal text). For photographs with varied luminance, use α ≥ 0.7 or add a text stroke (outline) for guaranteed legibility.

The preview canvas is scaled to fit your screen, while the export renders at the original image size. Font rendering may differ slightly because the export uses a proportionally larger font size (s × k). Anti-aliasing behavior also varies by browser and OS. The spatial layout and proportions remain identical.

This tool is designed for a single label operation. For multiple labels, download the result and re-upload it for the next label. Each pass flattens the previous label into the raster, so the process is non-destructive to quality (PNG) but cumulative on JPEG due to recompression.

Canvas elements have browser-imposed limits (typically 16384 × 16384 px on desktop, lower on mobile). If the image exceeds your browser's maximum canvas area, the export may produce a blank or corrupted file. Images under 4096 × 4096 px work reliably across all platforms.

Yes. JPEG uses lossy DCT compression that creates ringing artifacts around sharp edges, including text. At quality 0.92 or above, artifacts are minimal. For crisp text labels, PNG is the recommended format. Use JPEG only when file size is a constraint.