BSC Film and Digital Image Evaluation 2009

[Gavin Greenwalt]

Yep.

Speaking of which my PCI-E slot situation is going to get pretty dire here in the not too distant future.

 

[Sanjin Jukic]

Lin and Log are not color spaces. They are methods of value coding, with a log representation using a gamma curve. A color space is defined by a color gamut and white point, not by whether the file the information is saved in is Log or Lin. Moving visual information between color spaces definitely yields different results.

Saying that Lin and Log are not color space are a bit confusing....

LINK>>>

"Linear vs. Log:
Linear space means the computer values are incremented in the typical way. On an 8 bit system (256 values) 128 would be half the value of 256.
This half exposure would be equivalent to 1 film f-stop. Stepping through this progression 256, 128, 64, 32, 16, 8, 4, 2, 1 is equal to 1 f-stop per number. This means that the dark end has very course increments and the high end has very fine increments.
This is opposite to the perceptual sensitivity of the human eye.

If the image is in log color space then each f-stop is the same number of values. 32, 64, 96, 128, 160, 192, 224, 256.
This provides better response in the dark end of the spectrum and doesn't waste it on the dark end. 8 bit log image is a close equivalent to a 12 bit image.

If the color space being described is a linear color space, then an equal portion of the bits are used to describe colors in each section of the color spectrum. In a logarithmic color space, the same bits can be used to emphasize details in the white and black areas of an image.
Logarithmic color mapping is a more accurate way of describing the great detail that is captured in film, which is highly responsive in areas of extreme dark and light.

In short: log images are optimized for the perceptual range of the human eye."

LINK>>>


Now it couldn divide us as Log and Lin guys/girls.

Divide et Impera. (Divide and rule.)

So:

Are you Log guy/girl (he/she prefers a film look)?

Or you are Lin guy/girl (he/she prefers a video look)?

 

[Sanjin Jukic]

"LINEAR

Linear color space = physical color space
Physics provides headaches but it also provides laws to understand the behaviour of light.
Formulas used by engineers to manipulate images are coming from physics. So they are designed to work well in the linear color space.
They work not so bad in others color spaces so many people don't understand the interest to invest in mastering use of linear color space.
The interest is to get best results.

Format designed to use linear color space by default

Open EXR (.exr)
But it does not mean every Open EXR is storing linear data.

If you work in linear

Don't work in 8 bits depth per channel.


Pros

Once understood, you can get better results in lighting and compositing.


Cons

You must use a software with color management to see properly your images.
You must unlearn the parameters of your "classic lights" when using "physical lights".
Physical lights / physical shaders

If formulas are designed to work in linear space, why "classic parameters" of lights don't work ?
Because of the speed of computers at the beginning of CG.
Computers were so slow it was not possible to use the equations without big approxiations and big sacrifices "hacking" these equations (ex: specular and reflections).
The habit of using hacks lead to disconnections beetween some techniques and the physical world (By the way, most of these hacks were needed,
better to have something not perfect than nothing). But the main idea behind most of these formulas is coming from physics.
Now faster computers allow techniques to go back closer to the reality (ex: global illumation)."

"LOG

Log color space = film scan color space
How to recognize if an image is stored in log ?

An image stored in log will appear TOO WASHED if you display it in a software without color management.
So 95% of the time you'll see an image obviously too washed (without color management), you can assume it is stored in log.

Formats designed to use log color space by default

Cineon (.cin or number padded with 4 digit without extension)
Dpx (.dpx)


If you work in log

If you're manipulating images in log without converting them first to linear (or sometimes to sRGB),
you're probably doing a mistake or you work on a dedicated software/hardware able to handle natively log plates.
If it is the second option you probably don't need to read this page so I'll go for the first option : mistake.


Proper use of log images

Log images are images coming from film scanners. They are designed to carry as much information possible about color.
Don't see them as directly usable images but more as "archives" (like zip or tar.gz files).
Once converted in linear (equivalent to unzipped), you can work with the images.
This conversion is often done on the fly in compositing softwares.
Once the work finished you need to reconvert it in log to be able to shoot them on film."

More>>>Color Space 101>>>

 

[Gavin Greenwalt]

So:
Are you Log guy/girl (he/she prefers a film look)?
Or you are Lin guy/girl (he/she prefers a video look)?

:emote_hanged:

Just stop saying that and I won't have any disagreement.

Look has nothing to do with the file's data layout. And every image encoding method eventually gets converted to linear light photons. So to say the advantage of log is that it "looks right" is just the result of how most software is written. It's not an inherent advantage to the file.

Photoshop has instilled an entire generation with bad habits because of the way it (doesn't) handle different colorspaces.

There is a lot going on behind the scenes that's completely transparent to the user. If you wanted you could calibrate your entire computer so that linear images look correct on your monitor by default. And most monitors aren't calibrated to display log images out of the box either. So either way you're going to need a lut to view log or lin images. Not really an advantage one way or the other.

The only real empirical differences are the file size and available file formats (and the properties of the various file formats).

:beatdeadhorse5:

edit: also that book scan is really confusing because they're mixing up lin and srgb as the same thing.

Saying that Lin and Log are not color space are a bit confusing....

It's confusing either way.

YUV, RGB, CMYK: those are all color spaces in one sense.

But while lin and log are unique from one another they can encompass the same 'color space'. i.e. you can have Rec709 saved out as lin or log. Then again sRGB tends to include its gamma curve in its definition so lin and sRGB are sort of in different color spaces but not.

He was correct in correcting me on that one.

 

[Sanjin Jukic]

One more video from BSC Camera Evaluation July 2009 (It's audience recorded footage of the BSC event.):

BSC Camera Evaluation July 2009: Shot with 35mm Kodak 500T

BSC Camera Evaluation July 2009: Shot with RED ONE

BSC Camera Evaluation July 2009: Shot with Arri D-21

BSC Camera Evaluation July 2009: Shot with SI-2K


"Multi format camera test. This video is a shaky audience type and only for the close-up section of the presentation.
Obviously the quality isn't as good as the real thing but you can spot the differences across the formats.
Other tests were daylight interior and exterior and night time interior and exterior.
Also de-grained 16mm with Arri's new Relativity software which was very effective.
No such alternative processing for digital though.

Commentary from Sue Gibson, present President of BSC"

Actually they were making fun of RED(!!!???),

watch and listen at this web video:

HD USER MAGAZINE tagged BSC Camera Evaluation July 2009 (Vimeo)>>>