Added LogLuvLoader.

[Mugen87]

Related issue: #22757

Description

This PR introduces LogLuvLoader which allows to load HDR images in the LogLuv TIFF format.

The code uses parts of UTIF for parsing TIFF images and a custom toRGBA() method to extract HDR texels in linear RGB color space. The default texture type is half float. Using single precision float is supported.

[Mugen87]

https://raw.githack.com/Mugen87/three.js/dev59/examples/webgl_loader_texture_logluv.html

For comparison:

https://raw.githack.com/Mugen87/three.js/dev59/examples/webgl_loader_texture_rgbm.html
https://raw.githack.com/Mugen87/three.js/dev59/examples/webgl_loader_texture_hdr.html
https://raw.githack.com/Mugen87/three.js/dev59/examples/webgl_loader_texture_exr.html

[mrdoob]

Nice! Seems like the best way to compare them is to put the slider at 0.02. Logluv seems are nice looking as hdr but a bit more orangy.

[Mugen87]

BTW: Depending on the feedback in #22757 (comment) I'll change the RGB color conversion matrix which will lead to a slight hue shift.

[Mugen87]

Using the matrix from the respective paper for now: http://www.anyhere.com/gward/papers/jgtpap1.pdf

[mrdoob]

Now it looks kind of pale... Is that normal?

[Mugen87]

TBH, I'm not yet 100% sure which color conversion matrix is the correct one. But according to the paper and UTIF.jss implementation it is the CIE RGB matrix. Let's wait with a merge until this detail is clear...

[Mugen87]

Wait, the numbers in the matrix were not correct! Now it looks better and similar to our existing HDR examples:

https://raw.githack.com/Mugen87/three.js/251f8e1748ebbeabdca1ae17e35a286b6a5cc7f2/examples/webgl_loader_texture_logluv.html

[WestLangley]

three.js does not currently handle color space accurately.

But, for the purpose of doing something reasonably-consistent, we can assume we want to convert to linear-sRGB color space -- i.e., the sRGB primaries and the D65 white point, without the gamma correction.

So, I would assume the correct matrix to use is the sRGB matrix.

The three.js working color space is implicitly linear-sRGB.

[Mugen87]

I don't think this would be correct. Sticking to the specification of the paper produces the result I have originally expected (meaning a result comparable and consistent to other HDR loaders). Using the sRGB matrix produces a wrong hue shift.

[mrdoob]

Sounds like this is good enough for now 😊

[mrdoob]

Thanks!