Marshallarts tutorials
Digital Watercolour effects on SketchUp images
 
PLEASE NOTE:

This tutorial is currently being rewritten, this is a very rough version and much needs to be added and developed. I'll be including a layered .PSD file (so it's possible to follow along) and illustrating it with shots of what the results of each step should look like. For now there are no pictures and it is pretty disjointed, it will get better, I'm working on it as time permits. I thank you for your patience.

Grant Marshall


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There are many ways to apply interesting graphic effects to an image exported from SketchUp to add visual interest and give it a less mechanical look. If this is your aim, then there are no rules as such, provided the end product looks nice. This tutorial assumes that your aim is more specific, namely to simulate a traditional watercolour rendering without actually transferring the SketchUp linework onto paper to paint it with real watercolours. This is perhaps more challenging because your technique now has to fool the viewer into thinking he or she is looking at a watercolour. I believe that there are fairly clear rules governing what will look convincing and support the illusion and what will look fake or odd.

Why try to simulate a watercolour at all? Several reasons. Firstly it allows one to take what is essentially a collage of disparate elements from different sources (SketchUp models, photographic and hand painted entourage and backgrounds etc) and tie them together into a cohesive whole without inventing a new graphic for doing that.
Secondly it has an inherent 'looseness' which lends itself to presenting projects where the architectural details are not yet fully resolved.
But perhaps most importantly, it's a well-established visual language, for the viewer it has a familiar and pleasing look and feel. I believe that once the image has been passed off as a good watercolour the medium itself won't attract undue scrutiny. This means the image is better able to do its job which is to showcase the architecture.

I didn't invent the filtering methods used here, I only adapted principles described in a great photo-editing tutorial by Kaburaya. The method appears complicated because there are a number of 'features' of watercolour that need to be simulated and no single filter will do them all convincingly.

This was written primarily for Corel Painter IX.5 for Windows, the method for Photoshop (or Photoshop Elements) is sometimes slightly different so I'll cover any important differences at the end of each step. I am not familiar with the toolsets in Painter Essentials or Paint shop Pro but I assume it can be done in those applications, perhaps with some adjustments. Several steps involve 3rd-party plug-in filters, if you're on a Mac you might have to find suitable equivalents. Central to this method are the Kai Power Tools KPT Pyramid Paint filter and a watercolour paper texture, both of which are included in Painter IX.5. I feel it is worth buying Painter just for these things, even if you are more comfortable doing most of the work in Photoshop.

Clearly, it would be too cumbersome for me to describe all the possible ways to do something in every program you might be using and for all levels of user. Instead I'll focus on the aim of each step and you can use the method that suits your level of proficiency with the tools you have available. For example, where I suggest that you erase portions of a layer you might prefer to paint on a transparency adjustment layer instead.

If you do a lot of this type of work it is certainly worth learning more about layers, blending modes, layer grouping, adjustment layers, masks and channels and how they can streamline your workflow. In particular you should look for non-destructive methods which will allow you to re-visit earlier steps and adjust the effects of that particular step.

Filters generally can't be reversed, so I tend to duplicate a layer before applying a filter, ending up with quite large layer stacks. Where a filtering step requires a flattened image it is better to work on a flattened copy of the image brought back in as a layer (rather than irreversibly flattening your image). In Painter you can "Clone image" to save out a flattened version, in Photoshop "save for web" (jpg, quality 100%) does a similar thing and doesn't affect quality much. You can also do this by flattening the image, copying the result to clipboard (Crtl-A, Ctrl-C), then undoing the flattening step and pasting (Ctrl-V).


AIM

Traditional watercolour has some identifying features which give it its characteristic look. We'll need to recreate some of them in our faux version:

BRUSHMARKS The addition of brushmarks to break up SketchUp's smooth, flat areas of colour is perhaps the most obvious step and the easiest place to impart your personal style, but it is difficult to do it convincingly.

