Barcode Connector

Read and draw barcodes on MQTT

The Barcode connector turns an image on a topic into the text inside the symbol, or turns text into a PNG or PDF you can display and print. Point a camera connector at the decode event when the image is already a frame on MQTT.

Like a checkout scanner. You show it a picture of the code (decode), or you hand it the product number and it prints the label (encode).

When to use this

Use TYPE BARCODE when a camera, file, or upstream system already has the image, or when you need to generate a QR, retail, or 2D symbol from text. Limit SUPPORTED_FORMATS to the families you actually scan so detection stays fast.

Each tab below is a complete connector. Publish an image to the decode topic, or a JSON request to the encode topic.

Quick Start

Decode an image
Encode a symbol
Line scanner

Read a symbol from a base64 image and publish JSON, plus an annotated copy of the frame:

DEFINE ROUTE BarcodeScanner WITH TYPE BARCODE
    ADD BARCODE_CONFIG
        WITH SUPPORTED_FORMATS "QR_CODE,CODE_128,EAN_13,UPC_A"
    ADD EVENT ScanBarcode
        WITH MODE "DECODE"
        WITH SOURCE_TOPIC "camera/frame"
        WITH DESTINATION_TOPIC "barcode/decoded"
        WITH ANNOTATED_IMAGE_TOPIC "barcode/annotated"
        WITH ENABLE_ANNOTATION "true"
        WITH ANNOTATION_COLOR "Blue"
        WITH ANNOTATION_THICKNESS "3"

Generate a PNG from a JSON request on barcode/generate:

DEFINE ROUTE BarcodeGenerator WITH TYPE BARCODE
    ADD BARCODE_CONFIG
        WITH SUPPORTED_FORMATS "QR_CODE,CODE_128"
    ADD EVENT GenerateBarcode
        WITH MODE "ENCODE"
        WITH SOURCE_TOPIC "barcode/generate"
        WITH DESTINATION_TOPIC "barcode/image"

Decode two cameras on one connector, and annotate only the serial camera:

DEFINE ROUTE ProductionScanner WITH TYPE BARCODE
    ADD BARCODE_CONFIG
        WITH SUPPORTED_FORMATS "CODE_128,DATA_MATRIX"
    ADD EVENT ScanProduct
        WITH MODE "DECODE"
        WITH SOURCE_TOPIC "line/camera/frame"
        WITH DESTINATION_TOPIC "line/product/scanned"
    ADD EVENT ScanSerial
        WITH MODE "DECODE"
        WITH SOURCE_TOPIC "line/serial/frame"
        WITH DESTINATION_TOPIC "line/serial/decoded"
        WITH ENABLE_ANNOTATION "true"
        WITH ANNOTATED_IMAGE_TOPIC "line/serial/annotated"

Configuration

string

Comma-separated format names. Omit it to allow every format in the table below. Names are uppercase (QR_CODE, not qr_code).

Supported formats

Format	Kind
`QR_CODE`	2D
`CODE_128`	1D
`CODE_39`	1D
`EAN_13`	1D retail
`EAN_8`	1D retail
`UPC_A`	1D retail
`UPC_E`	1D retail
`PDF_417`	2D stacked
`DATA_MATRIX`	2D
`AZTEC`	2D
`ITF`	1D
`MSI`	1D
`PLESSEY`	1D
`CODABAR`	1D
`RSS_14`	1D
`RSS_EXPANDED`	1D
`MAXICODE`	2D

Events

Every event sets MODE to DECODE or ENCODE.

string

required

DECODE reads a symbol from an image. ENCODE draws a symbol from JSON.

string

required

Topic that triggers the event. Decode expects an image. Encode expects JSON.

string

required

Topic for the JSON result.

Decode

Publish the image as a raw base64 string. A data-URI prefix such as data:image/jpeg;base64, is accepted. A Video Input frame is already in that form, so you can set the decode SOURCE_TOPIC to the camera’s frame topic.

Annotation

string

true or false. Default: true. Draws a box around the symbol that was read.

string

Topic for the annotated image. The payload is a raw base64 string, same shape as the input image.

string

Color name, for example Red or Blue. Default: Red.

string

Line thickness as an integer. Default: 5.

