MaixCAM MaixPy QR Code Recognition

2024-04-03

Update history

Date	Version	Author	Update content
2024-04-03	1.0.0	lxowalle	Initial document

Before reading this article, make sure you are familiar with how to develop with MaixCAM. For details, please read Quick Start.

Introduction

This article explains how to use MaixPy for QR code recognition.

Using MaixPy to Recognize QR Codes

MaixPy's maix.image.Image includes the find_qrcodes method for QR code recognition.

How to Recognize QR Codes

A simple example that recognizes QR codes and draws a bounding box:

from maix import image, camera, display

cam = camera.Camera(320, 240)
disp = display.Display()

while True:
    img = cam.read()
    qrcodes = img.find_qrcodes()
    for qr in qrcodes:
        corners = qr.corners()
        for i in range(4):
            img.draw_line(corners[i][0], corners[i][1], corners[(i + 1) % 4][0], corners[(i + 1) % 4][1], image.COLOR_RED)
        img.draw_string(qr.x(), qr.y() - 15, qr.payload(), image.COLOR_RED)
    disp.show(img)

Steps:

Import the image, camera, and display modules:
```
from maix import image, camera, display
```

Initialize the camera and display:

cam = camera.Camera(320, 240)  # Initialize the camera with a resolution of 320x240 in RGB format
disp = display.Display()

Capture and display images from the camera:

while True:
    img = cam.read()
    disp.show(img)

Use the find_qrcodes method to detect QR codes in the camera image:
```
qrcodes = img.find_qrcodes()
```
- img is the camera image captured by cam.read(). When initialized as cam = camera.Camera(320, 240), the img object is a 320x240 resolution RGB image.
- img.find_qrcodes searches for QR codes and saves the results in qrcodes for further processing.
Process and display the results of QR code recognition on the screen:
```
for qr in qrcodes:
    corners = qr.corners()
    for i in range(4):
        img.draw_line(corners[i][0], corners[i][1], corners[(i + 1) % 4][0], corners[(i + 1) % 4][1], image.COLOR_RED)
    img.draw_string(qr.x(), qr.y() - 15, qr.payload(), image.COLOR_RED)
```
- qrcodes contains the results from img.find_qrcodes(). If no QR codes are found, qrcodes will be empty.
- qr.corners() retrieves the coordinates of the four corners of the detected QR code. img.draw_line() uses these coordinates to draw the QR code outline.
- img.draw_string displays information about the QR code content and position. qr.x() and qr.y() retrieve the x and y coordinates of the QR code's top-left corner, and qr.payload() retrieves the content of the QR code.

Common Parameter Explanation

List common parameters and their explanations. If you cannot find parameters that fit your application, consider whether to use a different algorithm or extend the functionality based on the current algorithm's results.

Parameter	Description	Example
roi	Sets the rectangular area for the algorithm to compute, where roi=[x, y, w, h], x and y denote the top-left coordinates of the rectangle, and w and h denote the width and height of the rectangle, defaulting to the entire image.	Compute the area with coordinates (50,50) and width and height of 100: `img.find_qrcodes(roi=[50, 50, 100, 100])`
qrcoder_type	Set the QR code library decoder type; you can choose either `image.QRCodeDecoderType.QRCODE_DECODER_TYPE_ZBAR` or `image::QRCodeDecoderType::QRCODE_DECODER_TYPE_QUIRC`. `QRCODE_DECODER_TYPE_ZBAR` offers faster recognition speed and higher accuracy at lower resolutions. `QRCODE_DECODER_TYPE_QUIRC` is relatively faster at higher resolutions but with slightly lower accuracy. By default, `QRCODE_DECODER_TYPE_ZBAR` is used. Effective in version 4.7.7 and later.	img.find_qrcodes(decoder_type=image.QRCodeDecoderType.QRCODE_DECODER_TYPE_ZBAR)

This article introduces common methods. For more API details, refer to the image section of the API documentation.

Using Hardware Acceleration for QR Code Detection

MaixPy includes a built-in image.QRCodeDetector object that can use hardware acceleration for QR code detection. At a resolution of 320x224, the maximum frame rate for a single-frame algorithm can reach 60+ fps.

Note: This feature is supported in MaixPy v4.7.9 and later versions

Usage

from maix import camera, display, app, image

cam = camera.Camera(320, 224)
disp = display.Display()
detector = image.QRCodeDetector()

while not app.need_exit():
    img = cam.read()

    qrcodes = detector.detect(img)
    for q in qrcodes:
        img.draw_string(0, 0, "payload: " + q.payload(), image.COLOR_BLUE)

    disp.show(img)

Steps:

Import the image, camera, and display modules:

from maix import camera, display, app, image

Capture and display the image:
```
cam = camera.Camera(320, 224)
disp = display.Display()

while not app.need_exit():
    img = cam.read()
    disp.show(img)
```
- Create Camera and Display objects. Use the cam.read() method to capture the image and the disp.show() method to display it.
Create a QRCodeDetector object for QR code detection:
```
detector = image.QRCodeDetector()
```
Use the detect method to detect QR codes, saving the results in the qrcodes variable:
```
qrcodes = detector.detect(img)
for q in qrcodes:
    img.draw_string(0, 0, "payload: " + q.payload(), image.COLOR_BLUE)
```
- Note: The detection process will utilize NPU resources. If other models are using the NPU at the same time, it may cause unexpected results.
- The structure of the detection result is the same as the data returned by find_qrcodes. Refer to the QRCode object's methods to access the detection results. For example, calling q.payload() will retrieve the QR code's content string.

Line tracking

Barcode identity