Explanation for ddepth parameter in cv2.filter2d() opencv?

Question

import cv2
import numpy as np
from matplotlib import pyplot as plt

img = cv2.imread('logo.png')

kernel = np.ones((5, 5), np.float32) / 25
dst = cv2.filter2D(img, -1, kernel)
plt.subplot(121), plt.imshow(img), plt.title('Original')
plt.xticks([]), plt.yticks([])
plt.subplot(122), plt.imshow(dst), plt.title('Averaging')
plt.xticks([]), plt.yticks([])
plt.show()

I was trying smoothing a picture and i didnt understand the ddepth parameter of cv2.filter2d() where the value is -1. So what does -1 do and also what does ddpeth mean ?

Answer 1

ddepth

ddepth means desired depth of the destination image

It has information about what kinds of data stored in an image, and that can be unsigned char (CV_8U), signed char (CV_8S), unsigned short (CV_16U), and so on...

type

As for type, the type has information combined from 2 values:

image depth + the number of channels.

It can be for example CV_8UC1 (which is equal to CV_8U), CV_8UC2, CV_8UC3, CV_8SC1 (which is equal to CV_8S) etc.

Further Readings

For more discussion, it can be found in the following two articles

• image type vs image depth
• Matrix depth equals 0
• Detailed - Fixed Pixel Types. Limited Use of Templates

Answer 2

You can see in the doc that ddepth stands for "Destination depth", which is the depth of result (destination) image.

If you use -1, the result (destination) image will have the same depth as the input (source) image.