Obviously the character of brushstrokes varies enormously from artist to artist, but it's worth remembering that watercolours are typically applied quite wet with soft brushes, so dry, streaky marks made with a bristly brush tend to be the exception rather than the rule. The behaviour of the water itself tends to influence the look of the finished image at least as much as the brush does. A watercolour painting is really just a collection of different puddles, with it's character coming from the shapes of the puddles and what goes on within them. If the paper was wet with clean water before the paint was applied you'll hardly see any brushstrokes at all. Brushstrokes tend to be quite subtle unless the artist specifically indended to express the individual strokes, perhaps to define the direction of a surface or to create a focal point.

Generally, bold brushmarks will give your image the appearance of a loose watercolour sketch, while less obvious brushmarks are more appropriate for a more subtle, restrained render. Either way it's a good idea to relate their direction to the surface that particular colour is filling.

WHITE PAPER Watercolour artists often don't cover all the paper with paint. White paper can be an important part of the composition and help give life to the image. If your SketchUp images are edge-to-edge colour you'll have missed out on one of the easier 'tricks' and you can run the risk of the end result looking overworked and muddy. Generally speaking, larger areas of white will give the image a quick, sketchy, suggestive feel, while less white might be appropriate if you are simulating a more detailed, more 'finished' painting.

VARIABILITY (or non-uniformity or whatever you want to call it). It is very difficult to apply watercolour paint absolutely evenly, so as a result any patch of colour usually contains tonal variations caused by more or less paint or more or less water. In addition, the painter's palette is usually fairly limited, every colour in the painting is mixed from a few basics. Areas of colour typically have hue/colour variations caused by the incomplete mixing of colours on the palette, by brushes contaminated with other colours, or even by the artist deliberately blending different colours directly on the paper. It's also worth noting that watercolourists don't often paint with pure black or grey, neutrals are mixed from colours and usually have a colour tint. SketchUp produces unnaturally flat, even tones and colours on faces so we'll have to introduce value and colour variations.

WATER Water affects the behaviour of the paint and leaves tell-tale signs, the 'happy accidents' which give watercolour its charm. Painting on dry paper or over dried paint has a particular look, painting on wet paper or across wet colours has another. As the water flows on the paper it settles and dries and affects the paint suspended in it, leading to darker concentrations in hollows and at outer edges. We need to introduce these things into the SketchUp image.

GRAIN The graininess in a typical watercolour comes from 3 sources: Firstly the bumpy paper texture catches the light and forms shadows (most visible in white areas) - most image editing software simulates this with a screen of little grey blobs over the whole image, but it can easily look fake and I personally don't like it much. If you look through a book of watercolour paintings you probably won't see much evidence of it because the reproduction process usually seeks to avoid shadows on the original. Secondly those same bumps in the paper cause the paint to form tiny puddles of denser colour in the hollows. It's a different look and simulating it successfully is crucial to a convincing watercolour. And thirdly the pigments in the paint itself sometimes form a gritty sediment as certain colours react with each other when mixed. This effect is generally quite subtle and localized and probably not worth bothering with.

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There are many filters which claim to create a watercolour effect but in my opinion they all fail to give convincing results because they hope to achieve all the above characteristics in a single pass. Instead, this method works in steps, each building on the results of the one before and allowing adjustments at many stages.

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METHOD

STEP __ EXPORTING

Be sure to save the camera and sun position of your chosen view in SketchUp (using Pages). This will make it possible to make changes to the model in the future, re-export images and integrate them into your photoshop layer stack without too much trouble.

I typically work 4500 pixels wide and about 3200 high, bear in mind that many effects like blur amount and filter strengths are related to pixels, a smaller image will need lower values to achieve the same look. Larger image sizes may cause memory errors with some filters.

Choose the sun position very carefully, it determines the distribution of light and dark areas and this has a huge impact on the composition of the finished image. If necessary ignore the true orientation of the building (northpoint), rather adjust the sun to yield best shadows you can for a pleasing composition, at the same time 'explaining' the form of the building as much as possible.

You'll need to start with a minimum of 2 images exported from SketchUp:

* Linework only (textures OFF, colours OFF and shadows OFF). * Colours and shadows (edges OFF). Note that Textures can cause problems in Photoshop (visible pattern repeats and Moire pattern effects), it may be better to have them turned off or at least export an additional layer with them turned off.

