Pages: [1]   Go Down

Author Topic: What is Capture One's working color space?  (Read 1377 times)

torger

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 3182
What is Capture One's working color space?
« on: February 21, 2017, 04:17:47 AM »

Anyone who knows what the internal color space of Capture One is? Or more precisely, what color space does the RGB color picker show? (which may or may not actually be the "internal color space", but anyway it's that I'm interested in)

I know that the gamma is sort-of 1.8 (actually it's more of an sRGB-variant eg a linear segment plus something else that adds up to approximately gamma 1.8 ), but I don't know what the RGB primaries are. Anyone who knows? Maybe they even vary depending on camera?

The reason I'd like to know is that I'm developing a software that would provide better C1 compatibility if I could match the color space so color picker values match up.
« Last Edit: February 21, 2017, 04:30:20 AM by torger »
Logged

BartvanderWolf

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 6796
Re: What is Capture One's working color space?
« Reply #1 on: February 21, 2017, 05:13:20 AM »

Anyone who knows what the internal color space of Capture One is? Or more precisely, what color space does the RGB color picker show? (which may or may not actually be the "internal color space", but anyway it's that I'm interested in)

I know that the gamma is sort-of 1.8 (actually it's more of an sRGB-variant eg a linear segment plus something else that adds up to approximately gamma 1.8 ), but I don't know what the RGB primaries are. Anyone who knows? Maybe they even vary depending on camera?

I think only the Capture One engineers know, but it's not something as simple as a ProPhoto RGB with linear gamma. From occasional messages from them (on LuLa) it appears to be some sort of adaptive (unbounded) colorspace per camera model that is just large enough to accommodate the gamut that is required for processing (and can be assigned to an export as "camera profile"). I do not know what the coordinates of the RGB primaries are, but presumably one could find out by checking the coordinates in the embedded ICC Camera profile. That should also show if the coordinates are fixed, or variable with required saturation settings or image content for a specific image.

I once tried to fit a single curve (attached) through the TRC values of a profile for my Canon EOS 1Ds Mark III, which showed an average gamma of 0.51478 (1/1.94), but I don't know if that changes depending on image content or not. A Piecewise fitted curve would also allow a better fit, there seems to be a linear slope at low levels.

Cheers,
Bart
Logged
== If you do what you did, you'll get what you got. ==

torger

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 3182
Re: What is Capture One's working color space?
« Reply #2 on: February 21, 2017, 08:21:38 AM »

It's a bit tricky to get linear (=only gamma-encoded) output from C1, as their "linear" curves does often does things to control highlights etc. Rather than TRC from the profile, I think it's more accurate to use the TIFFTAG_TRANSFERFUNCTION tag of TIFFs exported without color management, that is the tag you use to linearize data prior to camera profiling.

I have curve-fitted that with very close result, the constants look pretty ugly complex, but the final function is not too complicated. I don't think it's exactly what they use (which could be just a 1D LUT), but it matches the result of TIFFTRANSFER_FUNCTION really well:

static const double c1_gamma_k = (7 * sqrt(3) * sqrt(5) * sqrt(577) + 648) / 5000.0;
static const double c1_gamma_l = (7 / sqrt(8655));
static const double c1_gamma_k_inv = 5000.0 / (7 * sqrt(3) * sqrt(5) * sqrt(577) + 648);
static const double c1_gamma_l_inv = (7 / sqrt(8655)) * (7 * sqrt(3) * sqrt(5) * sqrt(577) + 648) / 5000.0;

static inline double
c1_gamma_forward(const double x)
{
    if (x <= c1_gamma_l_inv) {
        return x * c1_gamma_k_inv;
    } else {
        return (sqrt(3) * sqrt(28850000 * x - 1397) - 648) / 8655;
    }
}

static inline double
c1_gamma_inverse(const double y)
{
    if (y <= c1_gamma_l) {
        return y * c1_gamma_k;
    } else {
        return 0.8655 * y*y + 0.1296*y + 0.0049;
    }
}

This function is pretty close to 1.8 as they refer to themselves, but has a linear segment in the dark shadows, the same type of design as sRGB gamma has.

Having a gamma that matches is important for my profiling software to work, matching the color picker RGB primaries is only a curiousity though... it surprises me why it's so "secret", surely someone must have asked before? In Lightroom the color picker shows ProPhotoRGB primaries with sRGB gamma in percent. That no answer exists for Capture One could indicate that it indeed is a variable space, although if the working space is variable the color picker could still have it's own fixed color space. It's not important enough for me to reverse-engineer it like the gamma.
Logged

scyth

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 436
Re: What is Capture One's working color space?
« Reply #3 on: February 21, 2017, 09:02:17 AM »

Or more precisely, what color space does the RGB color picker show?

based on "view" -> "proof profile"

if you (probably) interested when "no proof profle" selected there then it still depends on "curve" selected in "base characteristics" and "enable recipe proofing"
« Last Edit: February 21, 2017, 09:14:11 AM by scyth »
Logged

BartvanderWolf

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 6796
Re: What is Capture One's working color space?
« Reply #4 on: February 21, 2017, 09:24:08 AM »

It's a bit tricky to get linear (=only gamma-encoded) output from C1, as their "linear" curves does often does things to control highlights etc. Rather than TRC from the profile, I think it's more accurate to use the TIFFTAG_TRANSFERFUNCTION tag of TIFFs exported without color management, that is the tag you use to linearize data prior to camera profiling.

