What I was thinking was that somewhere around line 214 of jpeginput.cpp, right
after the ImageSpec has been created, you would add
m_spec.attribute ("jpeg:subsampling", ...);
where the string value you set is based on data from the jpeg compressor
(m_cinfo) that reveals the subsampling rates.
On Oct 18, 2014, at 1:37 AM, Justin Israel <[email protected]> wrote:
> I figured I would jump onto this while I have your attention on the topic :-)
> https://github.com/OpenImageIO/oiio/pull/978
>
> I've kept it at YCrCb across the board, per suggestion.
>
> Can you point me at where the extra work should be added to the reader, to
> support the copy() functionality you mentioned? This is my first time digging
> into the plugin code, so I am not too familiar with where I should add that
> bit.
>
> Thanks!
> - Justin
>
>
>
> On Sat, Oct 18, 2014 at 9:12 AM, Larry Gritz <[email protected]> wrote:
> Fine by me.
>
>
> On Oct 17, 2014, at 12:10 PM, Jonathan Gibbs <[email protected]> wrote:
>
>> On Fri, Oct 17, 2014 at 10:26 AM, Larry Gritz <[email protected]> wrote:
>> That's another possibility I would entertain -- automatically upgrading the
>> subsampling when a sufficiently high quality is requested.
>>
>> This seems too magical to me. Those who are setting subsampling levels are
>> probably expert users and probably thus want what they are asking for
>> explicitly.
>>
>> I set the default quality for jpeg output (if no "quality" attribute is
>> found) quite high, 98. I'm also happy to revisit whether that's too much. I
>> can't say it was a principled reason for that particular value.
>>
>> Back when we used 8-bit jpegs in production, they were quality 98, and we
>> moved over time from 4:2:0 to 4:4:4. When we used "16-bit" jpegs (actually
>> 12-bits internally) we used 4:4:4 and quality of 75. Some tests determined
>> that quality of 75 in 16/12-bit looked as good as 98 in 8-bit.
>>
>> Anyway, just data points using jpeg images in animation production.
>>
>> I'd vote the default to be 4:2:0 since that's what most devices write. Those
>> who want 4:4:4 are more likely to understand these settings.
>>
>> --jono
>>
>>
>
> --
> Larry Gritz
> [email protected]
>
>
>
>
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--
Larry Gritz
[email protected]
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