Incorrect RGB Values

[Jakub Trybowski]

I have an HP Envy X360 15,6" OLED and the latest version of Windows 10 Pro with all the latest stable updates, as well as the latest version of Designer.

I have a problem with Designer displaying incorrect RGB values, which don'y agree with their corresponding CMYK values.

 

For example, the red values used in the gradients in the attached file are:

R: 204 G: 34 B: 40  

 

C: 0 M: 100 Y: 100 K: 0

However, when I click on any red stop, I cat an incorrect RGB value of R: 219 G: 1 B: 0.

I've tried reinstalling and resetting the app (I invoked the settings reset menu by holding Ctrl while starting the app), to no avail.

oceanus_icons_export.afdesign

Edited October 11, 2021 by Jakub Trybowski

[Paul Mc]

There is no guaranteed equivalence between any colour in the RGB and CMYK colour spaces. There are many RGB colours outside of the CMYK gamut but which can be reproduced in RGB on-screen. Lots of RGB values hit the limits of what can be created using CMYK, especially very saturated colours. In an unbiased colour space CMYK of 0,100,100,0 would almost certainly be equivalent to, or pretty close to, an RGB value of 255,0,0 so 219,1,0 is not far off - perceptually. Where did you get the 204,34,40 value? Those are high Blue and Green components for a CMYK colour with no Cyan in it. Also, on-screen colour values are often gamma corrected values which adds to the confusion.

[Alfred]

When I inspect the attached file in AD on iPad the red stop is shown as CMYK (0, 100, 100, 0). Switching to RGB gives me (219, 1, 0) and switching back to CMYK gives me (0, 100, 100, 14).

If I set the red stop to RGB (204, 34, 40) and switch to CMYK it gets translated to (0, 84, 80, 20).

[Jakub Trybowski]

40 minutes ago, Paul Mc said:

Where did you get the 204,34,40 value? Those are high Blue and Green components for a CMYK colour with no Cyan in it. 

In Designer, I set the CMYK values to 0, 100, 100, 0 and then switched from CMYK to RGB in the Color tab.

In other words, Designer interpretes C:0 M:100 Y:100 K:0 as R:204, G:34, B:40, which is in total disagreement with what I get using this converter:

https://www.ginifab.com/feeds/pms/cmyk_to_rgb.php

I simplys assumed that Designer correctly converted colors from CMYK to RGB and HEX.

[NotMyFault]

Really interesting. When you try this on Win / Ipad, Designer and Photo, you get totally different results.

Create new VGA file with CMYK / U.S. Web Coated (SWOP v2) profile

From CMYK 0,100,100,0  to RGB

iPad Designer: 255/0/0

W10 Designer: 237/28/36

W10 Photo: 218/56/50 (both in color panel and info panel)

iPad Photo: 255/0/0

[NotMyFault]

Even more wired:

You can use the levels adjustment as a kind of probe where no info panel is available (Designer, Photo on iPad).

• Paint with brush to get a big red area.
• Add a levels adjustment.
• Just move the sliders for C and K and see that there is nor change in rendering. This proves that C and K are not part of the color.

Even when info panel and color panel say something else.

[Jakub Trybowski]

Wow, those colors are pretty inconsistent. 😮

I wonder how Illustrator and Photoshop would handle this?

Would we get CMYK 0, 100, 100, 0 --> RGB 255, 0, 0 or some other value?

[Paul Mc]

You are missing some information in this discussion and that is the profile of the display device or medium. Please check out the first two pages of this document: https://support.dma.ucla.edu/help/tutorials/print_color_guide.pdf It is a simplified version of what is happening. The gamuts of RGB and CMYK vary depending on the display device, and, although they overlap, not all RGB values can be represented in CMYK. This means that an RGB colour "converted" to CMYK is likely to be an approximation and for saturated colours may be a "best effort" in terms of approximating that colour but could be way off. CMYK colours are invariably darker and less saturated than the RGB originals and many RGB colours don't have a CMYK equivalent.

Here is a simplified conversion formula:

Red = 255 × ( 1 - Cyan ÷ 100 ) × ( 1 - Black ÷ 100 )
Green = 255 × ( 1 - Magenta ÷ 100 ) × ( 1 - Black ÷ 100 )
Blue = 255 × ( 1 - Yellow ÷ 100 ) × ( 1 - Black ÷ 100 )

But this makes no allowance for the capabilities of the target device or medium to display the colours. Normally RGB has a wider gamut than CMYK so this direction is usually OK. The other direction is a little more complicated but is usually an approximation because the colours involved hit the limits of the inks or pigments available on the device. These limits are wrapped up in a profile which is information that defines the capabilities of a screen or printer. Every display device and printer has a profile and these are often different making the conversion between them somewhat unpredictable. Your results from the tests are interesting. Clearly the iPad is using the unrestricted gamut conversion formula (above) whereas the others are using something to scale and shift the values which is normally the result of converting between two different profiles.

[Jakub Trybowski]

I work almost exclusively in the CMYK color space - since I design logos - so I'm actually well aware of it's limitations.

Speaking of profiles, my laptop has a wide-gamut display - with a 95-96% coverage of the Adobe RGB color space and an average delta E of 0.6-0.8 - calibrated to D65 or 6500K, 80 cd/m2, a gamma value of 2.2 and a standard gamma curve, using an X-Rite i1 Display Pro Plus and Calibrite CC Profiler (formerly X-Rite i1 Profiler). 

In Designer, I use the US SWOP CMYK profile.

[Sean P]

10 hours ago, Jakub Trybowski said:

Wow, those colors are pretty inconsistent. 😮

I wonder how Illustrator and Photoshop would handle this?

Would we get CMYK 0, 100, 100, 0 --> RGB 255, 0, 0 or some other value?

When converting CMYK to RGB the document's colour profile is used for the conversion to give a more accurate colour value that is within the gamut of that profile. As PaulMc has said most web based converters don't take any consideration of colour profile into the conversion.

I've just taken a document in Illustrator using US Web Coated SWOP v2 with a 0,100,100,0 CMYK value and that gives me an RGB of 227, 6, 19
Doing the same in Designer again using US Web Coated SWOP v2 gives me an RGB of 237, 28, 36. Obviously the two have different conversion algorithms so won't give the exact same values.

See attached video. Also just to comment on NotMyFault's point - the iPad uses a different method for conversion that was considered faster for the iPad/Metal at the time. Looking at the results I suspect this isn't taking the document's profile into consideration so is using the same conversion as the web based ones. This is something we do have logged with development as a difference between the platforms.