Remove whitespace of a image python opencv

October 16, 2022

I want to select a rectangular box from a image where all the content is placed. In other words I want remove the background of the image with unimportant(pixels which are not related to content) pixels. How ever the output image should be a rectangle.

What is the easiest way to do this in Python OpenCV?
(I will import files from a folder… Better if I could automate the process)

>Solution :

I hope what you asking is "Crop out the white spaces of image automatically".
Here we assume a binary image : pixels have high and low values.

def focusToContent(img):
    img_ = 255*(img < 128).astype(np.uint8) 
    coords = cv.findNonZero(img_) # Find all non-zero points (text)
    x, y, w, h = cv.boundingRect(coords) # Find minimum spanning bounding box
    
    rect = img[y:y+h, x:x+w] # Crop the image - note we do this on the original image
    rect_originalSized = cv.resize(rect,(img.shape))
    return rect_originalSized

img should be a opencv image (numpy array with proper data type)

Test the code

#testing
img = cv.imread(r"D:/ENTC/SEM_4/EN2550 - Fundamentals of Image Processing and Machine Vision/~images/int-rec/test/1650009171.5083215.png",0)
assert img is not None
focused = focusToContent(img)

fig,ax = plt.subplots(1,2)
ax[0].imshow(img,cmap="gray")
ax[1].imshow(focused,cmap="gray")
plt.show()