Python - Helper Functions for Image IO

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This post contains some useful python helper functions for image IO operations.

The key poitns of these helper functions are:

Use BytesIO so that we don't need to save image to disk then reload it into memory.
Encode images so that we can transfer images through network.
The channel order used in openCV is BGR which is different from more widely used RGB. Therefore, if we use openCV to encode/decode an image, we need to convert the color if necessary.

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import base64
import cv2
import io
import numpy as np
import imageio

def loadImageFromImageBytes(imageBytes):
    npimg = np.fromstring(imageBytes.read(), np.uint8)
    return cv2.cvtColor(cv2.imdecode(npimg, cv2.IMREAD_UNCHANGED), cv2.COLOR_RGB2BGR)

def loadImageFromFlaskFileStorageObject(fileStorageObject):
    npimg = np.fromstring(fileStorageObject.read(), np.uint8)
    return cv2.cvtColor(cv2.imdecode(npimg, cv2.IMREAD_UNCHANGED), cv2.COLOR_RGB2BGR)

def encodeImageUsingBase64(image, fileType='.png'):
    assert "." in  fileType, "File type must include dot(.)"
    return base64.b64encode(cv2.imencode(fileType, image)[1].tostring()).decode('UTF-8')

def encodeImageBytesUsingBase64(imageBytes, fileType='.png'):
    assert "." in  fileType, "File type must include dot(.)"
    return base64.b64encode(imageBytes.read()).decode('UTF-8')

# import matplotlib as mpl; mpl.use("Agg")
# import matplotlib.pyplot as plt

def pltSaveFigToBytes(plt, imageType="png"):
    assert not "." in imageType, "Image type should not contain dot(.)"
    imageBytes = io.BytesIO()
    plt.savefig(imageBytes, format=imageType)
    imageBytes.seek(0)
    return imageBytes

def createGifWithBase64Encoding(frames, duration=1):
    imageBytes = io.BytesIO()
    imageio.mimwrite(imageBytes, frames, format="GIF", duration = duration)
    imageBytes.seek(0)
    return base64.b64encode(imageBytes.read()).decode("UTF-8")

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