[Sidefx-houdini-list] OT: sRGB to linear question

Antoine Durr antoine at floqfx.com
Tue Jul 8 14:49:36 EDT 2008


Hence my point, some packages do it one way, others do it the other  
way.  Only real way to tell is to put a numerically correct grey ramp  
into an image and run it through the various gozintas and gozoutas,  
and see what happens.

-- Antoine


On Jul 8, 2008, at 11:39 AM, Ivan DeWolf wrote:

>
> indeed, this does seem to be why nuke scaled the dali lama correctly;
> nuke (correctly, in this case) assumed the .jpg was sRGB, which it is.
> Houdini assumed it was linear. When I gamma the image by 1/2.2 ,  
> then scale,
> then gamma back to 2.2 it works.
>
> So, houdini's compositor always assumes the input images are  
> linear, which is a
> reasonable assumption in most cases.
>
>
>
> Quoting John Coldrick <jc at axyzfx.com>:
>
>> On Tuesday 08 July 2008 14:09, Edward Lam wrote:
>>> Houdini's compositor doesn't apply gamma correction (or  
>>> "uncorrection").
>>> It doesn't make any assumptions about the image data being read  
>>> in. Thus
>>> you would need to convert it to 16-bit and then to linear (via  
>>> the Gamma
>>> COP) before scaling.
>>
>> 	yeah Nuke, OTOH, *does* make assumptions about incoming images  
>> based on
>> their
>> file format, which I always found practical, perhaps, but dodgy in  
>> concept.
>>
>> At least now with v5 you can set and save that behaviour...
>>
>> 	Cheers,
>>
>> 	J.C.
>>
>>
>> -- 
>> John Coldrick                  www.axyzfx.com        Axyz Animation
>> 416-504-0425                                         477 Richmond  
>> St W
>>                                                      Toronto, ON  
>> Canada
>> jc at axyzfx.com                                        M5V 3E7
>> --------------------------------------------------------------------- 
>> --
>> The best car safety device is a rear-view mirror with a cop in it.
>>   - Dudley Moore
>>
>>
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>
>
> -Ivan
>
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-- Antoine

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