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Re: 答复: [Openexr-devel] question about the tone mapping in OpenEXR
From: |
Florian Kainz |
Subject: |
Re: 答复: [Openexr-devel] question about the tone mapping in OpenEXR |
Date: |
Wed, 18 Oct 2006 19:19:55 -0700 |
User-agent: |
Mozilla Thunderbird 1.0 (X11/20041207) |
The dither() function attempts to reduce banding caused by the
limited bit depth of the OpenGL frame buffer. The function
implements a particularly simple "halftoning" method. For an
introduction to halftoning, please see
http://www.hpl.hp.com/personal/Robert_Ulichney/papers/2000-halftoning-review.pdf
Section 4, Recursive Tesselation explains Bayer dithering.
Haiqin Yang wrote:
> Dear Florian,
>
> Thank you very much for your interpretation. It will help me understand
> the algorithm quickly. Currently, I still have some confuse about the
> function of “dither”. It is just a dithering table. I read from comment
> and know that it is a Bayer pattern. But how to generate these data,
> what are the rules? I have no clear thought about it. Does any article
> interpret it? And where I can get it? Thank you!
>
>
>
> Haiqin
>
> -----邮件原件-----
> 发件人: Florian Kainz [mailto:address@hidden
> 发送时间: 2006年10月17日 11:11
> 收件人: Haiqin Yang
> 抄送: address@hidden
> 主题: Re: [Openexr-devel] question about the tone mapping in OpenEXR
>
>
>
> Hi Haiqin,
>
>
>
> you can find the code for the tone mapping curve in file
>
> exrdisplay/ImageView.cpp, somewhere around lines 239 - 360.
>
> The tone mapping curve is three segments: values from 0 to
>
> kl are unchanged; values between kl and kh are compressed
>
> using a logarithmic curve, and values greater than kl are
>
> clamped to kl. Kl and kh are user-selectable parameters.
>
> Video cameras often have similar tone mapping curves.
>
>
>
> I think the curve works because it does not attempt to compress
>
> arbitrarily large contrast ranges into the small range that can
>
> be displyed on a typical computer monitor. The curve merely
>
> tries to soften the hard transition from values that can be
>
> displayed to values that are slightly larger.
>
>
>
> I should probably mention that the curve produces images that
>
> look rather flat. Most people prefer images that have higher
>
> contrast and color saturation in the mid tones. One simple
>
> way to achieve that would be by applying a power function to
>
> the pixels after the tone mapping curve, e.g.
>
>
>
> screenPixel = pow (toneMap (filePixel), p)
>
>
>
> where p is somewhere around 1.5.
>
>
>
> Florian
>
>
>
>
>
>
>
> Haiqin Yang wrote:
>
>> It seems that the tone mapping in OpenEXR is simple, but effective, but
>
>> I do not know why it can achieve it. Does someone can interpret it or
>
>> give me some docs? Thank you!
>
>>
>
>>
>
>>
>
>> Regards,
>
>>
>
>> Haiqin
>
>>
>
>>
>
>>
>
>>
>
>> ------------------------------------------------------------------------
>
>>
>
>> _______________________________________________
>
>> Openexr-devel mailing list
>
>> address@hidden
>
>> http://lists.nongnu.org/mailman/listinfo/openexr-devel
>
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