C#'s WriteAllBytes Equivalent Function in Python

Question

I have an image saved as a bytes array in C#. Below would be an example of how you could create such an array:

byte[] image_bytes= new byte[100] {137, 80, 78, 71, ..., 130};

Note: The above is a simplified example of I achieve the byte array. In reality, I am using Unity to generate the array. Here is a brief snippet on how I actually go about generating the byte array in case this sheds light on latter parts of the question:

camera.Render();
...
Texture2D image = new Texture2D(camera.targetTexture.width, camera.targetTexture.height);
image.ReadPixels(new Rect(0, 0, camera.targetTexture.width, camera.targetTexture.height), 0, 0);
image.Apply();
byte[] image_bytes = image.EncodeToPNG();
...

In C# I can use the function WriteAllBytes to save this image as a file that I can later open on my computer. I have tested this and thus know that the aboveimage_bytes array is not corrupted as I can view the final image image_name.png:

File.WriteAllBytes("image_name.png", image_bytes);

The C# scirpt then sends the byte array as a JSON string over TCP connection to a python script. I have confirmed that the byte array arrives in the python script and has the same length. I have also confirmed that the first and last four bytes are the same, for example:

>>> data = json.loads(message)
>>> img_bytes = np.array(data["image"], dtype=bytes)
>>> print(img_bytes[0])
b'137'
>>> print(img_bytes[1])
b'80'
...
>>> print(img_bytes[-1])
b'130'

My goal is to eventually convert the byte array to an OpenCV frame so I can use OpenCV functions on it. However, I can't even seem to do the basics with it, for example, saving it to a file. When I try to save the data to a file in the python script, the resultant files can not be opened by standard image viewing software. I have tried a basic file save operations:

>>> with open("image_name.png", 'wb') as w:
>>>   w.write(img_bytes)

I have tried using OpenCV:

>>> img_np = cv2.imdecode(img_bytes, cv2.IMREAD_COLOR)
>>> cv2.imwrite("image_name.png", img_np)

I have also tried using PIL (Note: here I used the dimensions of the image):

>>> img_np = Image.frombytes('RGBA', (512, 384), img_bytes, 'raw')
>>> img_np.save("image_name.png")

None of the above Python save functions work (they all create files, but none of the files can be opened and viewed). What am I doing wrong? How can I save the file or even better convert the data to an OpenCV frame in Python?

TLDR: I have a byte array that represents an image in C#. I can save the byte array in C# using WriteAllBytes. I send the byte array to a Python script and have confirmed that it arrives uncorrupted. How can I save the file or even better convert the file to an OpenCV frame in Python?

[Does this answer your question?](https://stackoverflow.com/questions/18367007/python-how-to-write-to-a-binary-file) _"The C# scirpt then sends the byte array as a JSON string over TCP connection to a python script"_ - this sounds horribly inefficient. If possible, it would be better to just send the raw binary data. — ProgrammingLlama, Jul 03 '20 at 01:29
In the future, that's maybe how I will go about it. Right now, I use JSON as there are many other variables being sent; the image is only 1 of them. With regard to this question, the reason I brought up the JSON was to convey that to the best of my knowledge, the python script receives the data uncorrupted from the C# script. I just can't seem to use it in any meaningful way. — Watchdog101, Jul 03 '20 at 01:33
Your `numpy.ndarray` doesn't make sense to me, `dtype=bytes` will make each item a *byte string*. I'm assuming your `data` is a list of ints? Likely, you want `dtype=np.uint8`, but to get the raw bytes, just use `bytes(data)`, which should reproduce the actual bytes you want. — juanpa.arrivillaga, Jul 03 '20 at 02:23
So likely, you want `cv2.imdecode(bytes(data), cv2.IMREAD_COLOR)` — juanpa.arrivillaga, Jul 03 '20 at 02:26
Also, I agree with @John you should probably just be sending the raw data — juanpa.arrivillaga, Jul 03 '20 at 02:29
@juanpa.arrivillaga, thanks I will give this a try and let you know about the dtype, and cv2 code. The reason I don't do raw data is the fact that I need to send other information other than the image, such as the position, orientation of the camera to name a few. I however will look into ways to just send the raw data. — Watchdog101, Jul 03 '20 at 02:58
@juanpa.arrivillaga both the `dtype=bytes` and `dtype=np.uint8` solve the problem. Could you write this up as an answer so that I can mark it as the solution. Thanks so much for the help! — Watchdog101, Jul 03 '20 at 14:01

score 1 · Accepted Answer · answered Jul 03 '20 at 20:06

Using dtype=bytes doesn't make sense. This makes each item a byte string, hence img_bytes[0] isn't. byte 137, it's the byte string b'137, because data["image"] is a list of ints.

So likely, you wanted:

img_bytes = np.array(data["image"], dtype=np.uint8)

But, you can also use:

img_bytes = bytes(data["image"])

C#'s WriteAllBytes Equivalent Function in Python

1 Answers1