Python OpenCV load image from byte string

Question

I'm trying to load image from a string like as PHP function imagecreatefromstring

How can I do that?

I have MySQL blob field image. I'm using MySQLdb and don't want to create a temporary file for working with images in PyOpenCV.

NOTE: need cv (not cv2) wrapper function

Answer 1

You can easily use this to convert images stored in database to OpenCV images in Python:

import numpy as np

import cv2

from cv2 import cv

# Load image as string from file/database

fd = open('foo.jpg')

img_str = fd.read()

fd.close()

# CV2

nparr = np.fromstring(img_str, np.uint8)

img_np = cv2.imdecode(nparr, cv2.CV_LOAD_IMAGE_COLOR) # cv2.IMREAD_COLOR in OpenCV 3.1

# CV

img_ipl = cv.CreateImageHeader((img_np.shape[1], img_np.shape[0]), cv.IPL_DEPTH_8U, 3)

cv.SetData(img_ipl, img_np.tostring(), img_np.dtype.itemsize * 3 * img_np.shape[1])

# check types

print type(img_str)

print type(img_np)

print type(img_ipl)

After this, add the conversion from numpy.ndarray to cv2.cv.iplimage, so the above script will print:

<type 'str'>

<type 'numpy.ndarray'>

<type 'cv2.cv.iplimage'>

If you want to learn python, visit this python tutorial and python course.