[Image-SIG] Saving 16bit tiffs

[Scott Rifkin]

Following up my previous post with another question:

I tried using fromstring and tostring instead of putdata.

Here are the functions:

def image_to_array(image):
    #returns a Numeric array from an Image using getdata
    return reshape(array(image.getdata()), (image.size[1], image.size[0]))

def array_to_image(matrix, mode = 'I;16'):
    #returns an Image from a Numeric array using fromstring(Image) and tostring(Numeric)
    return Image.fromstring(mode, (matrix.shape[1], matrix.shape[0]), ravel(matrix.astype(Int)).tostring())



>>>mat=RandomArray.randint(0,60000,(6,4)) #an array of random ints 0-60000
>>>im=array_to_image(mat)
>>>mat_from_im=image_to_array(im)

now when I look at the matrices (or at the images) there are columns of 
zeros interspersed.  for example (I've substituted letters for the numbers 
to make it more readable...there is no O, anything that looks like that is 
a zero)

>>>mat
    array([[A,B,C,D],
           [E,F,G,H],
           [I,J,K,L],
           [M,N,P,Q],
           [R,S,T,U],
           [V,W,X,Y]])

>>>mat_from_image
    array([[A,0,B,0],
           [C,0,D,0],
           [E,0,F,0],
           [G,0,H,0],
           [I,0,J,0],
           [K,0,L,0]])

note that if I change the width of the array mat to an odd number (say a
6x3 matrix), the are no longer columns but are in positions 
(0,1),(1,0),(1,2),(2,1)...every other number if you were to ravel it.

The problem is making the strings.  When I look at what is returned by 
mat.tostring(), I get a string like '\xe9\x98\x00\x00\x1c\x81\x00\x00...
I can make a new string by just cutting out all the \x00\x00 repeats and 
then reconstruct the image using Image.fromstring(), and this gives me the 
correct image.

My questions are, why is it padding wthe string ith the extra \x00\x00 in 
the first place?  What are these to/fromstring() functions doing? There 
must be a more appropriate way to do this, how?

Thanks much.
Scott Rifkin