Colour Replacement Brush Problems. Does it work at all?

[SolihullRog]

As a frustrated new user of Affinity 2.5.7 I decided to use the Colour Replacement Brush (CRB) to confirm whether I was going mad.

I used a well known picture of Robin Whalley's to conduct a controlled test.  I wonder if anyone can explain some things.  Pictures attached.

1. My main settings for the CRB are Opacity = Flow = Hardness = 100%.  Tolerance = 10%.  Sample Continuously = blank.

2. Open the picture - A.

3. Select CRB.

4. Click on brightest yellow swatch to choose replacement colour.

5. Move cursor over bright red ship.

6. The "cursor circle" (CC) briefly turns brown.  To choose to replace as brown?

7. Press LH mouse down and drag around ship.  Results in a partly-brown ship.  So replacing a red hue by bright yellow equals brown?

8. Click the mouse over the bright red swatch to return bright red ship to bright red.

9. Click over bright red part of ship and brush over brown parts of ship.  Bright red plus yellow plus bright red has resulted in dark red!!!

10. The tool is called the Colour Replacement Brush.  I've read all about that it should be called the Hue Replacement Brush.

11. Even if it is a Hue Replacement Brush, how do I change the ship to a yellow hue?

12. Resulting picture - B - shows result of replacing bright red to bright yellow, then to bright red, then to bright yellow again

13. I finally tried to replace with a blue 'hue' and got purple!!! Picture C.

[NotMyFault]

The brush replaces the hue, but keeps the luminosity.

This might be unexpected for you but is documented in help and has been discussed before

 

https://affinity.help/photo2/en-US.lproj/pages/Painting/replaceClrs.html

L Using the Color Replacement Brush Tool

The Color Replacement Brush Tool takes a sample of the color under the cursor when you begin to paint, and will replace all closely matching colors along the stroke with the current Foreground color. The targeted color's hue will be replaced with the current Foreground color's hue, while retaining saturation and lightness values of the original pixels.

 

 

[SolihullRog]

I am aware of those facts but cannot understand.

I have taken 3 further pictures - D, E, F.

D is the same as the original A.  But it includes a bright red blob, created by CRB, which is invisible.

E contains the picture with the blob being coloured bright yellow.  The blob appears brown WITH A FLAVOUR OF GREEN.  Are you suggesting the this blob is simply dark yellow?

F contains the same blob over but a bright red diagonal sripe has been painted across the blob.  The stripe is noticeably darker than the ship.

Can you explain why the CRB change in F has not resulted as per the CRB change in D?

 

 

[SolihullRog]

I'm sorry that the blob in the middle picture is not consistent but I hope you understand the point.

[NotMyFault]

Use the info panel, set to HSL mode. Add as many as required, an place them to relevant spots. Make a „before“ screenshot. Use CRB. Make another screenshot.
You will see that the H (hue) will take the hue from your chosen color, and S and L will remain unchanged.

[SolihullRog]

Clarification. Three pictures attached G, H, I.

G contains a CRB blob of the brightest red in the swatches.  (It's invisible).

H contains the blob overwritten by the brightest yellow.

I contains the blob overwritten by the brightest red over the yellow.

Somple question.  Why is the blob visible on I but not on G?

Thanks for all replies.

I'm sorry I haven't done the HSL mode check yet, as in previous message, but I'll do it later tonight.

[NotMyFault]

The discussion seems a waste of time. What do you want to achieve? Probably the CRB is not the right tool. If you can explain what you want we can show a way how to achieve it (with other tools).

It will help if you try  to understand a little bit of color theory first, specifically RGB and HSL color models.

unfortunately the term „color“ is used with different interpretations in Affinity.

Color can be expressed in RGB or HSL, and you will find the conversion formulas. It seems you want to replace one color by another. But the image contains many pixels in many different colors. CRB affects the HUE component of colors only. All you posts seem you think CRB affects HSL. This is not the case.

e.g. if you try to darken orange you will get brown. 
Green is is most bright color (vs. Red or blue). Whenever you change the hue only, a. Bright green becomes much darker in red or especially blue.

This is just the mathematics behind the scene.

When you want to replace the green in the image against e.g. a light orange, the CRB cannot achieve this as it will create a dark brown tone. You must add an HSL adjustment or similar to adjust the lightness (which the CRB will never affect).

[Old Bruce]

The biggest problem with the Colour Replacement Brush is the first word in its name. It is a Hue Replacement Brush.

[SolihullRog]

I'm grateful for your contributions and they have been a great help.  It's a shame that you couldn't answer my simple question.

I am aware of the connotations of the term "Hue Replacement Brush", and might be persuaded by that term if it appeared to correctly describe the effects of the tool, and/or that was made clear in the documentation.  It appears not.

In particular, nothing convinces me that brown is simply 'dark yellow'. (I understand the maths).

As someone who is vastly experienced in all computer matters I am keen to keep up with the trends.

And as a previous keen user of Serif products and many other associated products, (including Photoshop, Photodirector, Paint.net, Coreldraw, Gimp, Paint, etc, etc) I am impressed by Affinity's range of functionality.  Unfortunately I am confused by its apparent poor code quality and/or documentation.  I am struggling to determine whether it has a future or not.

I'm afraid that this conversation has persuaded me in the wrong direction.

But thanks for your help and I hope that Serif are watching.

[NotMyFault]

7 hours ago, SolihullRog said:

In particular, nothing convinces me that brown is simply 'dark yellow'. (I understand the maths).

 

this sounds more like a strong statement of your believes and not like a question and openness to discussions.

[NotMyFault]

Maybe this can help.

One detail I forgot to mention is that CRB uses the HCL mode (not HSL) which may explain some of the confusion.

 

[SolihullRog]

Posted in error

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Please see attachment

 

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