Yes, also see this (quoted) response from Esben (from Phase One):
http://forum.luminous-landscape.com/index.php?topic=106031.60

Cheers,
Bart
Logged
== If you do what you did, you'll get what you got. ==

torger

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 3182
Re: What is Capture One's working color space?
« Reply #5 on: February 21, 2017, 09:43:23 AM »

based on "view" -> "proof profile"

if you (probably) interested when "no proof profle" selected there then it still depends on "curve" selected in "base characteristics" and "enable recipe proofing"

Ah, I didn't find that, thanks. Yes this was what I was actually after, rather than the working color space, so my question was a bit misleading. I see here in the menu that you can choose between several options and have the colorpicker show sRGB if you want etc.
Logged

scyth

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 436
Re: What is Capture One's working color space?
« Reply #6 on: February 21, 2017, 09:46:29 AM »

Yes, also see this (quoted) response from Esben (from Phase One):
http://forum.luminous-landscape.com/index.php?topic=106031.60

Cheers,
Bart

and then there is a statement "the thing is that we actually do most of the work in the native camera space" but still one need to be sure what curves are applied before RGB numbers displayed... for example one might want to use "linear scientific" curve (.fcrv file where is no instruction to handle data near clipping) instead of "linear"
Logged

ErikKaffehr

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 10624
    • Echophoto
Re: What is Capture One's working color space?
« Reply #7 on: February 21, 2017, 01:53:46 PM »

Hi,

I had the impression that it would display Adobe RGB values, but it seems to be wrong.

What I would like to see was a way of displaying Lab values. I switched Lightroom to display Lab, and I would never go back.

Best regards
Erik
Anyone who knows what the internal color space of Capture One is? Or more precisely, what color space does the RGB color picker show? (which may or may not actually be the "internal color space", but anyway it's that I'm interested in)

I know that the gamma is sort-of 1.8 (actually it's more of an sRGB-variant eg a linear segment plus something else that adds up to approximately gamma 1.8 ), but I don't know what the RGB primaries are. Anyone who knows? Maybe they even vary depending on camera?

The reason I'd like to know is that I'm developing a software that would provide better C1 compatibility if I could match the color space so color picker values match up.

scyth

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 436
Re: What is Capture One's working color space?
« Reply #8 on: February 21, 2017, 02:34:17 PM »

What I would like to see was a way of displaying Lab values.

P1 actually sells C1 CH edition with such capability... for a lot of money

for example = http://dtdch.com/capture-one-ch/
Logged

ErikKaffehr

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 10624
    • Echophoto
Re: What is Capture One's working color space?
« Reply #9 on: February 23, 2017, 03:48:09 PM »

Hi,

I have checked a bit this morning. So I guess it shows RGB values in output colour space. At least is seems it changes a lot when I switch from Adobe RGB to sRGB as output colour space.

I much prefer Lab, though, as it separates Luminance from chromacity.

Best regards
Erik



P1 actually sells C1 CH edition with such capability... for a lot of money

for example = http://dtdch.com/capture-one-ch/

Dinarius

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 933
    • Denis Mortell Photography
Re: What is Capture One's working color space?
« Reply #10 on: March 03, 2017, 03:44:28 AM »

Hi,

I had the impression that it would display Adobe RGB values, but it seems to be wrong.

What I would like to see was a way of displaying Lab values. I switched Lightroom to display Lab, and I would never go back.

Best regards
Erik

In Hasselblad's Phocus, you can choose to display in Lab.

In fact you only have three profile display choices; Input, Output (the colour space you've selected in your file saving profile), and Lab. That's it. Couldn't be simpler.

There is now also an inbuilt Colour Calibration tool. So, no need for expensive third-party plugins.

And it's all free!  8) (Though only useful if you have a Hasselblad camera)

That is why I use mine for some colour critical work.

Totally agree with you on the Lab point.

Capture One is fabulous. I'd never go back to ACR or LR.

But, on the issue of colour, it could do better.

D.
« Last Edit: March 03, 2017, 03:59:49 AM by Dinarius »
Logged

torger

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 3182
Re: What is Capture One's working color space?
« Reply #11 on: March 03, 2017, 06:05:52 AM »

I have checked a bit this morning. So I guess it shows RGB values in output colour space. At least is seems it changes a lot when I switch from Adobe RGB to sRGB as output colour space.

scyth answered a bit back, you can choose "View"->"Proof Profile" in the menu, that defines what the color picker shows. It's always RGB values though as far as I know.

As to what the actual working color space is it seems that it may be varying depending on camera model, noone seems to have an answer to that. It's something large, but not as large as ProPhotoRGB. The working color space is probably specially adapted to get a desirable effect of the RGB-curve and at the same time be large enough to fit a reasonable color range. Lightroom uses ProPhotoRGB primaries, which C1 couldn't because it doesn't really work well with an RGB curve as it exaggerates the curve's inherent hue shifts. Lightroom doesn't use a pure RGB curve though as C1 does, but their own hue-correted version of it so it works fine in ProPhoto.

Why I asked though was to actually know about the RGB values in the color picker, I just incorrectly assumed that it was showing working profile values...
Logged

scyth

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 436
Re: What is Capture One's working color space?
« Reply #12 on: March 03, 2017, 12:09:06 PM »

It's always RGB values though as far as I know.

as noted about CH edition can show lab too...

spaces like cieLCH might be better though or may be even HSV/HSB coordinates-representation of RGB coordinates for some given RGB color space... in a regular C1 you need to painfully go to color editor to see that, very inconvenient

Logged
Pages: [1]   Go Up