Parameters messed up in Custom Kernel (or is it me ?)

• Subject: Parameters messed up in Custom Kernel (or is it me ?)
• From: Bjoern Kriews <email@hidden>
• Date: Thu, 18 Aug 2005 14:51:55 +0200
• Delivered-to: email@hidden
• Delivered-to: email@hidden

Hi,

I am looking into another phenomenon:

After weird effects in my custom kernels I tried to
track down why my math always seemed to be wrong - somehow my
input (float) parameters did not contain the values that were visible
in QC.

I tracked it down to two examples, each trying to mark an image
(a gradient in the examples) using a black threshold.

The problems I experience seem very much like those that Michel Schinz
described in this post:

I am using a PB G4 15" 1.67 and it is reproducible on both the internal
LCD and a Cinema Display.

Any help appreciated, Bjoern

------------

File: realParameterpost.qtz

This composition has a kernel that generates a mask with:

kernel vec4 blackMask(sampler image, float minLevel, float realMinLevel)
{
    __color t = sample(image, samplerCoord(image));

    float v = ( t.r + t.g + t.b) / 3.0;

    return v < minLevel ? vec4(1.0) : vec4(0.0);
}

The minLevel Parameter does not influence the output at all while
realMinLevel (which is not touched in the code) does what minLevel
was intended to do.

-------------

file: parameterInfluencePost.qtz

    float v = ( t.r + t.g + t.b) / 3.0;

    return v < minLevel ? vec4(1.0,0,0,1.0) : t;
}

This is nearly the same but generates not a mask but an image.
Here the realMinLevel Parameter works like minLevel should but
the minLevel leads to the gradient being colored - which
is another topic that I'd be _very_ grateful for someone to explain.

Attachment: parameterInfluencePost.qtz
Description: application/quartzcomposer

Attachment: realParameterPost.qtz
Description: application/quartzcomposer

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