modern-pdf-lib

---

modern-pdf-lib / estimateJpegQuality

Function: estimateJpegQuality()

estimateJpegQuality(jpegBytes): number | undefined

Defined in: src/assets/image/imageOptimize.ts:350

Estimate the JPEG quality level (1–100) from the quantization tables embedded in a JPEG file.

Parses the DQT (Define Quantization Table, marker 0xFFDB) segments from the raw JPEG bytes and compares the table values against the standard JPEG luminance quantization table to estimate the quality factor that was used during encoding.

If no DQT marker is found, returns undefined.

Parameters

jpegBytes

Uint8Array

Raw JPEG file bytes.

Returns

number | undefined

Estimated quality 1–100, or undefined if no DQT is found.

Example

import { estimateJpegQuality } from 'modern-pdf-lib';

const quality = estimateJpegQuality(jpegBytes);
if (quality !== undefined) {
  console.log(`Estimated JPEG quality: ${quality}`);
}