1. Write a program that draws a cross mark over the whole image, with a thickness of 3 pixels and in the color red.
2. Create a window with a trackbar to change the ksize of a medianBlur function. The possible range for the kszise value should be between 3 and 99.
3. Perform a gradient morphological operation on an image, considering a kernel size of 7 and a rectangular  morphological shape for the structuring element.
4. Using cvtColor, convert a color image to grayscale and make sure only the darkest 100 shades of gray are filtered out using the threshold function. Make sure that filtered pixels are set to white in the result image and the rest of the pixels are set to black.
5. Use the remap function to resize an image to half of its original width and height, thus preserving the aspect ratio of the original image. Use a default border type for the extrapolation.
6. a) Use colormaps to convert an image to grayscale. b) Convert an image to grayscale and invert its pixels at the same time.
7. Did you read about perspective transformation functions? Which OpenCV function covers all similar transformations in one single function?