How to resize text for cv2.putText according to the image size in OpenCV, Python?

Question

fontScale = 1
fontThickness = 1

# make sure font thickness is an integer, if not, the OpenCV functions that use this may crash
fontThickness = int(fontThickness)

upperLeftTextOriginX = int(imageWidth * 0.05)
upperLeftTextOriginY = int(imageHeight * 0.05)

textSize, baseline = cv2.getTextSize(resultText, fontFace, fontScale, fontThickness)
textSizeWidth, textSizeHeight = textSize

# calculate the lower left origin of the text area based on the text area center, width, and height
lowerLeftTextOriginX = upperLeftTextOriginX
lowerLeftTextOriginY = upperLeftTextOriginY + textSizeHeight

# write the text on the image
cv2.putText(openCVImage, resultText, (lowerLeftTextOriginX, lowerLeftTextOriginY), fontFace, fontScale, Color,
            fontThickness)

It seems fontScale does not scale text according to the image width and height because the text is almost in the same size for different sized images. So how can I resize the text according to the image size so that all the text could fit in the image?

Answer 1

Here is the solution that will fit the text inside your rectangle. If your rectangles are of variable width, then you can get the font scale by looping through the potential scales and measuring how much width (in pixels) would your text take. Once you drop below your rectangle width you can retrieve the scale and use it to actually putText:

def get_optimal_font_scale(text, width):
    for scale in reversed(range(0, 60, 1)):
    textSize = cv.getTextSize(text, fontFace=cv.FONT_HERSHEY_DUPLEX, fontScale=scale/10, thickness=1)
    new_width = textSize[0][0]
    print(new_width)
    if (new_width <= width):
        return scale/10
return 1

Answer 2

for this worked!

scale = 1 # this value can be from 0 to 1 (0,1] to change the size of the text relative to the image
fontScale = min(imageWidth,imageHeight)/(25/scale)

just keep in mind that the font type can affect the 25 constant