python-pillow/Pillow

from PIL import Image

colors = ((0,160,0),(33,150,243),(88,88,88),(255,0,0))

with Image.open('tradingview.png') as im:
    px = im.load()
    x, y = 0, 0
    currentColor = None
    processedPixels = []
    i = 0

    # Start searching through all the pixels
    for y in range(0, im.height):
        for x in range(0, im.width + 1):
            def getColor(x, y):
                try:
                    return px[x, y]
                except IndexError:
                    return

            if (x, y) in processedPixels:
                continue
            color = getColor(x, y)
            if color != currentColor:
                if currentColor is not None:
                    max_x = x

                    # The color line has ended, from min_x to max_x
                    x_range = min_x, max_x

                    # The left side of our rectangle must also be a solid color
                    # So search from the top left until we have a solid left side
                    for y2 in range(y+1, im.height+1):
                        for x2 in range(min_x, max_x+1):
                            if getColor(x2, y2) == currentColor:
                                min_x = x2
                                break
                        else:
                            # No color in this line, so we have hit the bottom of the rectangle
                            max_y = y2
                            break

                    # The same for the right side
                    for y2 in range(y+1, max_y+1):
                        for x2 in range(max_x+1, min_x, -1):
                            if getColor(x2, y2) == currentColor:
                                max_x = x2
                                break

                    # Check that this rectangle is of a reasonable size
                    if max_x - min_x > 10 and max_y - y > 10:
                        # Record that we've processed these pixels, to save time
                        for y2 in range(y, max_y+1):
                            for x2 in range(x_range[0], x_range[1]+1):
                                processedPixels.append((x2, y2))

                        # Check that the box is not purely one color
                        singleColor = True
                        for y2 in range(y, max_y+1):
                            for x2 in range(min_x, max_x+1):
                                if getColor(x2, y2) != currentColor:
                                    singleColor = False
                                    break
                            if not singleColor:
                                break
                        if not singleColor:
                            i += 1

                            # Save the cropped image
                            im.crop((min_x, y, max_x, max_y)).save("out_"+str(i)+".png")
                if color in colors:
                    # Start a line with a relevant color
                    currentColor = color
                    min_x = x
                else:
                    currentColor = None