Scale Blur using Pixel Aspect Ratio

Discussion and Support of Awake, the Fusion plug-in pack
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Chad
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Scale Blur using Pixel Aspect Ratio

Postby Chad » Mon Aug 10, 2009 1:02 pm

Is it possible to scale the blur size based on the Pixel Aspect as opposed to the Pixel Aspect Ratio?

The way it appears to work now, a Pixel Aspect of 12:24 is evaluated the same as a 1:2. I'd prefer it if the actual pixel size was used, not the ratio.

I'm attaching a setting to demonstrate this. I would expect that turning the Scale on or off would result in similar blurring, but it doesn't.

- Chad
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AwakeScalingExample_A01_.setting.txt
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myurick
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Re: Scale Blur using Pixel Aspect Ratio

Postby myurick » Mon Aug 10, 2009 3:51 pm

I believe the intent of the "Scale Blur using Pixel Aspect Ratio" is to allow you to keep a symmetric blur on your image when the pixels are non-square. To that end, I would expect that turning that option on and off would change the shape of the blurring kernel (the dimensions of which are being scaled inversely by the aspect ratio) and you'd get a different blur. It'll be more symmetric with the option checked, and distorted in one direction the more non-square the pixels are when unchecked.

That said, after a glance at the code, the blur kernel appears to be getting scaled by the actual pixel values. That would explain why you would notice such a large discrepancy between turning that option on/off. The kernel dimensions are being scaled inversely by those 12:24 values, making the kernel quite small. This can be counteracted by ramping up the blur size to account for it. You can make a small black image with a single white pixel in the middle to examine the impulse response of the filter (if you are into that sort of thing). It should confirm the above comments.

I'm not sure if that kind of scaling was intended or not... I can certainly take a look at changing how it works if it's not intuitive. But I think it should be possible to achieve any desired result by adjusting the blur size, or by unchecking the "Lock Blur Size X/Y" and adjusting them independently. Or am I misunderstanding the problem?

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Chad
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Re: Scale Blur using Pixel Aspect Ratio

Postby Chad » Mon Aug 10, 2009 4:32 pm

I think it's backwards...

In the example I sent, a FqBl (Scale Blur on) applied after the Man, set to 40, looks very similar to a FqBl (Scale Blur on) applied after the Scl set to 400 (40*10).

If you uncheck the Scale Blur using Pixel Aspect Ratio, then 40 on both looks similar. But in both cases the blur is 2x too strong in the X axis.

- Chad

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myurick
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Re: Scale Blur using Pixel Aspect Ratio

Postby myurick » Mon Aug 10, 2009 5:42 pm

Hmmm, well, it doesn't look to be too far off from what the Blur operator is doing. In fact, if I compare the impulse response of the FrequencyBlur to the Blur operator, both set to Gaussian mode, they are pretty darn close. That's if I enable the "Scale Blur using Pixel Aspect Ratio" option, since the Blur operator appears to account for that by default. I have to adjust the blur sizes differently to get them to match up, but using the same source image/pixel aspect for both, I get nearly the same result. Neither appears to be distorted in the X direction.

If I swap in a Blur operator after that Mandelbrot, instead of the FrequencyBlur, it looks pretty much the same once I scale it up to about 1000.

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Chad
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Re: Scale Blur using Pixel Aspect Ratio

Postby Chad » Tue Aug 11, 2009 5:02 am

The Blur tool seems to care only for the width of the image, not the scale of it. So a blur on an image that is 200 pixels wide, where each pixel is 10 units wide should be essentially a blur on image 2000 units wide. Likewise, applying a blur to an image 2000 pixels wide, where each pixel is 1 unit wide should be the equivalent. But it isn't. You have to scale the 200 pixel blur up by a factor of 10.

So best I can tell, the Blur tool doesn't take the pixel scale into account. I would prefer that the Blur tool did, but I'll take that up with Eyeon. It's something that can be done per tool, though, and it's largely a matter of mapping the UI sliders to the internal kernels and functions.

- Chad

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myurick
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Re: Scale Blur using Pixel Aspect Ratio

Postby myurick » Tue Aug 11, 2009 5:46 am

Ah ok, I misunderstood. I thought your issue was with the aspect ratio of the kernel, but you don't like the way they are using a relative blur size for the kernel. Have you tried using the 'Absolute' option of the 'Blur Size Unit' in the FrequencyBlur? I think that may give you the result you are looking for.

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Chad
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Re: Scale Blur using Pixel Aspect Ratio

Postby Chad » Tue Aug 11, 2009 9:50 am

The Absolute mode just lets me scale the kernel by the number of pixels as opposed to the width of the image. Good to have (especially when working with cropped ROI for interactivity), but you still have to scale that value by the pixel scale just the same as with the Relative mode.

- Chad

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myurick
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Re: Scale Blur using Pixel Aspect Ratio

Postby myurick » Wed Aug 12, 2009 4:28 am

Alright, I'll take a look at adding another option for that case.


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