Greyscale measurements are inverted?

[J.M]

Hi,

I've got a big problem - I have a colour scale that I setup in a specific colour (in my case a blue).

Now I need to convert this scale to grey values and measure these values.

When I convert the document colour format to "Grey/8" and get the colour picker tool I get mixed CMYK colour values (for example for a 100% K I get C70M66Y66K74) - that shouldn't be because on a document with the colour format "Grey" values with other colours then black shouldn't exist.

Even when I set up a colour value of C00M00Y00K100 and fill an area with that I get C70M66Y66K74 when I measure it with the colour picker tool.

But what confuses me totally - when I set the Colour palette to "Greyscale" I get greyscale values that are inverted - for 100% black I get "Grey: 0". Please have a look at the attached screenshot.

How can I get the clear grey values of these fields you can see in the screenshot. I'm totally lost and don't understand the logic here. Why is grey in a document with the format Grey not grey? I've done this in Photoshop for decades and wondered why I couldn't understand the logic of this in Affinity Photo.

Any help will be highly appreciated. In the meantime I'll have to start up an old Photoshop to measure what I need quickly  

[RichardMH]

The scales % is 100-what you want. 100-73=27.

The Info panel should give what you want if you change to Greyscale colour model.

 

[J.M]

Hi Richard,

thanks for your answer.

I don't understand the logic here. 0% grey = black and 100% grey = white?

It only works, when I set the colour mode to cmyk - when I choose K = 30 then I got 30 % grey.

When I set the colour chooser in Photoshop, Illustrator etc. they set the K value, not the brightness of the color as in the greyscale palette in Affinity. When I set a grey = 30 in Affinity it is K = 70. When I open the info palette in Affinity and set the Colour model to "Greyscale" a K value is shown - 70 in this example.

So this is inconsistant and that confused me. I would expect the K value, not the brightness value. It would be great if there would be an option to set this to the K value.

[Old Bruce]

On 11/29/2022 at 2:49 AM, J.M said:

I have a colour scale that I setup in a specific colour (in my case a blue).

Now I need to convert this scale to grey values and measure these values.

The major problem is going to be Perceptual versus some sort of Grey value from a Colour. For the Perceptual you could use this set of values in a Black and White adjustment.

For a grey version you could convert to Lab and use the Lightness channel's values.

[Lisbon]

50 minutes ago, Old Bruce said:

For the Perceptual you could use this set of values in a Black and White adjustment.

Very useful @Old Bruce

There are some nice things we can do with B&W adjustment set the way you did.

But for visualization purposes i just set the B&W to Colour. Same result.