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How to decode jpg image from memory?

I can read a jpg image from disk via PIL, Python OpenCV, etc. into a numpy array via some built-in functions such as (in the case of OpenCV) arr= cv2.imread(filename).
But how do I decode a jpg in binary format directly from memory?
Use case: I want to put a jpg image into a database in binary format and then read it from the db into memory and decode it to a numpy array.
Is this possible?

Assuming that you are storing the image data in your db as a string, you first need to construct a numpy array from that string that can later be converted to an image using cv2.imdecode. For example:
img = cv2.imdecode(np.fromstring(img_data, dtype=np.uint8), cv2.IMREAD_UNCHANGED)

for Python3 use this way:
from scipy import misc
import io
f = open('file.png', 'rb')
fs = f.read()
likefile = io.BytesIO(fs)
face1 = misc.imread(likefile)
Python2 has StringIO.

Fetching Images from Url to Jpg
import requests
from io import BytesIO
response = requests.get("https://optse.ztat.net/teaser/ES/CW15_ES_bermuda_men.jpg")
my_img_In_byts = BytesIO(response.content).read()
path="C:/Users/XX/Desktop/TryingPython/downloadedPic.jpg"
my_fprinter = open(path, mode='wb')
print( my_fprinter .write(my_img_In_byts))
my_fprinter.close()
print("Done")

Convert images in a compressed file such as a zip file to numpy array in python

We could combine module zipfile.ZipFile and PIL.Image.open to read the image from the compressed file. However, we might receive an error io.UnsupportedOperation: seek after we call PIL.Image.open. It refers to the condition that I passed a ZipExtFile object to PIL.Image.open function as below:
from zipfile import ZipFile
from PIL import Image
zipf = ZipFile(path, "r")
f = zipf.open("test.jpg")
img = Image.open(f)
So, how to fix the problem?

Actually we could solve this problem by reading the content of the image and then convert it to cStringIO buffer. The code is below:
from zipfile import ZipFile
from PIL import Image
zipf = ZipFile(path, "r")
# read instead of open
content = zipf.read("test.jpg")
img = Image.open(cStringIO.StringIO(content))

In python 3.7 ZipExtFile objects now support seek operations. If you upgrade to python 3.7.2 or newer, then your code should work.

How to perform JPEG compression in Python without writing/reading

I'd like to work directly with compressed JPEG images. I know that with PIL/Pillow I can compress an image when I save it, and then read back the compressed image - e.g.
from PIL import Image
im1 = Image.open(IMAGE_FILE)
IMAGE_10 = os.path.join('./images/dog10.jpeg')
im1.save(IMAGE_10,"JPEG", quality=10)
im10 = Image.open(IMAGE_10)
but, I'd like a way to do this without the extraneous write and read. Is there some Python package with a function that will take an image and quality number as inputs and return a jpeg version of that image with the given quality?

For in-memory file-like stuff, you can use StringIO.
Take a look:
from io import StringIO # "import StringIO" directly in python2
from PIL import Image
im1 = Image.open(IMAGE_FILE)
# here, we create an empty string buffer
buffer = StringIO.StringIO()
im1.save(buffer, "JPEG", quality=10)
# ... do something else ...
# write the buffer to a file to make sure it worked
with open("./photo-quality10.jpg", "w") as handle:
handle.write(buffer.contents())
If you check the photo-quality10.jpg file, it should be the same image, but with 10% quality as the JPEG compression setting.

Using BytesIO
try:
from cStringIO import StringIO as BytesIO
except ImportError:
from io import BytesIO
def generate(self, image, format='jpeg'):
im = self.generate_image(image)
out = BytesIO()
im.save(out, format=format,quality=75)
out.seek(0)
return out
StringIO is missing in Python3.0, ref to : StringIO in python3

How can a Pygame surface be converted to an image file say a jpeg or a png WITHOUT writing the file to disk? Say after a screen grab? [duplicate]

I have generated an image using PIL. How can I save it to a string in memory?
The Image.save() method requires a file.
I'd like to have several such images stored in dictionary.

You can use the BytesIO class to get a wrapper around strings that behaves like a file. The BytesIO object provides the same interface as a file, but saves the contents just in memory:
import io
with io.BytesIO() as output:
image.save(output, format="GIF")
contents = output.getvalue()
You have to explicitly specify the output format with the format parameter, otherwise PIL will raise an error when trying to automatically detect it.
If you loaded the image from a file it has a format property that contains the original file format, so in this case you can use format=image.format.
In old Python 2 versions before introduction of the io module you would have used the StringIO module instead.

