|This section describes my favorite manual techniques in Photoshop for enhancing digitally-generated shaded relief. To a large extent, the look of any given shaded relief is governed by the immutable topographic characteristics of the area it represents. Like it or not, geographic reality often dictates graphic reality. All other factors being equal, I prefer shaded relief that contains a mix of flatlands, foothills, and mountains in roughly equal proportionscreating, in a sense, a topographical "golden mean." The least satisfying shaded relief to depict, for me, is repetitive, undulating topography. Most shaded relief depicts landscapes somewhere between these two extremes. The before and after examples below show how typical problem shaded relief can be enhanced manually to appear more legible and graphically pleasing.
1) Santa Cruz Island, California
|Problem: Primary slopes and drainage basins often lack definition on digital shaded reliefs of eroded or complex landscapes. Relief derived from small-scale GTOPO30 showing northern mountain areas, such as the Rocky Mountains of western Canada, are especially susceptible. The dense detail obscures macro topographyit is impossible to see the forest for the trees.
Solution: The airbrush tool was used to spray a mist of darker tones over the shadowed slopes to tie together the many small ridges and gullies as a single macro topographic formation. My goal was to better define the northern and southern mountain ranges separated by an east-west oriented central valley. Additional dark tone was sprayed in the uppermost reaches of the shadowed slopes to enhance the aerial perspective effect. Value was removed from the highest illuminated slopes, further enhancing aerial perspective, by lightly applying the dodge tool repeatedly in a downslope direction. Finally, to better define the northwest peninsula's mountainous spine, the illumination source was locally rotated from northwest to north (shown by the arrows).
|2) Santa Cruz Island (drainage detail), California
|Problem: Vector drainage lines and raster shaded relief are misregistered to one another, regardless of slight global adjustments to their scale or position.
Solution: Two approaches may be used to correct this problem: edit the drainage to fit the relief, or edit the relief to fit the drainage. Of these, the first approach is most common, simply because most cartographers are more comfortable editing vectors than raster images. However, this may not be the optimal solution. On many maps vector information is more accurate and of higher importance to the audience than shaded relief, which is printed lightly merely hinting at the topographical context (sad, but true). Editing vector drainage to fit the relief often sets off a chain reaction of additional unwanted adjustments, compromising map accuracy. For example, a road adjacent to an edited drainage may also need to be moved for reasons of limited space, which might in turn necessitate moving a political boundary. . . and so on.
Instead, I prefer adjusting shaded relief to fit drainage lines. Before editing can begin, vector drainages need to be rasterized and imported into the Photoshop relief file with pixel-perfect accuracy.
Importing vector drainage into Photoshop:
1) Place raster shaded relief (at the final size and dpi) in an Adobe Illustrator map file. Visually register the shaded relief as accurately as possible to the drainage lines. Do NOT rescale the relief in Illustrator. If changes are needed you should rescale the original relief file in Photoshop and place it again in Illustrator.
2) On a new layer in Illustrator draw a box at exactly the same dimensions as the placed shaded relief file. Register the box to the shaded relief. The box should be stroked (any color and line weight will do) and unfilled.
3) With the box selected, make crop marks (Object/Crop Marks/Make).
4) Delete (or turn off) the shaded relief layer and all other layers except the drainage (stroked as thin black lines). Save a copy of the file with a different name. Quit Illustrator.
5) Launch Photoshop. Open the Illustrator file you just saved at the same size, resolution, and color mode as the shaded relief. Copy and paste the rasterized drainage into the shaded relief file and set the new layer to multiply mode. The drainage now can be seen surprinting the relief just as it appeared in Illustrator.
Note: Photoshop 4.0 is better at rasterizing Illustrator files than versions 5.0, 5.5, and 6.0. These later versions apply a rounding error that slightly distorts the height or width of files, effectively making them useless for precise cartographic work. For example, take a 10 x 15" filled rectangle (no stroke) created in Illustrator and opened in Photoshop 6.0 at 200 dpi. This yields a rasterized image 2,000 x 3,002 pixels in size rather than the correct 2,000 x 3,000 size. I keep a copy of PS 4.0 on a Zip disk solely for rasterizing Illustrator files. Once vector files have been rasterized in Photoshop 4.0 correctly, they are safe to be opened in a newer "downgraded" version of Photoshop.
Now the fun begins. Use either the Airbrush tool or the Dodge and Burn tool(s) to add or subtract value from slopes, fitting the valley bottoms snugly to drainage lines. A soft brush applied with very light opacity works best to avoid making the valley bottoms appear too sharp. Extend small ridges and gullies downslope to the drainage lines, keeping their orientation consistent with the topography above, adding, perhaps, a touch of downstream flair to the bottommost slopes to enhance realism.
When relief touchups are completed discard the drainage layer and save the edited file. If the name of the Photoshop file is the same, Illustrator will automatically update the relief when launched.
|3) Hanalei Bay, Kauai, Hawaii
|Problem: Based on quality, not all DEMs are created equal. The USGS classifies the quality of its DEMs as Level 1 (low) or Level 2 (high), depending on how they are produced. Level 1 DEMs suffer from a variety of nasty problems that adversely affect graphic quality of derivative shaded relief in the form of artifacts (unwanted blemishes). Typical artifacts include gaps and uneven elevations between adjacent DEMs (a.k.a. edge matching); conspicuous spikes and holes on otherwise regular topographic surfaces, rice paddy-like terracing on gentle slopes (a.k.a. stair stepping), systematic banding (a.k.a. striping or raking); and, pebbly textures in lowlands (a.k.a. noise). Adding insult to injury, the lousiest Level 1 DEMs often seem to be found in the most important or topographically spectacular areas. Patterson's Principle: DEM quality is inversely related to a landscape's scenic beauty.
