[Image-SIG] Image perspective with PIL

[Edward Cannon]

a,b,c,d,e,f,g,h are the coefficients of the perspective transform.
look at http://alumni.media.mit.edu/~cwren/interpolator/ for a brief
introduction (look for the fraction formula x= (ax+by+c)/(gx=hy+1)

On Sun, May 16, 2010 at 9:51 AM, PyProg PyProg <pyprog05 at gmail.com> wrote:
> 2010/5/3 Fredrik Lundh <fredrik at pythonware.com>:
>
>> I've added the documentation from the original patch to this page:
>>
>>  http://effbot.org/tag/pil.Image.Image.transform
>>
>> The next text is attached below.
>>
>> </F>
>>
>> im.transform(size, PERSPECTIVE, data)
>>
>> im.transform(size, PERSPECTIVE, data, filter)
>>
>> Applies a perspective transform to the image, and places the result
>> in a new image with the given size.
>>
>> Data is a 8-tuple (a, b, c, d, e, f, g, h) which contains the
>> coefficients for a perspective transform. For each pixel (x, y)
>> in the output image, the new value is taken from a position
>> (a x + b y + c)/(g x + h y + 1), (d x + e y + f)/(g x + h y + 1)
>> in the input image, rounded to nearest pixel.
>>
>> This function can be used to change the 2D perspective of the
>> original image.
>
> Hello
>
> The problem is that I do not understand what that means: "which
> Contains the coefficients for a perspective transform ... "... and in
> particular what exactly match a, b, c, d, e, f, g and h.
>
> If you are patient (excuse me), can you explain with precision (and a
> didactic, for someone who has trouble like me) what these data (and
> possibly with an example of processing with good values for a, b, c,
> d, e, f , g and h).
>
> Thank you in advance.
>
> a+
>
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