A refinement would be to export separate colour and shadow layers as this allows easier manipulation of the shadow colour and density. I don't often bother, but if you want to try it set both the 'frontface' and 'backface' colours in SketchUp to white and export with shadows ON and edges OFF.

I typically export an additional image with only flat colours on, (edges OFF, transparency OFF, textures OFF, no gradients in background sky or ground). This layer goes down near the bottom of the stack and won't be visible in the final image, but it is very useful for selection masking. Use the magic wand tool to quickly select a material on this layer (even 'busy' materials like stonework or roofing), then switch to your working layer and work within the selection. If shadows are on in this image it allows shadow areas to be selected too. This becomes more useful later in the process when you have introduced tonal and colour variation into your main image layer and the wand tool doesn't really work anymore, it will still work on this layer.

Some thoughts on linework: You have 3 choices with linework: to omit it altogether to treat it as ruled lines, either ink or pencil to treat it as freehand lines, either ink or pencil

Processing the linework to make it look like freehand ink or pencil lines is a whole exercise in itself,
it is possible to apply 'ripple' type filters to the layer but because the filter is applied indiscriminately the results can look artificial.
Issues with parallel lines
turbulence eg.
*More to come here*>>>

so for now let's just pretend we are colouring up a neatly ruled pencil drawing.


STEP 1.

Add the linework to the colour image.

In Painter or Photoshop, copy and paste the Line image into the Colour image. It will form a new line layer on top of the colour image, obscuring it. Change the /composite mode/ (or blending mode) of the new linework layer from "Default" (or "normal") to "Multiply" and the white areas will appear transparent.

Linework exported from SketchUp typically shows 'jaggies' or a stairstepping effect on diagonal edges, most noticable on smaller images. At 4500 pixels wide it is less of a problem but I apply a very small amount of gaussian blur to this layer anyway, it gets rid of any pixelated look and helps it to sit 'in' the image rather than 'on' it. Alternatively, the linework can be exported much larger than we need it and then downsampled in order to smooth the lines, note that this will also make them look thinner.

I usually set the opacity to about 80% for ink in the final (lower for pencil), for now you can hide it so you can see the boundaries between colours. It's a good idea to lock this layer so you don't accidentally modify it. It's also good to get into the habit of naming your layers appropriately. Keeping things well organized can save you time in the long run, particularly as the layer stack grows.

STEP __ Paint pockets layer

Now we need to simulate the way the paint collects in the depressions in the paper and gives it a grainy look. This should not be confused with the way light falling on the paper accentuates the paper's bumpiness - simulating that is what the "apply paper texture" button does in most software, basically by adding a screen of grey blobs (typically in multiply mode) to the image. If you haze your eyes that "paper texture" tends to give the image an overall grey cast.

Instead we will use a layer set to "overlay" blending mode (we'll call it the /PaintPockets/ layer). With the Base layer active, create a new layer (it should appear in the layer list between the Base layer and the linework layer) and change the composite mode (or blending mode) of the new PaintPockets layer from "Default" to "Overlay".

I like to have this layer in place and visible right from the start because get a better idea of how the finished image will look and adjusting the other steps is easier. If you do that, just remember to hide it (and the linework layer) before running filters like Pyramid Paint and Beyond Edger on the image.

[Image]

Here's a comparison: A scan of a real watercolour showing the paint pockets, our faked Painter version which is pretty close, and the 'bumpy paper' look which you can see is a completely different look.

*Painter* users: Fill the new layer with White. Your colours will appear really bleached out, we'll fix that in a moment. Now choose a paper texture from the dropdown paper selector list. (Go to Window>library palettes>Show Papers if you don't have it on your screen). I use Italian watercolour paper because the look is pretty similar to the papers I use for real paintings, but there are other nice ones included. There are 3 sliders and an 'invert' button which will affect the look of the paper, and the distribution of our little puddles of paint will be based on that. The scale depends on output size - it has to look right at the finished print size. For this exercise we can use Scale 100%, Contrast 100%, Brightness 100%.