For Python3 it is required to use BytesIO:
from io import BytesIO
from PIL import Image, ImageDraw
image = Image.new("RGB", (300, 50))
draw = ImageDraw.Draw(image)
draw.text((0, 0), "This text is drawn on image")
byte_io = BytesIO()
image.save(byte_io, 'PNG')
Read more: http://fadeit.dk/blog/post/python3-flask-pil-in-memory-image

sth's solution didn't work for me
because in ...
Imaging/PIL/Image.pyc line 1423 ->
raise KeyError(ext) # unknown
extension
It was trying to detect the format from the extension in the filename , which doesn't exist in StringIO case
You can bypass the format detection by setting the format yourself in a parameter
import StringIO
output = StringIO.StringIO()
format = 'PNG' # or 'JPEG' or whatever you want
image.save(output, format)
contents = output.getvalue()
output.close()

save() can take a file-like object as well as a path, so you can use an in-memory buffer like a StringIO:
buf = StringIO.StringIO()
im.save(buf, format='JPEG')
jpeg = buf.getvalue()

With modern (as of mid-2017 Python 3.5 and Pillow 4.0):
StringIO no longer seems to work as it used to. The BytesIO class is the proper way to handle this. Pillow's save function expects a string as the first argument, and surprisingly doesn't see StringIO as such. The following is similar to older StringIO solutions, but with BytesIO in its place.
from io import BytesIO
from PIL import Image
image = Image.open("a_file.png")
faux_file = BytesIO()
image.save(faux_file, 'png')

When you say "I'd like to have number of such images stored in dictionary", it's not clear if this is an in-memory structure or not.
You don't need to do any of this to meek an image in memory. Just keep the image object in your dictionary.
If you're going to write your dictionary to a file, you might want to look at im.tostring() method and the Image.fromstring() function
http://effbot.org/imagingbook/image.htm
im.tostring() => string
Returns a string containing pixel
data, using the standard "raw"
encoder.
Image.fromstring(mode, size, data) =>
image
Creates an image memory from pixel
data in a string, using the standard
"raw" decoder.
The "format" (.jpeg, .png, etc.) only matters on disk when you are exchanging the files. If you're not exchanging files, format doesn't matter.

How to write PNG image to string with the PIL?

I have generated an image using PIL. How can I save it to a string in memory?
The Image.save() method requires a file.
I'd like to have several such images stored in dictionary.

You can use the BytesIO class to get a wrapper around strings that behaves like a file. The BytesIO object provides the same interface as a file, but saves the contents just in memory:
import io
with io.BytesIO() as output:
image.save(output, format="GIF")
contents = output.getvalue()
You have to explicitly specify the output format with the format parameter, otherwise PIL will raise an error when trying to automatically detect it.
If you loaded the image from a file it has a format property that contains the original file format, so in this case you can use format=image.format.
In old Python 2 versions before introduction of the io module you would have used the StringIO module instead.

For Python3 it is required to use BytesIO:
from io import BytesIO
from PIL import Image, ImageDraw
image = Image.new("RGB", (300, 50))
draw = ImageDraw.Draw(image)
draw.text((0, 0), "This text is drawn on image")
byte_io = BytesIO()
image.save(byte_io, 'PNG')
Read more: http://fadeit.dk/blog/post/python3-flask-pil-in-memory-image

sth's solution didn't work for me
because in ...
Imaging/PIL/Image.pyc line 1423 ->
raise KeyError(ext) # unknown
extension
It was trying to detect the format from the extension in the filename , which doesn't exist in StringIO case
You can bypass the format detection by setting the format yourself in a parameter
import StringIO
output = StringIO.StringIO()
format = 'PNG' # or 'JPEG' or whatever you want
image.save(output, format)
contents = output.getvalue()
output.close()

save() can take a file-like object as well as a path, so you can use an in-memory buffer like a StringIO:
buf = StringIO.StringIO()
im.save(buf, format='JPEG')
jpeg = buf.getvalue()

With modern (as of mid-2017 Python 3.5 and Pillow 4.0):
StringIO no longer seems to work as it used to. The BytesIO class is the proper way to handle this. Pillow's save function expects a string as the first argument, and surprisingly doesn't see StringIO as such. The following is similar to older StringIO solutions, but with BytesIO in its place.
from io import BytesIO
from PIL import Image
image = Image.open("a_file.png")
faux_file = BytesIO()
image.save(faux_file, 'png')

When you say "I'd like to have number of such images stored in dictionary", it's not clear if this is an in-memory structure or not.
You don't need to do any of this to meek an image in memory. Just keep the image object in your dictionary.
If you're going to write your dictionary to a file, you might want to look at im.tostring() method and the Image.fromstring() function
http://effbot.org/imagingbook/image.htm
im.tostring() => string
Returns a string containing pixel
data, using the standard "raw"
encoder.
Image.fromstring(mode, size, data) =>
image
Creates an image memory from pixel
data in a string, using the standard
"raw" decoder.
The "format" (.jpeg, .png, etc.) only matters on disk when you are exchanging the files. If you're not exchanging files, format doesn't matter.