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Compressing PIL image without saving the file

I am having trouble with compressing image in python without saving the image at the disk. The image has a save function as described here. Here it optimizes the image by saving it. Is it possible to use the same procedure without saving the image. I want to do it like another python function.
image=image.quantize() [here it reduces the quality a lot ]
Thanks in advance :)

In PIL or opencv the image is just a large matrix with values for its pixels. If you want to do something with the image(e.g. display it), the function needs to know all the pixel values, and thus needs the extracted image.
However, there is a method to keep the image compressed in memory until you really need to do something with the image. Have a look at this answer: How can i load a image in Python, but keep it compressed?

Extracting small region of image from BMP file in Python

I have a BMP image and I want to extract a small portion of it and save it as a new BMP image file.
I was able to load image and read it however I was not able to extract the small portion of BMP image as I am new to manipulating BMP image with python and also it not same as reading text file.
Things I have to do is
load image.
extract small portion of image.
eg. I have to extract 40X40 pixel image from 900X900 image file
then save extracted image as new file. eg new.bmp
I am trying to do this for last 3 days also I have searched a lot in the net but got solution which uses Pillow library however I need it to do this without using any external module of Python. Stackoverflow is my last hope I need some guidance from a expert people present here, please provide my some guidance.

How to save grayscale image in Python?

I am trying to save a grayscale image using matplotlib savefig(). I find that the png file which is saved after the use of matplotlib savefig() is a bit different from the output image which is showed when the code runs. The output image which is generated when the code is running contains more details than the saved figure.
How can I save the output plot in such a manner that all details are stored in the output image?
My my code is given below:
import cv2
import matplotlib.pyplot as plt
plt.figure(1)
img_DR = cv2.imread(‘image.tif',0)
edges_DR = cv2.Canny(img_DR,20,40)
plt.imshow(edges_DR,cmap = 'gray')
plt.savefig('DR.png')
plt.show()
The input file (‘image.tif’) can be found from here.
Following is the output image which is generated when the code is running:
Below is the saved image:
Although the two aforementioned images denote the same picture, one can notice that they are slightly different. A keen look at the circular periphery of the two images shows that they are different.

Save the actual image to file, not the figure. The DPI between the figure and the actual created image from your processing will be different. Since you're using OpenCV, use cv2.imwrite. In your case:
cv2.imwrite('DR.png', edges_DR)
Use the PNG format as JPEG is lossy and would thus give you a reduction in quality to promote small file sizes. If accuracy is the key here, use a lossless compression standard and PNG is one example.
If you are somehow opposed to using OpenCV, Matplotlib has an equivalent image writing method called imsave which has the same syntax as cv2.imwrite:
plt.imsave('DR.png', edges_DR, cmap='gray')
Note that I am enforcing the colour map to be grayscale for imsave as it is not automatically inferred like how OpenCV writes images to file.

Since you are using cv2 to load the image, why not using it also to save it.
I think the command you are looking for is :
cv2.imwrite('gray.jpg', gray_image)

Using a DPI that matches the image size seems to make a difference.
The image is of size width=2240 and height=1488 (img_DR.shape). Using fig.get_size_inches() I see that the image size in inches is array([7.24, 5.34]). So an appropriate dpi is about 310 since 2240/7.24=309.4 and 1488/5.34=278.65.
Now I do plt.savefig('DR.png', dpi=310) and get
One experiment to do would be to choose a high enough DPI, calculate height and width of figure in inches, for example width_inch = width_pixel/DPI and set figure size using plt.figure(figsize=(width_inch, height_inch)), and see if the displayed image itself would increase/decrease in quality.
Hope this helps.

Save image without rescaling

I have a 2D array and I need to save it as an image. What's the best way to do it without rescaling? I want to read the image afterwards and check that the values have been saved correctly. I am saving it as a bmp so to avoid compression issues, but other formats should also be fine.

To save an image you can use SciPys imsave function.
imsave(path, image)
EDIT: To Save an image as bmp just choose the file extension in path accordingly.
EDIT2: To prevent intensity normalization you can use
scipy.toimage(image, cmin=0, cmax=255, mode='I').save("image.png")
You can use mode'I'to save your image in a specific format. Just be sure that your input is of type uint16.

PIL - empty PSD image

I'm trying to load this PSD image with Python Imaging Library.
http://www.2shared.com/photo/JjSY7dN-/BG1.html
I'm not very familiar with layered images. Can someone check to see what's the issue? The image appears to be completely transparent. Opening it in my image editor I noticed that the only layer in the image was hidden, I could unhide it to see the colors.
When I load the image with PIL, I get the same issue, but it seems that PIL consolidates the layers into one and I can't do the same as in my image editor. Or maybe there's something I don't know.

PIL provides only very rudimentary hooks into the PSD format. It doesn't support writing or much in the way of manipulation. Your image layer is not shown, so it results in a transparent image. You'll need something more advanced to modify the PSD.
Here's all there is about the PSD format in PIL: http://www.pythonware.com/library/pil/handbook/format-psd.htm
Soon to be available here: http://effbot.org/imagingbook/format-psd.htm