[yt-users] volume rendering brightness

[Sam Skillman]

Hi Geoffrey,

Another option, which is outlined in the Advanced Rendering talk from the
workshop, is to use an enhance script to renormalize the image.  This
doesn't require setting the clip variable, and is done as a post-processing
step.  The video of the talk, as well as slides, can be found here (see
Advanced Rendering):
http://yt-project.org/workshop2012/#presentations

It references an enhance.py script, which can be found through the hub,
here:
http://hub.yt-project.org/AnalysisAndVisualization/enhance-your-renderings/

I'd suggest taking a look, as it will also walk you through other advanced
rendering techniques.

Best,
Sam


On Tue, Feb 28, 2012 at 5:50 AM, Britton Smith <brittonsmith at gmail.com>wrote:

> Hi Geoffrey,
>
> The brightness of the total image is basically normalized to the brightest
> pixel.  Occasionally, when you rotate the domain, a single pixel will be
> incredibly bright which will cause the rest of the image to be dim by
> comparison.  You can fix this in with the snapshot call by adding the
> keyword,  clip_ratio=some_float.  This limits the maximum brightness to no
> more than a fixed number of standard deviations from the mean.  I recommend
> you start with a clip ratio of 5 or 6 and play around with it.
>
> Briton
>
> On Mon, Feb 27, 2012 at 7:57 PM, Geoffrey So <gsiisg at gmail.com> wrote:
>
>> Hi volume rendering experts,
>>
>> I was playing around with a density volume render of a tiny cube on my
>> laptop, everything went smoothly, however, I notice a change in "overall"
>> brightness between images when I did a rotation.  I'm not sure how to
>> explain this, but it seems that from images of different angles, sometimes
>> the average brightness is consistent, but sometimes it suddenly drops and
>> the image would look about half as bright, and after a couple frames it
>> would light back up.
>>
>> I'm guessing this is after each image is ray casted, it gets normalized
>> to a certain value, and that value changes depending on the angle?  Is
>> there a way to pin the brightness between images so if I make a movie it
>> won't dim and light up as I rotate?
>>
>> Also I was wondering if I'm the only person to notice this? (the only
>> other post I found about volume render brightness is about AMR cell
>> contributions)
>>
>> From
>> G.S.
>>
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