Tuesday Tutorial Re-boot: To line or not to line

11 05 2010

When starting a digital rendering, just like with a hand rendering, the first step is always to create the lines you are going to render within.  Generally people use lines directly taken from AutoCAD for digital renderings as these are the “cleanest” lines, and allow for some shortcuts such as exporting each area as its own file.

This method, which I have used often, involves turning every layer off except 2 – one framing the layout window, and one with a single rendered material (turf, pool edging, brick patio, etc.) You repeat this with every material, then bring them into Photoshop, and create a single drawing with the different areas as layers.  The advantage is that you then can use the magic wand to select even the most complex shape in a single click, regardless of how it will intersect other layers.

The end product is a clean rendering that has good line-weight, and reads easily.  The problem is you also have a drawing that has perfectly straight black lines, which add neither realism or soul to the rendering.

The second method is to forgo lines altogether.  Use the method described above, but turn all the cad layers off before saving (and make sure you selected both the area inside the lines, and the lines themselves to insure there are no gaps in your rendering).  This moves you a step more natural, as you have slightly blurred edges between materials, making a more aerial-photographic look to the rendering.  This may serve well in certain presentation settings (when trying to show the design blending in with existing conditions for instance), but the lack of hard lines, and of line-weight, greatly reduce the readability of the design.

In general, I prefer a third method that is less efficient, but gives – in my opinion – far better results than either of the other methods.  This involves printing out your full design, doing the line-work by hand, and then scanning it in to render from.  This involves a few levels of added difficulty, as to have a single person render they need to be equally skilled with Photoshop and a pen, a large-scale scanner is nearly a must, and there is another time-consuming step added to the process.   The added style, in terms of having a drawing that reads well AND has soul, more than outweighs the challenges in my book.

I said a large-scale scanner is nearly a must because it can be done with a traditional 8.5 x 11 scanner, but the line work must be far more precise, and line-weights are much harder to balance at a small-scale.  (I am using a small scanner for this project, and a .1 with a straightedge is significantly thinner than a .05 freehand drawing lines less than half an inch in length.)  Some of this may be due to the fact that I am slightly out of practice on my hand rendering, but some is also the difficulty of small-scale work.

One thing I like to do to simplify the process is to first draw the ground plane with just material borders, scan that, and then fill in any detail (line hatching for decks/paving if desired, or, in this drawing, the flagstones), and rescan the whole drawing.

This has two main advantages.  First, it allows you to still color as a block, and then add the detail later, when it doesn’t slow the rest of your work.  Second, it allows you to tweak the line-weight on those detail lines.  This may play a role even when working with a large format scanner, but it is a lifesaver when working small format.

This way you can, after cleaning up the scans and making the white areas transparent, you can delete the outer edges of the detailed scan’s lines, reducing the line-weight, and increasing readability.

One of the tricky parts of this process is how to make the black lines the only thing on a layer, so you can render behind it and have the black lines not edges with a light gray halo.  The first way you can do it is by selecting the white areas, deleting them, and darkening the other areas.  This can often lead to white/gray artifacts in the black lines.  The better way is to use masks/alpha layers.  First we have the scanned image:

The first thing that needs to be done is cleaning up the white areas.  The easiest way to do this, along with darkening the lines, is by increasing the contrast of the image.

Once you have a sharp black line on white, go to Image->adjustment->invert.  this will give you a negative image, with what was black white, and what was white black.  Then go to Image->Adjustment->Hue/Saturation and desaturate the image.

This step is necessary to make it into a masking layer, and it also allows you to more easily see areas where the black lines (now white) are slightly gray and transparent.  You can now tell if you need to up the contrast even more.  Then make an additional layer of solid black.  Open the masks window by going to Windows->Masks, and click on the icon for “Add a Pixel Mask”.

Select your inverted layer, Hit CTRL+A to select all, and CTRL+C to copy the image.  Then select your black layer that now has a masking image (Shown with a white box in the Layers palette).  The way to paste info into you mask layer is by clicking on the Channels tab of the layers palette.  At the bottom of the list you will see a layer that is not active and is pure white.  Turn on and select the layer, then hit CTRL+V to paste your image data.

By turning off the masking/alpha layer, you now have a layer that is pure black with transparency for your textures to shine through.

The only remaining thing is that if you do need to edit the layer, you don’t edit the black layer, you go into the channels, turn off the RGB layers, and turn on the masking layer.

Then you edit this layer.  So if you need to delete a line, delete it here, or paint over it in black here.  This is also where you will thin your detail lines if you need to create more line-weight.  The easiest way to do this is by using the magic wand with “contiguous” unchecked.  Then go to Select->Modify->Expand.  A little trial and error is needed here to find the right amount to reduce the line-weight without erasing them.  Once you have the right amount of expansion, make sure black is your background color, and hit delete to reduce the line-weight.  If you’re my method of a main line layer and a detail line layer, each will be set up this way, in one folder on the top of the layer stack.

Next time I’ll go over turf, and give the technique I use to erase the tiled look patterns normally create.

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