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scale was Re: [pygame] Proposed additions to Transform: connected components, upper and lower thresholding, and centroids



hi,

have you tried transform.smoothscale?

cheers,

On Tue, Jun 17, 2008 at 12:19 PM, Chris <c4@xxxxxxxxxxxxxxxxxxxxxx> wrote:
> The gimp uses an image resize function that is perfect.  I use it in PHP
> with my online shop images. Going from larger to smaller, of course.  I had
> hoped that transform would operate the same way but the image degradation
> is... noticeable to severe.
>
> Excuse me if I missed the discussion target.
>
> René Dudfield wrote:
>>
>> Hello,
>>
>> a few notes below.
>>
>>
>> On Tue, Jun 17, 2008 at 10:49 AM, Nirav Patel <olpc@xxxxxxxxxxxxxx> wrote:
>>>
>>> As part of my project to add computer vision stuff to pygame, I'd like
>>> to write a function or functions that do the following.
>>>
>>> For vision purposes, it would be very useful to have thresholding with
>>> both upper and lower boundaries, returning both the number of pixels
>>> within the threshold and the centroid of those pixels.  This is a
>>> trivial addition to the existing transform.threshold() function, but
>>> is it acceptable to modify the input options and the output of an
>>> existing function?  Would it break compatibility with existing pygame
>>> games?  Would it make sense to have a second function so similar to an
>>> existing one?
>>>
>>
>> You could modify the existing function if the old functionality stays
>> the same.  Probably by adding another default argument.  We try not to
>> break existing functionality.
>>
>> I think the current one can use just one distance from the color.  So
>> it's both a lower, and upper threshold.  I'm just wondering if it
>> could be used already to do what you want?
>>
>>> The other function, which is also similar (and could even just be an
>>> option in thresholding), is thresholding with connected component
>>> detection.  This would involve supplying an upper and lower threshold,
>>> a Surface, and optionally a mask.  The function would find the largest
>>> blob of pixels in the Surface within the threshold, make a mask of
>>> those pixels if desired, and return the centroid and number of pixels
>>> in the blob.
>>>
>>
>> Currently this can sort of be done by making a mask from the
>> thresholded image.  Mask has a get_bounding_rect() function.  Doing
>> the get_bounding_rect on a mask turns out to be fast because you
>> process way less data -- as mask is 1 bit per pixel.  Then you can
>> sort the bounding rects on size to find the largest one.
>>
>> I'm not sure if that will be suitable for your task though, but I
>> think maybe you could do things this way.
>>
>>
>>> It could also be useful to have multiple connected component
>>> detection, for "multi-touch" without having to use different colored
>>> objects (or if you are using IR LEDs like the Wii does), but I'm not
>>> sure how to handle that in a single pass of the array.  Actually, I'm
>>> not really sure how I'm going to handle both detection and creating a
>>> mask in a single pass either.  It may be necessary to store the
>>> starting pixel, ending pixel, and size of each connected component on
>>> the first pass, keeping track of which was the largest yet, and then
>>> have a shorter second pass to create the mask that only starts at the
>>> starting pixel and ends at the ending pixel.
>>>
>>
>> Multiple areas can be found like above with Mask.get_bounding_rect().
>>
>> Doing everything in one pass is hard... but if you reduce the data
>> down -- by using a mask -- then the second pass can act on 32x less
>> data.
>>
>> eg, a 1024x1024 image:
>>>>>
>>>>> (1024 * 1024 * 4) / 32.
>>
>> 131072.0
>>
>> So that is 4MB on the first pass down to 131KB of data to process on
>> the second pass.
>>
>>
>>
>>> Any comments, reality checks, questions, or suggestions would be
>>> greatly appreciated.
>>>
>>> Nirav
>>>
>>
>
>