Now with your PaintPockets layer active, go to menu>Effects>Surface Control>Express Texture, Grain = 76% Contrast = 76%. Adjust the grey threshold slider in order to get the overall tonal value of the image back to about the same as before, mine was about 160. You can adjust these three sliders and the sliders on the Papers Palette and toggle the invert button there until you get an effect that looks /exactly/ like paint that has collected into darker pockets. I find the Invert button is the key here. Get a book on watercolours if you're not sure what the effect really looks like. Actually, get a book on watercolours anyway, it can't hurt.

*Photoshop* users: Fill your new PaintPockets layer with 50% grey (that means saturation = 0, Brightness/Value = 50 or if you're using RGB it'll be 128,128,128). Because the layer is in 'Overlay' mode, 50% grey has absolutely no effect on your image, that's a feature of the way overlay mode works and it's a useful thing to remember.

Now go to Menu>Filter>Texture>Texturizer, pick "Sandstone" from the texture list, scaling = 200%, relief = 4, light direction = Top, and check the 'invert' box. Hit OK. We set a higher relief value than we needed so now adjust the transparency of that layer to make the paint pockets look right, mine is at about 40%. Not as pretty as Painter's result, but it'll do.

Or noise layer
*More to come here*>>>


The sandstone texture is actually too small for this and the problem gets worse on larger images, it looks more like textured white 'Fablon' than watercolour paper (remember Fablon?). You can try selecting the PaintPockets layer and enlarging the whole thing 200%. Go to Menu>Edit>Transform>Scale, You'll probably need to zoom right out to see the scaling grips on the corners. Drag it larger and then zoom in to see the result. Click on the checkmark at top right if you're happy or on the cancel 'X' if you're not.


Once you have set this layer up in Painter it makes sense to copy it to an empty PSD file which can be used as a template file for starting new images in either Photoshop or Painter. Do this for different sized images and you have one less step to do on the next image. Or if you're comfortable setting up automated actions this would be a good step to automate.

STEP __ Adding variations to tones and colours

*More to come here*>>>

Now we need to make it look as though the areas of colour were put there with a brush

another way is to paint on a layer set to overlay or multiply blending mode

overlay a layer is set to Overlay and filled with 50% grey (RGB value 128, 128, 128) it will have no effect at all on the underlying image.

there's no need to add the grey, you can use a transparent layer. anything lighter will lighten the underlying image anything darker will darken it So if you put the colour selector somewhere on the horizontal mid line of the colour triangle (in other words value = 50%) (dead in the center is good), colours can be added with gentle puffs of an airbrush tool without lightening or darkening your image (which would look strange). similarly if you use just greys you can lighten and darken as though you were adding or removing paint. Why use an overlay layer for this? because if you paint directly on the base image layer it will darken it and it'll go outside the lines and colour white areas too. Using the grey overlay layer means it just changes the hue of the paint that's on there, nothing more. It'll also have more effect on denser paint.

*More to come here*>>>

At this point you have the option of doing some gentle erasing (either directly or using masking layers) to introduce value variation into the areas of colour so as to break up the very flat, uniform look. Select a colour with the Magic wand tool (sensitivity about 5) and erase within that colour selection with a big eraser (opacity about 5%) so as to lighten some areas just a little.

Try both soft and hard-edged erasers in varying sizes and brush shapes to avoid a repetitive, mechanical look. Remember, this aims to simulate brush strokes, so the direction and length of the strokes should be related to the colour you were "applying" and the direction should also follow the particular surface you are painting. It makes absolutely no sense to have a single "brushstroke" starting in the sky, crossing through the roof colour and the wall colour and finishing in the lawn. In a real painting your brushmarks would be confined to one colour zone at a time, so use that Magic wand tool and then work within the colour selection.

It is better to add these brush strokes and tonal variations now and they'll be processed along with everything when you run the filters. If you wait until after the filters before adding the brushmarks they won't look as real.

the filter really pulls it all together into a cohesive whole
the more you do before filtering, the better the outcome

windows dab them with an eraser lighten the top half of the window - generally it is reflecting sky. That's a rule to be broken if it doesn't look right in particular situations like under deep roof overhangs.

