CODEWITHSUNDEEP
pythonimageopencvbyte
xercool
xercool

Reputation: 943

Python OpenCV load image from byte string

I'm trying to load image from 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 create temporary file for working with images in PyOpenCV.

NOTE: need cv (not cv2) wrapper function

Upvotes: 65

Views: 176563

Answers (5)

jabaldonedo
jabaldonedo

Reputation: 26572

This is what I normally use 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','rb')
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)

I have added the conversion from numpy.ndarray to cv2.cv.iplimage, so the script above will print:

<type 'str'>
<type 'numpy.ndarray'>
<type 'cv2.cv.iplimage'>

EDIT: As of latest numpy 1.18.5 +, the np.fromstring raise a warning, hence np.frombuffer shall be used in that place.

Upvotes: 146

kym
kym

Reputation: 1183

One gotcha of imdecode:

If the buffer is too short or contains invalid data, the function returns [None]

This feels uncharacteristically lenient from OpenCV. Here's a function that accommodates for this:

import numpy as np
import cv2 as cv

def read_image(content: bytes) -> np.ndarray:
    """
    Image bytes to OpenCV image

    :param content: Image bytes
    :returns OpenCV image
    :raises TypeError: If content is not bytes
    :raises ValueError: If content does not represent an image
    """
    if not isinstance(content, bytes):
        raise TypeError(f"Expected 'content' to be bytes, received: {type(content)}")
    image = cv.imdecode(np.frombuffer(content, dtype=np.uint8), cv.IMREAD_COLOR)
    if image is None:
        raise ValueError(f"Expected 'content' to be image bytes")
    return image

Upvotes: 3

Eypros
Eypros

Reputation: 5723

I was following the solution from @jabaldonedo but it seems it's a bit old and need some adjustments.

I am using OpenCV 3.4.8.29 by the way.

im_path = 'path/to/foo.jpg'
with open(im_path, 'rb') as fp:
    im_b = fp.read()
image_np = np.frombuffer(im_b, np.uint8)
img_np = cv2.imdecode(image_np, cv2.IMREAD_COLOR)  

im_cv = cv2.imread(im_path)

print('Same image: {}'.format(np.all(im_cv == img_np)))

Same image: True

Upvotes: 10

Anugraha Sinha
Anugraha Sinha

Reputation: 660

I think this answer provided on this stackoverflow question is a better answer for this question.

Quoting details (borrowed from @lamhoangtung from above linked answer)

import base64
import json
import cv2
import numpy as np

response = json.loads(open('./0.json', 'r').read())
string = response['img']
jpg_original = base64.b64decode(string)
jpg_as_np = np.frombuffer(jpg_original, dtype=np.uint8)
img = cv2.imdecode(jpg_as_np, flags=1)
cv2.imwrite('./0.jpg', img)

Upvotes: 32

Alexandre Mazel
Alexandre Mazel

Reputation: 2558

I've try to use this code to create an opencv from a string containing a raw buffer (plain pixel data) and it doesn't work in that peculiar case.

So here's how to do that for this kind of data:

image = np.fromstring(im_str, np.uint8).reshape( h, w, nb_planes )

(but yes you need to know your image properties)

if your B and G channel is permuted, here's how to fix it:

image = cv2.cvtColor(image, cv2.cv.CV_BGR2RGB)

Upvotes: 10

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