[Sidefx-houdini-list] cop's log 2 lin

Edward Lam edward at sidefx.com
Fri Jan 9 13:59:37 EST 2009


Here's a link that might help:

http://www.sjbaker.org/steve/omniv/love_your_z_buffer.html

You likely have (uppercase) "z_buffer_value"'s in the image, but want to 
compute the "z" values (ie. distance from eye to the object).

-Edward

Ben Schrijvers wrote:
> No it's more than 8 bit. Though every bit counts in a game engine so in 
> the actual buffer might be more than just Z.
> But I believe this dump image is already processed somehow to stip a 24 
> bit depth value (first 3 bytes) from a 32 buffer.
> It was a .dds file that I loaded into Photoshop and saved as 32 bit tiff 
> file.
> 
> Apart from the "adapt" I also found the histogram to be handy.
> My values now (after calculation below) go from 1 to 50 which sort of is 
> correct for this shot.
> 
> cheers,
> benS
> 
> 
> Peter Robbinson wrote:
>> I wouldn't expect a log image in a game engine, and it will likely be 8 
>> bit as well won't it?
>> When you MMB on one of the cop nodes, what's it telling you?
>>
>> PeterR
>>
>> Ben Schrijvers wrote:
>>   
>>> No I'm looking at a Z-buffer of our game engine.
>>> Not even sure if it's really a log image and the coder went already home 
>>> or are getting drunk downstairs :-)
>>>
>>> I've found that it looks a lot better when I do:
>>> 1 / (1-image)
>>>
>>> cheers,
>>> benS
>>>
>>>
>>> Andrew D Lyons wrote:
>>>   
>>>     
>>>> Is this the kind of image you are dealing with?
>>>>
>>>> http://www.imagemagick.org/www/motion-picture.html
>>>>
>>>> I'd guess you would need to know the black point,white point, and
>>>> gamma with which the image were encoded...
>>>>
>>>> Cheers
>>>>
>>>>
>>>>
>>>> 2009/1/9 Ben Schrijvers <ben.schrijvers at guerrilla-games.com>:
>>>>   
>>>>     
>>>>       
>>>>> Hi there,
>>>>>
>>>>> In COP's how do I convert from a log image to a linear image?
>>>>>
>>>>> I've found a log(x) function in the Function Cop but somehow that gives
>>>>> me negative values.
>>>>> But that probably the wrong way around in that it's lin to log.
>>>>> So what's the inverse? Obviously I've got now idea what I'm talking about...
>>>>>
>>>>> cheers,
>>>>> benS
>>>>>
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>>>>>       
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> 
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