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I don't know if this is specific to Krita, I'd just like to understand how to handle it, as I cannot find any specific posts or info addressing it. [Please note that I am a beginner and I am not doing this professionally].
If anyone could please advise, it would be greatly appreciated.

If you're working with 'physical' painting/drawing tools, you know the size of your canvas or sheet, and the size of your brush tips, pens, etc., like '2 in brush', '1/2 in brush', etc. (see Bob Ross' 'The Joy of Painting' videos, for instance).
That tells you immediately what size, relative to your canvas, your brush stroke will have when you apply it.
If your canvas is 10 in wide, and you use a 2 in brush, you know your brush stroke will occupy about 1/5 of your canvas' width.

In Krita, when I create a new file, I set the canvas size in cm (e.g. 5 x 5), and I need to set the resolution (e.g. 300, 600 ppi).
Given that brush sizes are expressed in pixels, not inches or cm, this implies that the same brush, set to the same pixel size, on a canvas of the same size , will appear exactly twice as large if the ppi setting is halved.

I understand the technical reasons for it, but I do not know how to handle it, for consistency.
Of course I can resize the brush tip according to the resolution, so that the size of the brush stroke is the same, but as you know that completely changes its appearance, because (at least for the brushes I am using) the brush tip is an image of fixed size.

I pasted two examples below.
I made a screenshot after resizing both canvases to 'fit height', to show the alteration in the definition.
The 50 pixels brush stroke takes exactly twice the relative width of the canvas in the 300 ppi one compared to the 600 ppi one.
Resizing the brush to 25 pixels in the 300 ppi canvas does make it scale to the relative size it has on the 600 ppi one, but you can clearly see the loss in definition and detail.

One obvious solution would be to stick to the same resolution in all files.

Is that what you would advise to do? Any other ideas?

Thanks!

enter image description here

enter image description here

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  • Hi. Welcome to GDSE. More PPI means the image is larger in pixels, but the brush doesn't get bigger unless you resize it manually. Brushes are also made of pixels. Pixel size = size in inches x ppi. So, what you are describing is exactly what is expected. There's nothing wrong here.
    – Billy Kerr
    Feb 6, 2021 at 11:03
  • Thank you; so I guess the only solution is to think of a digital canvas size in pixels rather than in cm. If I paint on a 600 ppi 5 x 5 in (= 3000 x 3000 pixels) canvas, a 50 pixels brush stroke will occupy 50/3000 = 1.67 % of the canvas width, corresponding to 0.083 in. If I want the same brush stroke to preserve its absolute size (and details) on a 2.5 x 2.5 in canvas, i.e. for it to occupy still 0.083 in, which is now about 3.3% of the canvas width, the only solution is to use the same 600 ppi resolution for the smaller canvas. At least, that's what I am getting from this discussion.
    – user6376297
    Feb 6, 2021 at 11:55
  • That should also imply that, if I do not want to keep resizing my brushes, and instead I want to use them as if they were 'real' brushes with a fixed absolute size, I can only do that by sticking to the same resolution in ppi for all my canvases. From some tutorials I gather 600 ppi is an OK setting for work that is only viewed on computer screens (is it ?). BTW, that particular brush I tried before, when it's set to size 50 pixels, occupies about twice the expected width, whereas another standard Krita brush, also set to 50 pixels, occupies the expected 0.083 in. Not easy... :S
    – user6376297
    Feb 6, 2021 at 12:01
  • Raster images have a dimension measured in pixels, not in physical dimensions. For on-screen images in browsers/on the web, the PPI setting is irrelevant. The number of pixels is all that matters. PPI (sometimes called DPI) is just a conversion factor used in printing. 600ppi is excessive for print. 300ppi is the usual setting. If you don't understand PPI/DPI , read this: The Myth of DPI.
    – Billy Kerr
    Feb 6, 2021 at 12:08
  • as a side note, Krita now supports scripting so if you feel fancy you can just make yourself a script that'd modify brush size depending on your DPI settings
    – Sergey Kritskiy
    Feb 6, 2021 at 15:27

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  • 50 pixels is 1/12 of 600 pixels, so in 600 ppi (pixel per inch) it is 1/12 of inch.
  • 50 pixels is 1/6   of 300 pixels, so in 300 ppi (pixel per inch) it is 1/6   of inch.

                                      1/6 of inch is twice as wide as 1/12 of inch.

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