A successful decode publishes JSON like this:

{
  "success": true,
  "text": "Decoded barcode text",
  "format": "QR_CODE",
  "timestamp": "2024-01-01T12:00:00.000Z",
  "route_name": "BarcodeScanner",
  "event_name": "ScanBarcode"
}

When no symbol is found, success is false and error explains why (for example No barcode found in image). Check success before you trust text. Large frames are scaled down before detection. If a sharp 1080p frame still fails, publish a 1280×720 or 640×480 image instead.

Encode

Publish JSON on the encode SOURCE_TOPIC. text is the payload to draw. format must be one of the names in SUPPORTED_FORMATS.

{
  "text": "Product-12345",
  "format": "QR_CODE",
  "width": 300,
  "height": 300,
  "margin": 0,
  "output_type": "IMAGE"
}

Field	Default	Role
`text`	—	Content to encode
`format`	—	Symbol family, uppercase
`width` / `height`	—	Pixel size of the symbol
`margin`	`0`	Quiet zone around the symbol
`output_type`	`IMAGE`	`IMAGE` (PNG data-URI) or `PDF`

An image result includes image_base64 (data:image/png;base64,…). A PDF result includes pdf_base64 (data:application/pdf;base64,…). Both include success, text, format, output_type, width, height, timestamp, route_name, and event_name.

PDF page placement

Set output_type to PDF and add pdf_options. Units are points (A4 is 595 × 842).

Field	Default	Role
`page_width`	`595`	Page width
`page_height`	`842`	Page height
`x_position`	`50`	Left edge of the symbol
`y_position`	`750`	Baseline position on the page
`include_text`	`true`	Print the encoded text on the page
`text_below`	`true`	Place that text under the symbol
`font_size`	`12`	Text size

{
  "text": "1234567890123",
  "format": "EAN_13",
  "width": 300,
  "height": 100,
  "output_type": "PDF",
  "pdf_options": {
    "page_width": 595,
    "page_height": 842,
    "x_position": 50,
    "y_position": 750,
    "include_text": true,
    "text_below": true,
    "font_size": 12
  }
}

Trigger from an action

Publish the image or the encode JSON straight to SOURCE_TOPIC, or hand the payload to a named event:

DEFINE ACTION DecodeBarcodeFromImage
ON TOPIC "camera/capture" DO
    TRIGGER "BarcodeScanner" TO PAYLOAD FOR "ScanBarcode"

DEFINE ACTION GenerateQRCode
ON TOPIC "qr/generate" DO
    SET "data" WITH CLEAN:{text: {value.json.text}, format: "QR_CODE", width: 300, height: 300, output_type: "IMAGE"}
    TRIGGER "BarcodeGenerator" TO {data} FOR "GenerateBarcode"

Best Practices

Image quality

Use a sharp, evenly lit frame. Blur and glare are the usual reason decode returns No barcode found in image. For retail codes, 640×480 to 1280×720 is enough.

Format selection

QR for URLs and mixed content. EAN-13 and UPC-A for retail. Code 128 for alphanumeric IDs. List only those names in SUPPORTED_FORMATS.

Errors

Branch on success. A false result still arrives on DESTINATION_TOPIC, so a downstream action should not treat every message as a good scan.

Troubleshooting

No barcode found in image

Confirm the symbol is in frame and the format name is listed in SUPPORTED_FORMATS. Retry with a smaller, sharper image.

Invalid barcode format

Use the uppercase names from the format table, spelled exactly, and include that name in SUPPORTED_FORMATS.

Base64 decode error

The payload must be the base64 image, with or without a data:image/…;base64, prefix, and with no extra characters around it.

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Product Updates

Read and draw barcodes on MQTT

When to use this

Quick Start

Configuration

Supported formats

Events

Decode

Encode

Trigger from an action

Best Practices

Troubleshooting

Next Steps

Video Input

Media Connectors

​Read and draw barcodes on MQTT

​When to use this

​Quick Start

​Configuration

​Supported formats

​Events

​Decode

​Encode

​Trigger from an action

​Best Practices

​Troubleshooting

​Next Steps

Video Input

Media Connectors

Read and draw barcodes on MQTT

When to use this

Quick Start

Configuration

Supported formats

Events

Decode

Encode

Trigger from an action

Best Practices

Troubleshooting

Next Steps