Painting Tools - Brush Up Your Brushes

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Master your bitmap brush tools

Tom Arah investigates how you can take control of your photo-editing and painting brushes.

Take control of your bitmap brushes

Simplicity Itself?

It's pretty self-evident that you can't paint without a brush, but because the brush tool is so central to bitmap editing it's easy to take it for granted. To gain real control of your painting and photo-editing, however, you need to master your brushes and to do that you need to understand them.

One of the reasons that the brush is so under-appreciated is that its core job is so simple. Most users' first experience of bitmap editing is with the Paint program that comes bundled with Windows. Drag a path on screen and all the underlying pixels are converted to the current paint colour - that's all there is to it. In fact Paint provides twelve brushes to choose from with three sizes of circular, square and left and right angled lines. Selecting a square brush simply produces square ends to the stroke, but much more interesting are the angled lines which produce calligraphic effects with the width of stroke depending on the angle of the brush. It's not exactly Picasso, but it shows how even a small change to your brush can have major consequences.

Top of the range?

Move on to market leader Photoshop and it's surprising just how similar the brush tools seem at first with the Pencil (n) tool in particular working exactly like Windows Paint's brush. When you try the Brush tool (b), however, the practical difference becomes apparent as the strokes instantly seems much smoother. Zooming in on a brush stroke reveals the secret - anti-aliasing. The pixels around the immediate edge of the stroke aren't solid but are a mixture of the brush colour and the underlying colour. By smoothing the edge, the pixelized effect on angled lines is removed and the lines look sharper and more natural.

As well as the benefits of anti-aliasing Photoshop's brush tool offers another new feature: soft grayscale brushes rather than solid black. Instead of applying colour solidly across the stroke these brushes produce more diffuse and subtle effects. The principle is the same as for anti-aliasing so that the semi-transparent effect is produced by mixing the values of the brush "blend" pixel and the underlying "base" pixel. The combination of anti-aliasing and transparency reaches its peak in the dedicated Airbrush tool (j) which adds a further trick by allowing the colour values to build up and spread just as they would with a real airbrush.

The importance of interaction

It's this interaction between the brush and the underlying pixels that sets Photoshop apart from Windows Paint and which leads directly to Photoshop's main distinguishing feature - its retouching brushes. These don't actually add colour at all but instead work mathematically on the pixel values already in the bitmap. The Dodge tool, for example, lightens each colour it passes over by moving its RGB values to the maximum 255 while the Burn tool darkens them by moving towards 0. The Sponge tool works by shifting each pixel's saturation value and the Sharpen and Blur tools work by increasing or decreasing the gap between adjoining pixel values. There's a big difference between the effects of the originating brushes and retouching tools but essentially they work in the same way by algorithmically changing the current pixel values.

The underlying maths in Photoshop's brush tools is certainly more sophisticated than in Windows Paint then, but what about the control offered over the brushes? Photoshop's Brush palette offers just 17 default brushes for each tool based on hard and soft variations ranging from 1 to 100 pixels in size. In another way Photoshop looks even more limited than Paint as all the brushes it offers are circular. Clearly there must be a way to customize the brushes provided, but Photoshop certainly doesn't make the capability obvious. As a result the vast majority of Photoshop users only ever use the completely inadequate defaults. The power does exist, however, but only for those prepared to look for it.

Taking control of Photoshop

The first port of call to take control over your Photoshop brushes is the Options palette which can be called up by double-clicking on the tool icon in the toolbox. This offers a range of settings many of which are to do with controlling the transparency of the stroke. The opacity/pressure setting is the most important and can be specified from 0% transparent to 100% solid. (This can also be changed using Photoshop 5's keyboard shortcut, Alt + numbers, so that Alt + 2,5 will set the current opacity or pressure to 25%.) Essentially the opacity effect works just like anti-aliasing and brush softness but is set for the stroke as a whole.

Changing opacity helps produce more subtle effects, with transparent strokes that both interact with the underlying image and build up to the solid colour as they overlap, but they still seem slightly artificial as the effect is uniform. A more natural effect like a brush drying out can be created by specifying a number of Fade steps. More importantly, for those with pressure-sensitive tablets, you can set the size, opacity and/or colour to vary depending on the pressure you apply. This works by bringing in another constantly changing variable into the maths that determines the current blend input and so the final result value. The interactive control enabled by pressure-sensitivity is crucial for advanced work especially when it comes to retouching where a light and interactively varying touch is essential.

