DX Film Edge Barcode

The DX film edge barcode is Kodak's latent-image code printed along the edge of 35mm film below the sprocket holes, invisible until developed. It identifies the film's manufacturer/type ("DX number"), generation and, every half frame, the frame number — used by photofinishing equipment to process and print film automatically. It is a two-track code: a fixed "clock" track for scanner synchronization, and a "data" track carrying the actual bits.

This is distinct from the DX cartridge barcode (an ordinary Interleaved 2 of 5 symbol printed on the film cartridge, already coverable by this SDK's existing itf format) and from the DX CAS conductive checkerboard pattern read electrically by camera contacts — neither of those is what this format implements.

Structure

Field	Bits	Notes
Start pattern	6	Fixed 101010
Product code	7	1-127
Separator	1	Fixed 0
Generation	4	0-15; product code + generation together form the DX number
Frame number (optional)	6	0-63, half-frame intervals
Half-frame flag (optional)	1	Set for the second half of a frame pair
Separator (optional)	1	Fixed 0
Parity	1	XOR of every data-track bit between the start and stop patterns
Stop pattern	4	Fixed 0101

A symbol without frame information is 23 bits wide; with frame information, 31 bits. The clock track runs in parallel (row 0 of the rendered matrix, data track row 1) with its own fixed synchronization pattern determined purely by the symbol's length — it carries no user data.

Runtime id dxfilmedge, reported by listFormats() as writable and readable like any other 1D format.

Writing

import { encodeDXFilmEdge } from '@sythos/js_barcode_universal/oned';

// Product code + generation only (no frame info)
const noFrame = encodeDXFilmEdge({ productCode: 79, generation: 7 });

// With frame number and half-frame flag
const withFrame = encodeDXFilmEdge({
  productCode: 79,
  generation: 7,
  frameNumber: 23,
  halfFrame: true,
});

The root dispatcher accepts the same field object as value:

import { encode, toImageData } from '@sythos/js_barcode_universal';

const matrix = encode({ productCode: 79, generation: 7 }, { format: 'dxfilmedge' });
const image = toImageData(matrix, { scale: 5, margin: 16 });

Reading images

import { decode, toImageData } from '@sythos/js_barcode_universal';

const image = toImageData(
  encode({ productCode: 79, generation: 7, frameNumber: 23, halfFrame: true }, { format: 'dxfilmedge' }),
  { scale: 5, margin: 16 },
);

const [result] = decode(image, { formats: ['dxfilmedge'] });
console.log(result?.productCode, result?.generation, result?.frameNumber, result?.halfFrame);
// 79 7 23 true

The reader validates the fixed clock-track pattern, the start/stop patterns and the parity bit before returning a result; any mismatch returns nothing rather than a guessed value. For camera capture, opt into the stricter profile:

const hits = decode(cameraFrame, { formats: ['dxfilmedge'], profile: 'camera' });

The camera profile requires a measurable quiet zone on both sides of the symbol, the same requirement as this SDK's other height/track-coded formats.

Verification and licensing boundary

The bit-field layout, fixed clock-track patterns and parity algorithm are original Sythos code, verified against US Patent 4,965,628A's own page images (not automated text extraction, which — like this SDK's PostBar implementation — was found to produce a conflicting result compared to the primary source) and cross-checked against Wikipedia's "DX encoding" article (itself citing a 2017 peer-reviewed archival-science paper analyzing real film samples) and Zint's dxfilmedge.c, consulted only as an independent black-box behavioural reference. No source code, table or image asset from any other barcode implementation is copied or shipped. See licenses/dx-film-edge-barcode.license and NOTICE.md. This implementation is not certified, endorsed or reviewed by Kodak.