Hi Alex,
Can you not just change the return value depending on the y position
in the filter? Something like:
return y<pos1?
(formula 1) :
y<pos2?
(formula 2):
y<pos3?
(formula 3) : (formula 4);
At least that's how I tend to do this kind of thing.. although I seem
to remember conditionals being somewhat more limited in core image, so
you have to plan a bit.
Chris
On 22 Dec 2008, at 20:09, Alex Drinkwater wrote:
Hiya,
thanks for getting back to me!
--- On Mon, 22/12/08, Christopher Wright <[email protected]> wrote:
From: Christopher Wright <[email protected]>
Subject: Re: Applying Filter Kernel To Only Part of a Image
To: "Alex Drinkwater" <[email protected]>
Cc: "quartzcomposer-dev list list" <[email protected]
>
Date: Monday, 22 December, 2008, 12:42 PM
Anyone?
Is it possible using JavaScript in a Core Image
Filter patch, to apply a kernel function to only a part of
an input image?
I don't know about it being possible with JS. But I
can go a step lower.
CoreImage Filters apply to an entire image. You can set an
ROI (Region of Interest) to make work on a rectangular
subregion of the image though. You can also set a DOD
(Domain of Definition) to control which parts of the image
are valid/defined.
You can set a filter's "shape" with the
CIFilterShape class, which appears to just represent a
rectangular region (and only one region, not multiple
rectangles).
That's actually what I want, but I can't seem to get it to work. See
below.
So it doesn't look like the underlying CoreImage
functionality supports having filters operate selectively on
several non-contiguous regions of an input image. Thus, I
think it's unlikely that JS will add that automatically.
It would have to be a multipass filter step, to process
each piece.
Ah, that's what I meant, actually. I envisaged a number of passes,
with each pass only working on a part of the image. The reason for
all this is that I have a filter that applies a different variation
of an equation to each of 4 vertical strips of the image. I'm trying
to avoid using the ternary operator to choose which variation to
apply, since this results in all 4 variations being calculated every
every single pixel, which seems massively inefficient.
An alternative might be to use a mask, and have the
filter's code honour the mask. It'll do some extra
work on the masked out regions (that ultimately have no
effect), but it might be faster than doing multipass stuff
in JS/by hand in QC.
That's worth thinking about. I could apply a mask to different
sections each pass, but I'd still need to comp 4 images together as
another pass, something I was hoping to avoid.
Or maybe there's a way to have more than one rectangle,
but I've not seen that anywhere...
Does the ROI allow the filter to be applied to part of the image,
while leaving the rest of the image as it was? This is what I had
assumed, but my experiments so far don't seem to bear that out.
Maybe I have this completely wrong..
This jS code in the JS panel of the CIFilter patch
function __image main(__image image, __color color) {
return multiplyEffect.apply(image.definition, new Vec(0.0,
10.0, 0.0, 10.0), image, color);
}
should, I'd have though, only apply the effect to a small part of
the image, but this doesn't seem to be the case- the effect is
applied to the whole image area.
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