Doing the maths

As well as its management of opacity, the Options palette offers control over another crucial parameter - the blend mode. There are up to 15 of these modes available in Photoshop ranging from Normal through to Luminosity and each has a radical effect on brush behaviour. Each blend mode works by affecting the maths that determines the final pixel value so that the Darken option, for example, will only change the final pixel's RGB values if they are darker than the current values while the Luminosity option will only affect the pixel's brightness. The control that blend modes offer is immense but be careful - remember to change the mode back to Normal once you're finished or results will be unpredictable to say the least.

The Options palette gives much finer control over the maths that determines the result colour, but it still hasn't given us basic control over the current brush. It's by no means obvious but in fact this is achieved simply by double-clicking on an existing brush icon or blank area of the Brush palette which calls up the Brush Options. At last with the dialog's Diameter option we can change the size of the brush and with the Angle and Roundness settings we can create square and calligraphic effects. With the Spacing option we can also produce completely new effects. By setting the spacing to over 100%, for example, the brush shapes laid out along the stroke no longer overlap so that you can create dotted and dashed lines.

Create your own

In fact Photoshop has another command hidden away that offers even more creative control. By marking off a rectangular area of a painting with the Marquee tool (m) you can then use the Brush palette's Define Brush command to create your own brush. By selecting a random grayscale pattern, for example, you can create a quite realistic charcoal-style effect. Once you've created your brushes you can save them to file and load them whenever you need them with the Brush Palette's Load Brushes command. Adobe has even provided three sets in its Goodies\Brushes directory to get you started.

Photoshop's control over its brushes is by no means amazing and Adobe seems to be trying to hide what customizing control it does offer, but if you look for it you can find some very useful capabilities. By selecting an object and turning it into a brush with a spacing of over 100%, for example, you are effectively creating a poor man's Image Hose tool for repeating elements throughout your image. Alternatively with an ordinary brush, selecting the Options palette's Wet Edges command has very interesting results. Essentially the anti-aliased edge of the stroke are left unchanged but the body of the stroke is made semi-transparent. This gives the effect of pigment diffusing to the edge of the stroke just as it does when painting with watercolours.

A dedicated solution

By exploring all the power on offer we've come a long way from Photoshop's default brushes, but it's also pretty clear that we're forcing Photoshop into areas for which it was never really intended. A completely different and completely brush-centred approach is taken by Metacreations Painter.. Each of its natural media brushes is designed to mimic a traditional artist's tool and the range on offer is amazing. The default brushes are divided into 15 categories ranging from charcoal through to watercolour with each category offering up to twenty options. All told there are well over a hundred radically different default brushes with hundreds more available for loading from provided libraries.

What makes the brushes stand out is their incredible realism. Just within the Brush category, for example, you could select three completely different options each of which a real artist would be likely to have on their palette. The "Big Loaded Oils" brush, for example, is built up of multiple bristles each of which lays down a slightly different colour just as it would if you had mixed it yourself. The "Brushy" brush, on the other hand, acts like a dry brush that soon deposits its own paint but then drags through the paint already on the picture. The "Sable Chisel Tip Water" works very differently again, this time not laying any colour down itself but acting as if we were brushing our image with water.

This artistic approach to brushes is worlds away from Paint and Photoshop and the creative freedom it opens up seems almost like magic. In the hands of a master, there's no question that Painter is far and away the most creative package around and capable of creating real works of art. The problem is that it's very difficult to become a master. The range and realism of the brushes is amazing but unless you already know the difference between your "digital sumi" and your "camel hair", you're more likely to feel intimidated than enlightened. Clearly we need to try and take control of Painter's brushes as we did with Photoshop's.

Mastering your palette

This time the first port of call is the Controls:Brush palette (Ctrl + 5) which offers three important sliding controls. The first controls the size of the brush from 1 to 750 pixels though this can also be set interactively by holding down Alt + Ctrl and dragging onscreen. The second controls opacity and so enables the creation of semi-transparent strokes where the underlying paint shows through. The final option, Grain, is completely new and adds texture to the stroke based on the current choice of paper in the Art Materials palette. Different brushes respond differently to the grain setting so that charcoals are affected whereas oils aren't. Even finer control comes with a pressure-sensitive tablet where light strokes will colour just the peaks of the grain whereas heavy strokes will fill the valleys.

