How to make SnapChat Lenses? – Hacker Noon

Let us try to implement a SnapChat filter on the below picture of Dwayne Johnson. We will add a pair of glasses and a mustache for the purpose of this tutorial.

First, import all the required libraries:

import cv2
import numpy as np
import glob
import os
import dlib

Read all the image files that we want to overlay on the face of Dwayne Johnson. We will use the glasses and mustache shown below.



In the code snippet below, we load the mustache and glasses images and create our image masks. The image masks are used to select sections from an image that we want to display. When we overlay the image of a mustache over a background image, we need to identify which pixels from the mustache image should be displayed, and which images from the background image should be displayed. The masks are used to identify which pixels should be used when applied to an image.

We load the mustache/glasses with -1 (negative one) as the second parameter to load all the layers in the image. The image is made up of 4 layers (or channels): Blue, Green, Red, and an Alpha transparency layer (knows as BGR-A). The alpha channel tells us which pixels in the image should be transparent and which one should be non-transparent (made up of a combination of the other 3 layers). Then we take just the alpha layer and create a new single-layer image that we will use for masking. We take the inverse of our mask. The initial mask will define the area for the mustache/glasses, and the inverse mask will be for the region around the mustache/glasses. Then we convert the mustache/glasses image to a 3-channel BGR image. Save the original mustache/glasses image sizes, which we will use later when resizing the mustache/glasses image.

imgMustache = cv2.imread("mustache.png", -1)
orig_mask = imgMustache[:,:,3]
orig_mask_inv = cv2.bitwise_not(orig_mask)
imgMustache = imgMustache[:,:,0:3]
origMustacheHeight, origMustacheWidth = imgMustache.shape[:2]
imgGlass = cv2.imread("glasses.png", -1)
orig_mask_g = imgGlass[:,:,3]
orig_mask_inv_g = cv2.bitwise_not(orig_mask_g)
imgGlass = imgGlass[:,:,0:3]
origGlassHeight, origGlassWidth = imgGlass.shape[:2]

Once the reading is done. Let’s start with face detection. There are several ways to do that.

  1. dlib face detection
  2. OpenCV face detection
  3. TenesorflowSSD face detection

I am going to use dlib face detection over other two for 2 reasons.

  1. To use Tensorflow we need to train our own face detection model as there is no pre-trained model available.
  2. dlib seems to give better accuracy compared to OpenCV.
# 68 point detector on face
predictor_path = "shape_predictor_68_face_landmarks.dat"
# face detection modal
face_rec_model_path = "dlib_face_recognition_resnet_model_v1.dat"
predictor = dlib.shape_predictor(predictor_path)

dlib 68 point detector will detect following face points

dlib face points map

Now we will start capturing frames from the webcam or from a video file and after that we will detect faces in those frames also will detect 68 points on the face to apply filters.

ret, frame =  
dets = cnn_face_detector(frame, 1)
for k, d in enumerate(dets):
shape = predictor(frame, d.rect)

Now points 31 and 35 are nose length so we will consider mustache as 3 times the length of nose, and height is relevant to the original picture. Apply that numpy array to original frame.

mustacheWidth = abs(3 * (shape.part(31).x - shape.part(35).x))
mustacheHeight = int(mustacheWidth * origMustacheHeight / origMustacheWidth) - 10
mustache = cv2.resize(imgMustache, (mustacheWidth,mustacheHeight), interpolation = cv2.INTER_AREA)
mask = cv2.resize(orig_mask, (mustacheWidth,mustacheHeight), interpolation = cv2.INTER_AREA)
mask_inv = cv2.resize(orig_mask_inv, (mustacheWidth,mustacheHeight), interpolation = cv2.INTER_AREA)
y1 = int(shape.part(33).y - (mustacheHeight/2)) + 10
y2 = int(y1 + mustacheHeight)
x1 = int(shape.part(51).x - (mustacheWidth/2))
x2 = int(x1 + mustacheWidth)
roi = frame[y1:y2, x1:x2]
roi_bg = cv2.bitwise_and(roi,roi,mask = mask_inv)
roi_fg = cv2.bitwise_and(mustache,mustache,mask = mask)
frame[y1:y2, x1:x2] = cv2.add(roi_bg, roi_fg)

Now, let’s put on glasses. Points 1 and 16 will be glass width, and height is relative.

glassWidth = abs(shape.part(16).x - shape.part(1).x)
glassHeight = int(glassWidth * origGlassHeight / origGlassWidth)
glass = cv2.resize(imgGlass, (glassWidth,glassHeight), interpolation = cv2.INTER_AREA)
mask = cv2.resize(orig_mask_g, (glassWidth,glassHeight), interpolation = cv2.INTER_AREA)
mask_inv = cv2.resize(orig_mask_inv_g, (glassWidth,glassHeight), interpolation = cv2.INTER_AREA)
y1 = int(shape.part(24).y)
y2 = int(y1 + glassHeight)
x1 = int(shape.part(27).x - (glassWidth/2))
x2 = int(x1 + glassWidth)
roi1 = frame[y1:y2, x1:x2]
roi_bg = cv2.bitwise_and(roi1,roi1,mask = mask_inv)
roi_fg = cv2.bitwise_and(glass,glass,mask = mask)
frame[y1:y2, x1:x2] = cv2.add(roi_bg, roi_fg)

read original article here