Clarity

[Matthew Trentacoste]

Doing the computation per RGB channel would introduce chromatic shifts.  My
guess is that chromatic scaling is probably uniform (either across channels
or  adjusting the saturation of the image in a non-spatially variant
manner).

Some of the best of breed work on this topic is by Sylvain Paris, a
researcher also at Adobe:
http://people.csail.mit.edu/sparis/publi/2011/siggraph/

You can use it to boost certain spatial scales to increase local contrast
and reconstruct an image without artifacts.


On Thu, Oct 24, 2013 at 6:45 PM, Juan Nunez-Iglesias <jni.soma at gmail.com>wrote:

> Thanks Josh, Jerome,
>
> Actually what I'm really after is a good, *local* foreground/background
> correction. The local bit is what attracted me to Clarity even though it's
> not really what I'm after.
>
> Particularly of interest is something that will be robust to artifacts in
> the images.
>
> Juan.
>
> On Fri, Oct 25, 2013 at 10:13 AM, Josh Warner <silvertrumpet999 at gmail.com>wrote:
>
>> I think that's on the right track.
>>
>> But a naive contrast mask affects only the luminance. In the first
>> example the colors are also very punched up; just looking this seems like
>> more than a simple global contrast mask.
>>
>> My guess? They're applying the equivalent of a contrast mask, but to each
>> RGB channel separately. This is "wrong" from an image processing
>> perspective, but in the world of Instagram it seems people are more
>> interested in filters than reality.
>>
>> I wouldn't be against this for advertising purposes, though I'd never do
>> it to my own images.
>>
>> On Thursday, October 24, 2013 2:03:22 AM UTC-5, Jerome Kieffer wrote:
>>
>>> On Thu, 24 Oct 2013 17:27:55 +1100
>>> Juan Nunez-Iglesias <jni.... at gmail.com> wrote:
>>>
>>> > Hi guys,
>>> >
>>> > Does anyone here have any ideas about what the Camera+ Clarity filter
>>> is
>>> > doing? Some examples of the filter
>>> > here<https://secure.flickr.**com/photos/pierrewikberg/**6983939966/<https://secure.flickr.com/photos/pierrewikberg/6983939966/>>and
>>>
>>> > here <http://obamapacman.com/2011/**03/enhance-iphone-camera-**
>>> clarity-video/<http://obamapacman.com/2011/03/enhance-iphone-camera-clarity-video/>>.
>>>
>>> >
>>> > Might be a nice addition to skimage.exposure... =)
>>>
>>> Looks like a contrast mask:
>>> http://www.gimp.org/tutorials/**ContrastMask/<http://www.gimp.org/tutorials/ContrastMask/>
>>>
>>> Here is an old implementation, starting from a JPEG:
>>>     def contrastMask(self, outfile):
>>>         """Ceci est un filtre de debouchage de photographies, aussi
>>> appelé masque de contraste,
>>>         il permet de rattrapper une photo trop contrasté, un contre
>>> jour, ...
>>>         Écrit par Jérôme Kieffer, avec l'aide de la liste python at aful,
>>>         en particulier A. Fayolles et F. Mantegazza avril 2006
>>>         necessite numpy et PIL.
>>>
>>>         @param: the name of the output file (JPEG)
>>>         @return: filtered Photo instance
>>>         """
>>>
>>>         try:
>>>             import numpy
>>> #            import scipy.signal as signal
>>>         except:
>>>             logger.error("This filter needs the numpy library available
>>> on https://sourceforge.net/**projects/numpy/files/<https://sourceforge.net/projects/numpy/files/>")
>>>
>>>             return
>>>
>>>         t0 = time.time()
>>>         dimX, dimY = self.pil.size
>>>
>>>         ImageFile.MAXBLOCK = dimX * dimY
>>>         img_array = numpy.fromstring(self.pil.**tostring(),
>>> dtype="UInt8").astype("**float32")
>>>         img_array.shape = (dimY, dimX, 3)
>>>         red, green, blue = img_array[:, :, 0], img_array[:, :, 1],
>>> img_array[:, :, 2]
>>>         #nota: this is faster than desat2=(ar.max(axis=2)+ar.min(**axis=2))/2
>>>
>>>         desat_array = (numpy.minimum(numpy.minimum(**red, green), blue)
>>> + numpy.maximum(numpy.maximum(**red, green), blue)) / 2.0
>>>         inv_desat = 255. - desat_array
>>>         blured_inv_desat = self._gaussian.blur(inv_desat, config.**ContrastMaskGaussianSize)
>>>
>>>         bisi = numpy.round(blured_inv_desat).**astype("uint8")
>>>         k = Image.fromarray(bisi, "L").convert("RGB")
>>>         S = ImageChops.screen(self.pil, k)
>>>         M = ImageChops.multiply(self.pil, k)
>>>         F = ImageChops.add(ImageChops.**multiply(self.pil, S),
>>> ImageChops.multiply(**ImageChops.invert(self.pil), M))
>>>         exitJpeg = op.join(config.**DefaultRepository, outfile)
>>>         F.save(exitJpeg, quality=80, progressive=True, Optimize=True)
>>>         try:
>>>             os.chmod(exitJpeg, config.DefaultFileMode)
>>>         except IOError:
>>>             logger.error("Unable to chmod %s" % outfile)
>>>         exifJpeg = Exif(exitJpeg)
>>>         exifJpeg.read()
>>>         self.exif.copy(exifJpeg)
>>>         exifJpeg.comment = self.exif.comment
>>>
>>> --
>>> Jerome Kieffer <goo... at terre-adelie.org>
>>>
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-- 

[  matthew m trentacoste                                     ]
[                                                            ]
[  mt at matttrent.com                                          ]
[  http://matttrent.com                                      ]
[  twitter: @matttrent                                       ]
[  +1.415.326.3226                                           ]
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