The importance of paper grain is a major step forward in terms of creative realism compared to Photoshop's purely colour-based approach, but there is clearly a lot more that separates the two programs' brush handling. In fact the fundamental behaviour of Painter's brushes is controlled by two major options available if you extend its Brushes palette, namely the "method" and "subcategory". Each brush is based on one of seven main methods: Cover works by obscuring underlying colours, Buildup builds to black, Eraser lightens like a bleach, Drip distorts the underlying colours like a liquid, Cloning copies pixels from one area to another, Wet enables colors to flow and mix and Plug-in opens up a whole range of special effects.

Modes and subcategories

As well as its major method each brush has a subcategory. The majority of these determine the extent of anti-aliasing and whether the brush is affected by the paper grain so that, for example, the recipe for the various chalk and charcoal brushes is "Grainy Hard Cover." Sadly things get a lot more complicated with the Plug-in method as this offers no less than 28 options. Many of these such as "Hue Add" and "Val Add Sat Sub" work like Photoshop's blend modes, but others such as the "Confusion" subcategory defy description and demand experimentation. As it's possible to change both a brush's method and its subcategory the creative options are immense with the ability to create a multiple-bristle felt-tip or a chalk-based tool that adds confusion!

As well as being able to customize the central brush method - the maths that determines how the result pixel is calculated - we also need to be able to control the brush itself as this determines the blend input value. This is achieved through a range of separate palettes available from the Control menu of the Brush palette. The most important of these are the Sizing and Spacing controls which, like Photoshop's Brush Options dialog, offer control over the shape of the brush dabs and how these are distributed along the stroke. The control is similar to Photoshop's but it is much more comprehensive. It's possible, for example, to change the brush stroke type from single to multiple to rake, each of which is then controlled with its own dedicated palette. Every possible feature that could make the brush effect more realistic is catered for so that with the rake-based brushes, for example, you can control factors like the contact angle and even the amount of turn.

Just when you thought...

All told, with no less than seven palettes controlling every minute detail of brush behaviour, the options are frankly frightening. What's more, if you thought that you might finally be getting to grips with the huge range of variables, Painter introduces another crucial factor - variability. The Sliders palette allows eight factors - size, jitter, opacity, grain, colour, angle, resaturation and bleed to be tied in to constantly changing factors such as the pressure, direction and velocity of the brush. This ensures that every stroke will be slightly different not only to each other, but also across its length just as they would in real life.

After exploring and effectively reverse-engineering Painter's brushes it's a lot clearer how the program goes about achieving its results, and also how you can change major settings. On the other hand I don't think that more than a handful of users could really claim to feel totally in charge of their brushes. In many ways this is down to the sheer range of variables on offer each of which can have a profound effect on the brush behaviour. However it's also down to the program's unbelievably unhelpful terminology and interface that seem almost designed to prevent the user taking control. If any program is in need of a radical rationalization and simplification it is Painter.

Opposite poles?

Looking at the way Photoshop and Painter approach their tools has been like looking at two opposite poles. Photoshop seems determined to oversimplify its brushes to keep the program streamlined and efficient for its photo-editing duties. Painter on the other hand seems determined to make its brushes even more complex than they naturally have to be for their creative role. The impression is cultivated that the two programs are natural opposites and so natural partners - Adobe has even gone so far as to call Painter a "strategic partner" to Photoshop.

To an extent that's fine as each program should naturally play to its strengths. However, the fact remains that both programs are ignoring huge areas of functionality that their users would benefit from and, more to the point, they are ignoring it deliberately. Each program acts as if there is some fundamental barrier between editing and originating that prevents them offering any crossover functionality. As we've seen though that's just not the case. Painting and photo-editing are two sides of the same coin, just different approaches to manipulating the colour values on the bitmap grid. There are different variables involved and different levels of complexity but ultimately both painting and photo-editing come down to brush-based maths.

Rather than trying to avoid stepping on each others' toes both programs should be trying to fill each others' shoes. Photoshop can and should offer some of the artistic creativity of Painter, and Painter must offer more of the simplicity and efficiency of editing in Photoshop. More than this, both programs must put a lot more effort into making the control they offer accessible as efficient use of the brush-based tools is just too important to be left to the experts. In short, what's needed is brush-based power that is both comprehensive and comprehensible.

If Photoshop and Painter don't learn these lessons and continue to restrict their users while trying to maintain the artificial divide between origination and editing they will leave the way open for open crossover programs, such as Corel PhotoPaint, to fill the gap - perhaps permanently.

Tom Arah

February 1999

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