Experience will tell you how much is enough and what effect it will have down the line, so for now let's leave things as they are and move on.

Alternative method:

Using a global immumination (GI) render instead of (or along with) the SketchUp colours and textures image

Ambient Occlusion Render
Camera alignment
Shadow colour
Sun Colour
Reflections- water and glass

*More to come here*>>>


With the variations taken care of, we also need to recreate the effect of someone trying to stay inside the lines with a brush

STEP __ SIMPLIFY FILTER

You'll need a simplifying filter which will slightly round the corners as though the brush couldn't quite get in there. Painter IX has the *Pyramid Paint* filter in the KPT Collection, its job is to simplify photographs, dumbing down detail into simpler areas of colour but it does an excellent job softening SketchUp's colour output.

I'm sure there are other similar "Simplify" filters out there which will work, the BuZZ.Simplifier filter from fo2pix looks promising but I haven't done any serious testing with it yet. ***(To do)

Because most filters run their effects calculations on a certain radius of pixels, at larger image sizes the effects become proportionally smaller, so you'll need to increase the 'effect' slider to see the result you want.

At 4500 pixels wide you may need to run this filter twice at maximum to really loosen things up. Or it might be better to work on the colour layer at reduced size to get bold results from the filters, then enlarging again before combining it with the linework layer. Since global filters seldom do exactly what I want across the entire image, I usually duplicate the layer, then run the effect filter at different strengths on different copies of the layer, placing the wildest version uppermost. Then I just erase any areas where the effect looks excessive, revealing the milder effect layer underneath, merging the 2 layers when I'm done. This is particularly useful when I am integrating a background or foreground photo into the image and I need very high settings on the photo and lower settings on detailed parts of the building.

*Painter* users: Go to Menu>Effects>KPT Collection>KPT Pyramid Paint

The ludicrous interface will be familiar if you've used Bryce, it's more like a puzzle than a tool. You can enlarge the preview, force the control palette to stay open, save your workspace layout preferences and your filter settings to the 'memory' buttons palettes and save the settings permanently to a settings file. I'll leave you to figure out how to do those things.

Our sample image is quite small (900 pixels wide), so set the detail value slider quite low, at higher values there'll be more bleeding between colours, particularly in narrow areas. That'll work well for a very quick, rough sketchy look, but perhaps not for a carefully executed rendering.

I increased the saturation because the SU image was pretty lifelesss, I increased the contrast and brightness so that whites bleach out, and I increased Blue so that SketchUp's grey shadows go slightly blue. I never use black paint in real watercolours, so my greys are never completely neutral, usually they are slightly blue or purplish.

Here are the settings I used for this image and the preview:

You can see how this step has removed detail from the image, blurred a few edges and also killed off the textures (which I feel is a good thing, but more about that later).

*Photoshop* users will take a few steps to achieve the same thing because Photoshop's 'artistic>watercolor' filter does the simplifying thing well enough but it adds in a nasty, gloomy darkening effect which we need to counteract.

First we need to work on a copy of that base layer. Right-click the base layer in the layer palette and duplicate it. With the new layer active, go to Menu>Filter>Artistic>Watercolor

Set Brush Detail = *5* or *6*, Shadow Intensity = *0*, Texture = *1*, then hit OK

See how it adds patches of pure black to the edges? Those will cause major problems when later steps act upon them, so we really need to get rid of them.

Go to Menu>Image>Adjust>Selective Color, pick 'black' from the dropdown list and pull the black slider all the way to the left.

Now change the /blending mode /of the layer to "Overlay" and then go to Menu>Layer>Merge down to combine the layers.

It still looks a bit gloomy for a watercolour, so go to Menu>Image>Adjust>Hue/Saturation and increase saturation about +20. That helps, but the greys are still rather lifeless, so go to Menu>Image>Adjust>Selective Color, pick 'neutrals' from the dropdown list and push the Magenta up +3 and the Yellow down -6.

The result should look something like this, and be fairly close to what the Pyramid paint filter reached in one step. One big difference is that the Photoshop method didn't introduce any blurry 'runs' like the KPT Pyramid Paint method did. You could easily add some here and there with a few dabs of Photoshop's 'Blur' tool.

