On Wed, Oct 17, 2012 at 4:37 PM, Stéfan van der Walt <stefan@sun.ac.za>wrote:

On Wed, Oct 17, 2012 at 7:39 AM, Schönberger Johannes <hannesschoenberger@gmail.com> wrote:

...

Sounds good. Do you have a paper or any reliable source about this? Just interested in this...

The question is, should we make this a decorator, or simply provide it as utility functions? I'm wondering, because now we already have two different ways of handling color images: split them up, RGB, or convert them to LAB and apply the filter to LAB. How do we expose both of these sensible alternatives to the user?

We can have a *default*, so that all single-channel filters are done on the luminance layer, but then combine that with utility functions. E.g.

@luminance_filter def gray_filter(image, ...): ...

gray_filter(color_image, params) --> convert to LAB, filter on L, convert back filter_layers(color_image, gray_filter, params) -> filter each layer separately and combine

Alternatively, skip the decorators completely, and just provide two utility functions: filter_layers and filter_luminance.

I'm not really sure how a utility function would work. Wouldn't you need to provide at least 2 utility functions when converting to LAB: image, ab = prepare_rgb(image) # ... code to generate `filtered_image` from `image` filtered_image = finalize_rgb(filtered_image, ab) Here, `ab` would be some dummy value if the input image is already gray. This is actually a bit cryptic in order to prevent special-casing for RGB images. Otherwise, you'd have to add some conditionals as well. And don't even know how the layer-by-layer approach would work as a utility function. Basically, that's all to say that I think a decorator makes a lot more sense in this case. In fact, you can handle the different behaviors (layer-by-layer vs lightness channel) by either introducing a parameter to decorator or the wrapped filter (or both---the decorator parameter would set the default, which you could override at runtime). Here's a mock up adding a parameter to the filter: https://gist.github.com/3909400 The edge filter example is a bit strange: if you filter by lightness (Oops, I called it "luminance" in the example), then you get weird results. -Tony