Are my images Green?

Started 5 months ago | Questions thread
Robin Casady
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Re: Here's the Hitch: LR's develop color gamut is always ProPhoto
In reply to MiraShootsNikon, 5 months ago

MiraShootsNikon wrote:

Hi Robin,

I still think you're mistaken about something, here.

LR does employ a color space to render the bits of your NEF RAW files in the develop module, even before you've exported your NEF as a TIFF or sent it to Photoshop or another external editor. Obviously, Lightroom has to work this way because you're looking at a color photograph on your screen! RAW bits don't become something you can look at unless the various RGB pixel values can be referenced as colors. That's what a color gamut does--it provides the reference that says "these x,y,z values = this color."

In fact (as another poster mentioned above), LR uses the ProPhoto RGB color space to show you your photograph in the develop module. I'm 99.999% sure you can't change this.

However, I do need to add another layer of complication. Your computer monitor can't show you all the colors of which ProPhoto RGB is capable of displaying, right? So when you look at a photograph in the develop module, you're actually seeing a RAW conversion in the ProPhoto RGB color space that's then converted (via the relational colorimetric method, I suspect), to your monitor's / OS's color space.

How do I know this? Because if I use Lightroom's soft proofing feature, LR will show me with "blinkies" where ProPhoto RGB colors exceed my monitor's / OS's color space. (The soft proofing feature can also show you where / how the ProPhoto RGB colors exceed your printer's color space, or any other you select.)

Your test, above, shows that if you open a RAW file in Lightroom (using ProPhoto RGB, because you don't have a choice) and then output that articulation of color to another, smaller color space (or look at it via your monitor's / OS's smaller color space), Lightroom will employ a relational colorimetric method and give you the sRGB or AdobeRGB colors matching the ProPhoto RGB articulation where they're available. That's good to know, but your test doesn't show anything more.

I kicked off this "fork" of the conversation by noting that different color spaces have different shapes, which therefore means that they articulate color differently--that the same RAW bits will look like different colors if different color spaces are used to render them.

To show the difference in how these distinct gamuts translate RAW bits into color, you need to actually see RAW bits as rendered by the different spaces. If Lightroom is a part of your workflow, you can't ever really do that, because Lightroom will always give you the ProPhoto articulation. Sure, maybe you then later output (or soft proof) to a different color space and thereby match the ProPhoto articulation in a different space where the other space has matching colors--but you're always seeing the ProPhoto articulation.

Someone else with more technical knowledge can chime in, here, but I suspect this is one of the big contributing reasons (though certainly not the only reason) why Adobe RAW conversions look so fundamentally different than OEM Nikon conversions--why even the "color calibration" options don't really match OEM Nikon output defaults. If you process RAW in your camera, for example, you're using either an Adobe RGB or an sRGB gamut to translate RAW bits to color, and both Adobe RGB and sRGB are shaped differently than ProPhoto RGB--so the same RAW bits become somewhat different colors.

I know you aren't "interested" in JPEGs, but for the sake of science and understanding the concept at play: shooting a pair of JPEGs in different gamuts and then comparing the articulations is an easy way to see what I'm talking about, here.

(Shooting a few JPEGs once for sh|ts and giggles won't give you the cooties!)

Anyway, good conversation and food for thought!

Thanks very much for the explanations. I'm a bit confused about a couple things.

1. Does Lightroom 5 render the RAW to ProPhotoRGB and then convert it to the output color space when exporting? Or, does it render to ProPhotoRGB only for the monitor and process the RAW data into output color space at export?

2. Why do normal looking photos often have out of gamut colors? This seems to be common to web images with bright colors. Stacy's image below was, I assume, processed in sRGB. The color detail in the flower was not blown out. The image looked normal. Yet almost all of the flower is out of gamut. What does this mean?

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Robin Casady
http://www.robincasady.com/Photo/index.html
"Get your facts first, then you can distort them as you please."
—Mark Twain

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