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MaixCAM MaixPy Camera Usage
date author version content
2024-04-03
neucrack
1.0.0
Initial documentation

Introduction

For the MaixCAM, it comes with a pre-installed GC4653 camera, or an optional OS04A10 camera or global shutter camera, and even an HDMI to MIPI module, all of which can be directly used with simple API calls.

API Documentation

This article introduces common methods. For more API usage, refer to the documentation of the maix.camera module.

Camera Switching

Currently supported cameras:

  • GC4653: M12 universal lens, 1/3" sensor, clear image quality, 4MP.
  • OS04A10: M12 universal lens, 1/1.8" large sensor, ultra-clear image quality, 4MP.
  • OV2685: Does not support lens replacement, lowest image quality, and lowest cost; generally not recommended for use.
  • SC035HGS: Monochrome global shutter camera, 0.3MP black-and-white, suitable for capturing high-speed objects.

The system will automatically switch; simply replace the hardware to use.

Getting Images from the Camera

Using MaixPy to easily get images:

from maix import camera

cam = camera.Camera(640, 480)

while 1:
    img = cam.read()
    print(img)

Here we import the camera module from the maix module, then create a Camera object, specifying the width and height of the image. Then, in a loop, we continuously read the images. The default output is in RGB format. If you need BGR format or other formats, please refer to the API documentation.

from maix import camera, image
cam = camera.Camera(640, 480, image.Format.FMT_GRAYSCALE) # Set the output greyscale image

Also get the NV21 image

from maix import camera, image
cam = camera.Camera(640, 480, image.Format.FMT_YVU420SP) # set to output NV21 image

Note: You need to disable MaixVision's online browsing function if you set a very high resolution (e.g. 2560x1440), otherwise the code may run abnormally due to lack of memory. You can also get greyscale images

Setting the frame rate of the camera

Currently the camera supports 30fps, 60fps and 80fps configurations, the frame rate is selected by the width, height, fps parameters passed when creating the Camera object, currently the maximum supported resolution is 1280x720 under 60/80fps, and the maximum supported resolution is 2560x1440 under 30fps.

Setting the frame rate to 30 fps

from maix import camera
cam = camera.Camera(640, 480, fps=30) # set the frame rate to 30 fps
# or
cam = camera.Camera(1920, 1280) # Frame rate is set to 30 fps when resolution is higher than 1280x720

Set the frame rate to 60 fps

from maix import camera
cam = camera.Camera(640, 480, fps=60) # Set frame rate to 60 fps
# or
cam = camera.Camera(640, 480) # Set frame rate to 60fps if resolution is less than or equal to 1280x720

Set the frame rate to 80 fps

from maix import camera
cam = camera.Camera(640, 480, fps=80) # Set frame rate to 60 fps

Notes:

  1. if Camera is passed in a size larger than 1280x720, for example written as camera.Camera(1920, 1080, fps=60), then the fps parameter will be invalidated, and the frame rate will remain at 30fps.
  2. A 60/80fps frame will be offset by a few pixels compared to a 30fps frame, and the offset will need to be corrected if the viewing angle is critical.
  3. Note that due to the fact that 60/80fps and 30fps share the same isp configuration, in some environments there will be some deviation in the quality of the screen at the two frame rates.
  4. The camera's performance depends on the system. Some systems may not support setting the camera to 80fps, which can result in strange patterns appearing on the screen. In such cases, please switch back to the normal 60fps setting.

Image correction

In case of distortion such as fisheye, you can use the lens_corr function under the Image object to correct the distortion of the image. In general, you just need to increase or decrease the value of strength to adjust the image to the right effect.

``python from maix import camera, display

cam = camera.Camera(320, 240) disp = display.Display() while not app.need_exit():: t = time. t = time.ticks_ms() img = cam.read() img = img.lens_corr(strength=1.5) # Adjust the strength value until the image is no longer distorted. disp = display.Display() ``

Note that since the correction is done through software, it takes some time. Alternatively, you can use a distortion-free lens (inquire with the vendor) to solve the issue from a hardware perspective.

Skipping Initial Frames

During the brief initialization period of the camera, the image acquisition may not be stable, resulting in strange images. You can use the skip_frames function to skip the initial few frames:

cam = camera.Camera(640, 480)
cam.skip_frames(30)           # Skip the first 30 frames

Displaying Images

MaixPy provides the display module, which can conveniently display images:

from maix import camera, display

cam = camera.Camera(640, 480)
disp = display.Display()

while 1:
    img = cam.read()
    disp.show(img)

Setting the camera parameters

Set exposure time

Note that after setting the exposure time, the camera will switch to manual exposure mode, if you want to switch back to automatic exposure mode you need to run cam.exp_mode(0).

cam = camera.Camera()
cam.exposure(1000)

Setting the gain

Note that after setting the gain, the camera will switch to manual exposure mode, to switch back to auto exposure mode you need to run cam.exp_mode(0). Customised gain values will only work in manual exposure mode.

cam = camera.Camera()
cam.gain(100)

Setting the white balance

cam = camera.Camera()
cam.awb_mode(1)     # 0,turn on white balance;1,turn off white balance

Setting brightness, contrast and saturation

cam = camera.Camera()
cam.luma(50) # Set brightness, range [0, 100]
cam.constrast(50) # set contrast, range [0, 100]
cam.saturation(50) # Set the saturation, range [0, 100].

Using a USB Camera

In addition to using the MIPI interface camera that comes with the development board, you can also use an external USB camera. Method:

  • First, in the development board settings, select USB Mode under USB Settings and set it to HOST mode. If there is no screen available, you can use the examples/tools/maixcam_switch_usb_mode.py script to set it.
  • Currently (as of 2024.10.24), the maix.camera module does not yet support USB cameras, but you can use OpenCV for this.
from maix import image, display
import cv2
import sys

cap = cv2.VideoCapture(0)
cap.set(cv2.CAP_PROP_FRAME_WIDTH, 640)
cap.set(cv2.CAP_PROP_FRAME_HEIGHT, 480)
# cap.set(cv2.CAP_PROP_CONVERT_RGB, 0)

disp = display.Display()

if not cap.isOpened():
    print("Unable to open camera")
    sys.exit(1)
print("Starting to read")
while True:
    ret, frame = cap.read()
    if not ret:
        print("Unable to read frame")
        return
    img = image.cv2image(frame, bgr=True, copy=False)
    disp.show(img)