Convert Numpy array to image by using OpenCV or PIL

Question

I am trying to convert my array to image using OpenCV or PIL libraries, In both of libraries, I am getting the images with mixed up color.

This is the way I tried convert Numpy array to image using OpenCV :

   for i in range(len(batch_tx)):
        cls_pred = sess.run(y_pred_cls, feed_dict={x: batch_tx})
        cls_true = sess.run(tf.argmax(batch_ty, 1))
        img = cv2.resize(batch_tx[i], (FLAGS.img_size, FLAGS.img_size))
        img = cv2.cvtColor(img.astype(np.uint8), cv2.COLOR_BGR2RGB)
        cv2.imwrite(
            './saveImage/img' + str(i) + ': ' + 'True: ' + str(cls_true[i]) + ', Pred:' +
            str(cls_pred[i]) + '.JPEG', img)

The output is like below image for all my images (This is an image of a ship)

And I have tried PIL library as well and got the same output.

batch_tx[1] is an array of the first image in my dataset and the type is numpy.ndarray with the shape of (96,96,3)

Any Idea?

Thanks in advance.

OpenCV is BGR and not RGB, maybe it is that? PIL uses RGB as far as I remember. You can convert it to BGR with img[:, :, ::-1].copy(). Or load it with PIL with Image.fromarray(img) — api55
– api55, Commented Jun 4, 2018 at 11:20
Just saw that you are converting it to RGB before saving with OpenCV... remove the line with cvtColor... OpenCV imwrite takes BGR images — api55
– api55, Commented Jun 4, 2018 at 11:22
Hey @api55 I want to save my images in RGB, not in BGR that's why I used cvtColor. and As you said I remove that line and I can see my images better but my images are a bit dark. Its look like there is a dark frame in front of images and How can I save images in RGB? — A.M
– A.M, Commented Jun 4, 2018 at 11:43
The images are saved in JPG format, which it has its own specifications, you can save it with OpenCV (BGR) and load it with PIL(RGB) and it will be the same image. But if you save it as RGB with OpenCV it will be store as if it was a BGR image, becuase it has the channels flipped. About the dark part, if you can edit the question an add that new image I may help you, but my guess is the img.astype(np.uint8) used in the cvtColor line may be needed in the imwrite one — api55
– api55, Commented Jun 4, 2018 at 11:54

Jeru Luke · Accepted Answer · 2018-06-04 18:00:20Z

Most of OpenCV functions work only with BGR images and not RGB, for example imshow or imwrite. OpenCV will do the work for you to put it in the correct way and save it as JPG image that can be loaded by ANY other app. If you have it with another order, then the function won't know this and save it with the wrong order.

Removing this line:

img = cv2.cvtColor(img.astype(np.uint8), cv2.COLOR_BGR2RGB)

should do the work for you.

My guess is that is not in the correct format (np.uint8) either, since you use it in the line that I just told you to remove. So you must also change the saving part to:

cv2.imwrite(
            './saveImage/img' + str(i) + ': ' + 'True: ' + str(cls_true[i]) + ', Pred:' +
            str(cls_pred[i]) + '.JPEG', img.astype(np.uint8))

Everything should work now. This images can be loaded in another moment with PIL an any other library as well and you will get almost identical images (JPG is a lossy compression) if you want identical, try saving them in another format that has lossless compression.

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