edgedetect.py

from kivy.clock import mainthread
from kivy.graphics import Color, Rectangle
from kivy.graphics.texture import Texture
import numpy as np
import cv2
from camera4kivy import Preview

class EdgeDetect(Preview):

    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self.analyzed_texture = None

    ####################################
    # Analyze a Frame - NOT on UI Thread
    ####################################

    def analyze_pixels_callback(self, pixels, image_size, image_pos, scale, mirror):
        # pixels : analyze pixels (bytes)
        # image_size   : analyze pixels size (w,h)
        # image_pos    : location of Texture in Preview (due to letterbox)
        # scale  : scale from Analysis resolution to Preview resolution
        # mirror : true if Preview is mirrored
        
        rgba   = np.fromstring(pixels, np.uint8).reshape(image_size[1],
                                                         image_size[0], 4)
        # Note, analyze_resolution changes the result. Because with a smaller
        # resolution the gradients are higher and more edges are detected.
        
        # ref https://likegeeks.com/python-image-processing/
        gray   = cv2.cvtColor(rgba, cv2.COLOR_RGBA2GRAY)
        blur   = cv2.GaussianBlur(gray, (3,3), 0)
        edges  = cv2.Canny(blur,50,100)
        rgba   = cv2.cvtColor(edges, cv2.COLOR_GRAY2RGBA) 
        pixels = rgba.tostring()

        self.make_thread_safe(pixels, image_size) 

    @mainthread
    def make_thread_safe(self, pixels, size):
        if not self.analyzed_texture or\
           self.analyzed_texture.size[0] != size[0] or\
           self.analyzed_texture.size[1] != size[1]:
            self.analyzed_texture = Texture.create(size=size, colorfmt='rgba')
            self.analyzed_texture.flip_vertical()
        if self.camera_connected:
            self.analyzed_texture.blit_buffer(pixels, colorfmt='rgba') 
        else:
            # Clear local state so no thread related ghosts on re-connect
            self.analyzed_texture = None
            
    ################################
    # Annotate Screen - on UI Thread
    ################################

    def canvas_instructions_callback(self, texture, tex_size, tex_pos):
        # texture : preview Texture
        # size    : preview Texture size (w,h)
        # pos     : location of Texture in Preview Widget (letterbox)
        # Add the analyzed image
        if self.analyzed_texture:
            Color(1,1,1,1)
            Rectangle(texture= self.analyzed_texture,
                      size = tex_size, pos = tex_pos)