problem with brush sizes

Hi, im very new to the rebelle, so maybe this is more question than bug - i was trying to start new canvas, 300 DPI A3 (same problem with A4/600dpi)  - by pixels, its large. I have problem with the brushes - even size of 100 is terribly small - what am i doing wrong? or, is there way to define the brushes in mm ? Or, am i looking on it with wrong perspective, and is there other way to lay large areas of water colors ?

Thank you for answer.

You may find that this brush tutorial series helps  - https://www.youtube.com/playlist?list=PLUuRcU19WlxYuIav5Pf7OecQtzSfyOwrS

I have found that the most I can do is 300 at A4 size due to the limitations of my laptop, if I try and do A3 or 600 dpi becomes very slow.   My plan is, when I get around to printing larger sizes, is to enlarge them in Photoshop.  The largest I have printed so far is A4 and am happy with that so I hope the larger sizes also print well as I am planning an A2 soon .

To print large areas of watercolour I wet the canvas, pause the diffuser, paint and then turn on diffuser and go and do something else for between 5 and 30 minutes while it works.  Try experimenting with a very small canvas till you get the effect you want and then do it on your working size to save time.  Those with more powerful machines/set ups will have different experiences to me.  As you will see from my portfolio I am still very much experimenting about both Rebelle and Art and do not have a particular style unlike many of the experienced artists here.

Grapher:

You aren't doing anyting wrong.

If you play around with dpi settings (with the brush set to maximum width,) you'll note that at 72dpi the brush is very large and covers quite a bit of canvas. As you progress through dpi settings, you'll note when you finally arrive at 600dpi that same maximum width brush will be a small circle on your paper.

That said, only a programmer from Rebelle can tell you the reason why. I suspect much of it has to do with the fact that the CPU would choke if it were forced to calculate the flow of paint, if the brush were the same size on 600 dpi canvas as it is on a 72 dpi canvas. 

Hi @grapher,

thank you for posting this question. It's just like @csandnes says - we are limited by the CPU power of today's computers. Rebelle is very much compute-intensive at the moment due to the simulation of fluid flow because the math running behind Rebelle is quite complicated. Rebelle itself is different from standard paint programs, it has to compute around 25 layers, which include water simulation, diffusion, wetting, drying and all water effects.
This is closely related to the size of the brush as well. If the brush was larger at this stage, it would significantly influence the simulation speed and the application would lag more.

We have already enlarged the brush size from the first version and understand the need for bigger brushes, that's why we will continue optimizing Rebelle and its brushes even more for higher resolutions.
We'd also like to implement a watercolor "Fill" feature into the future versions of Rebelle for laying large areas of watercolor on the canvas.

Veronika,

I'm curious. Are all brush/flow calculations performed simultaneously? If yes, I wonder about the possibility of treating a large brush as if it were a progressive JPG in nature.

As you are aware, with a progressive JPG the first layer of data presents as a blury image. The next layer adds more clarity until the final layer, which completes the image. So, If a large brush size is selected  (say, any size above the size Rebelle is currently programmed for) perhaps Rebelle could treat it the same as a  progressive JPG.

In concept the user could lay in a large swath of color, via a non-intensive algorithm, allowing the user to see areas of the canvas he/she blocked in.

If the user likes the inital wash, perhaps a button is selected to complete the flow process.

If a button approach is not practical, perhaps the process is automatic but with continued successive layers until completed.

I realize there is no getting around choking the processor but for those who have patience, the user would at least be able to lay in large areas of paint then wait until the processor finished the job, one layer at a time.....or some variation of the same to complete the task.

Such limitation of brush size make the app practically useless to me.

Interesting -first few hours using this software on a xp Pen 15.6 tablet - i find the brush size challenge to almost emulate some of the core restictions in the actual media - in an abstrat way -  there are ways around it - by reducing banding of washes with opacity and blending - also the actual use of water and flow - as long as you don't start your laptop on fire  and do things slowly it will create good results to overcome the larege flat wash conundrum. Experiment p just the way you would in the actual medium. I think it is a fantastic peice of code thus far - but like i said I am only one illustration ir (book illustration) importing real watercolour sketches and tweaking-building on them.

After about 40 minutes i found ways around the brush size challenge - but it is all subjective and relative to your process. You need to adapt to the software and bring your own experiece of the actual meduim into it - it won't ever be a perfect transition - Have fun with it.

It’s a very frustrating problem. I work on more than A4 size line scanned drawings and it’s impossible to put a background with a large brush like in real watercolor painting.

Hi @lian00,

we're optimizing Rebelle right now and we hope the optimizations will enable us to enlarge the brush. We'll see how the development goes. In regards to the Fill tool, a basic fill will be implemented in the future version.