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Re: Layers and transparency Core Image
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Re: Layers and transparency Core Image


  • Subject: Re: Layers and transparency Core Image
  • From: leenoori <email@hidden>
  • Date: Sun, 24 Dec 2006 18:42:49 +0100

El 23/12/2006, a las 19:43, Scott Stevenson escribió:
First up, thanks for the reply, Scott. Now a couple of clarifications.

On Dec 23, 2006, at 8:12 AM, leenoori wrote:

What Core Image filters would I need to use to take a source image and layer a semi-transparent version of another image on top?

I guess CISourceOverCompositing is part of the solution, but I don't know how to make the overlaid image transparent. I suspect that CIColorMatrix might help but I haven't yet been able to figure out how to use it.

I'd basically like to be able to do this with an arbitrary number of layers.

If I'm reading your question correctly, you don't need a filter for this. Alpha transparency is basic Quartz.


CIImage *image1 = [self imageFromSomewhere];
CIImage *image2 = [self anotherImageFromSomewhere];

[image1 drawAtPoint:point fromRect:rect operation:NSCompositeSourceOver fraction:1.0];
[image2 drawAtPoint:point fromRect:rect operation:NSCompositeSourceOver fraction:0.8];

My understanding of the rationale behind Core Image is that you can chain filters together cheaply and only incur the expense of actually drawing in the last step of the chain, so I would like to be able to do this without actually having to draw, if possible. I don't really want to have to draw each layer separately, especially when the number of layers starts to grow. In the end I intend to pass the resulting image off to something else anyway; I don't want to have to draw myself.


Or are you trying to make the image itself into a sort of filter?

No, I think in it's most basic form what I want to know if how I can take a CIImage and uniformly apply an alpha value to it without actually having to draw it. Like I said, I thought that CIColorMatrix might be the right tack but I don't understand how to use it.


Are you looking for something like CGLayer?

I don't know as CGLayer is new to me but I will check it out. I'm trying to look for the simplest solution at this point to replace my existing code which is all NSImage based. So Core Image seemed like the way to go.


Any chance this is what you need? (the open panel won't open accept .jpg files, btw)
http://developer.apple.com/samplecode/CIAnnotation/

Thanks, I'll take a look at that and see if can help...


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  • Follow-Ups:
    • Re: Layers and transparency Core Image
      • From: leenoori <email@hidden>
References: 
 >Layers and transparency Core Image (From: leenoori <email@hidden>)
 >Re: Layers and transparency Core Image (From: Scott Stevenson <email@hidden>)

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