[Alternative:
For photoshop users: If you don't have KPT Pyramid Painter plugin filter you'll need to do that step differently. First increase Image>Adjust>Hue/Saturation Saturation = +50 Lightness = +20 Duplicate layer, change new layer to Overlay

Use Photoshop's Artistic>Watercolour filter. Brush Detail = 13 Shadow Intensity = 0 Texture = 1 Unfortunately, even with Shadow Intensity at zero it still introduces a lot of black which doesn't look anything like a real watercolour Overlay gets rid of the black. Another method would be to select the black with the magic wand selector (sensitivity about 30, non-contiguous) and then increase the brightness up to pale grey or white.]

*More to come here*>>>


Some thoughts about material textures:
Textured materials like rooftiles and brickwork can present a problem because they are usually repeated tiling patterns. When these go through the watercolour filtering process the pattern repeats tend to become very obvious and unsightly. Even if this doesn't happen, the result is often too regular and perfect, not somerthing you'd expect to see in a real watercolour.

There are a few ways around this problem

*More to come here*>>>

clone brush
disturb the regular pattern before filtering textures off layer under
erase through
Multiple filter passes

STEP __ TOUCHING UP

repair gradients
smart blur filter
Painter Blender stump
blender smudge without streaks
*More to come here*>>>

Restoring detail

STEP __ BLEED.

This step will soften the image slightly and add a bit of variety to what's happening along the edges of the colour fields. I find I often skip this step, it needs to be quite subtle or limited to just a few areas. Too much of it over the entire image can give the impression that the painting was done on unsized paper.

Again, it might be a good idea to duplicate your layer before running this step on it. Run the filter on the upper copy, then simply erase any parts which look excessive, exposing the unaffected layer below. Merge both layers when you're done.

For this you will need the "PaintEngine" <http://www.fantasticmachines.com/demo_downloads.htm> filter, free from *Fantastic Machines*. When installing it remember to place the accompanying .ini file into your main Windows folder because it contains all the great presets, including the one we need.

Now go to Menu>Effects>Fantastic Machines>PaintEngine. Pick the '/mass poster/' preset, it's not perfect as is, but the settings are a good starting point.

Combined with the previous step, it does a great job of leaving some edges sharp (simulating painting wet-on-dry) and blurring others allowing colours to bleed together (simulating wet-on-wet). The default "Effect>Amount" value of 2.92 is too high, particularly for this small image, so try 1.0, and also change both the "Brush>Lighten" sliders to 0.1 (one of them is currently a negative value which will cause ugly greying of all the whites in the image).

Save the adjusted preset as something like @Watercolour so it'll be at the top of the list next time.

STEP __ EDGE ACCENTS

Now we want to darken the edges of colour fields to simulate the effect of the colour wicking out to the edges of brushstrokes as it dries. For this you'll need the "BeyondEdger4 <http://www.bmath.net/dc/ind.htm>" filter from *DC Plugin Filters*, also free, available on its own or as part of a set.

Go to Menu>Effects>DCspecial>BeyondEdger4

Go with the default value of 10 and leave the 'Use color' box unchecked, this appears to increase the density of the field's own colour at the edges rather than just adding black as many 'watercolour' filters seem to do. Don't overdo this effect or it might overwhelm delicate linework. At very high settings on large images it will create a sort of 'grain' effect everywhere that doesn't look anything like watercolour, so avoid it.

Here's a before, after (Painter) and after (Photoshop). The effect is subtle, but remember that we are simulating a fairly careful painting here as opposed to a watercolour sketch. This filter interacts with the previous one to give a really interesting edge, up close it really looks as though water, pigment and paper fibers worked together to cause it.

STEP __

Backgrounds, foregrounds - adding, processing
*More to come here*>>>
importing scanned strokes


STEP __

Adding and processing entourage (people, cars and plants)

*More to come here*>>>
Using SketchUp Models
Using Photos
Using Entourage Arts cutouts
Hand painting


STEP __

Apply paper texture
Optional - omit?

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