The DEM for Hanalei Bay shown above adheres to my principle. This exceptionally scenic area, where the movie South Pacific was filmed, contains severe horizontal systematic banding on mountain slopes (despite appearances, they have never been plowed) and a grainy noise fills flat lowland areas.
Solution: Removing DEM artifacts from shaded relief involves a tradeoff between showing detail and graphical cleanliness. In the case of Hanalei Bay, I used the median filter (Filter/Noise/Median) by an amount just large enough to remove the systematic banding, but not so large that it over generalized the relief. The median filter was applied to a duplicated relief layer under the original. By creating a layer mask on the original layer and painting on it with a soft semi-opaque brush, the generalized relief underneath was allowed to emerge through the original by varying amounts depending on the need to obscure artifacts at any given spot. Next, on a new layer, the airbrush tool with a semi-hard brush was used to add shadows and highlights to redefine topographic detail obliterated by the median filter. Finally, a light mist of the lowland gray value was sprayed over the bases of slopes to soften the abrupt transition to lowlands, enhancing the aerial perspective effect.
Tip 1: When removing terracing in lowlands, the procedure outlined above is better served with the softer blur filter (Filter/Blur/Gaussian Blur) than the median filter, which retains hard edges. Or, perhaps, a combination of the two filters can be applied.
Tip 2: Systematic banding can also be alleviated by directing the light source parallel to the bands, which in this case would be from the west. Of course, this means accepting a light source from a direction other than northwest.
Tip 3: Use the rubber stamp tool with a soft brush to carefully fill in holes, spikes, and gaps with nearby cloned tones of similar value.
|4) Simi and San Fernando Valleys, Los Angeles, California
|Problem: Dark lowlands are an effective device for making elevated landforms pop out in a three dimensional manner on a stand-alone shaded relief. However, when the shaded relief is later used on a map, the dark lowlands combine with surprinting cultural information that clusters in the lowlands (especially dense in the case of Los Angeles), to yield a graphically heavy, semi-legible product.
Solution: The lowland tones were diminished selectively without affecting the full range of tones found in the adjacent, mostly unpopulated San Gabriel Mountains. In the first step, selection boundaries were drawn around the lowland areas with the lasso selection tool. The irregular selection boundaries penetrate into the mountain valleys and were feathered to avoid an abrupt transition when lightening was applied using the Brightness/Contrast dialog (Image/Adjust/Brightness). Finally, after deselecting (Command-D) the lowland selections, I used the Dodge and Burn tool with a light soft brush to make subtle touchups. Although on a stand-alone relief the lightened lowlands are less effective for making topography appear to project upwards, this compromise is necessary to accommodate huge amounts of urban map information over-printing.
|Problem: The broad shield volcanos of Mauna Kea and Mauna Loa on the Big Island of Hawaii, just shy of 14,000 feet high and with bases on the sea floor 19,000 feet below the surface, are the most massive individual mountains on Earth. Low in amplitude and long in frequency, they are the topographic equivalents of a tsunamiwhich helps to explain their tremendous but largely invisible bulk. The relief shading challenge is to make the pancake-like profile of Mauna Loa appear volumetrically significant while preserving relatively minor surface details, such as volcanic cinder cones and Kilauea Crater. A similar problem is encountered on small-scale shaded relief of the coterminous U.S. The Great Plains gradually descend 5,000 feet between the Front Range of the Rocky Mountains and the Missouri River 500 miles to the east, forming a broad pedestal base for the continent, which the shadowing in digitally-generated relief inadequately depicts.
Solution: Using the Airbrush tool with a large soft brush, I applied dark and light tones in much the same manner as they appear on Santa Rosa Island (example 1), despite the different topography. After the gentle mid-elevation slopes were modeled to appear bulkier, I selectively sharpened (using the sharpen tool) the higher elevations to accentuate the volcanic details that were partially masked by the airbrushing. The illumination direction was locally rotated from northwest to west in Kohala and Hualalai to define their linear forms that trend northwest. However, the local illumination here could have been rotated toward the north with equal effectiveness, because no nearby landforms exist from which to guide the consistent application of highlights and shadows. Finally, to strengthen depth, I darkened coastal areas slightly on the illuminated side of the island, suggesting the classic dark to light (lowlands to highlands) hypsometric progression.
|6) Appalachian Mountains, Virginia
|Problem: Topographic detail is washed out by illumination striking linear slopes from a perpendicular direction. The extremely narrow ridges lack adequate breadth, graphically speaking, to convey a true impression about the relatively high local relief. A classic example of this problem can also be seen on small-scale shaded relief of the western U.S. As you travel eastward from the Willamette Valley of Oregon, the western slope of the Cascade Range rises gradually from near sea-level to an indistinct crest, punctuated here and there by volcanic summits, and then descends abruptly to the elevated High Desert not far below. Assuming standard northwest illumination, computer-generated shadowing on the narrow eastern slope of the Cascades lacks sufficient area and value to graphically portray the geographic significance of the range.
Solution: The challenge here is to find and show information where little exists. I relied on careful study and a pinch of imagination to identify which secondary topographic details (spur ridges and gullies) to emphasize. These details were strengthened by rotating the assumed light source from northwest to north, allowing subtle highlights and shadows to find purchase on the otherwise smooth slopes. I applied tones with the Airbrush tool and a medium-hard semi-opaque brush. Following the advice of the late John Sherman, who taught relief shading at the University of Washington, I airbrushed gully shading gradually diminishing in value upslope and extending nearly to the ridge tops, helping to tie the terrain together as a unit. To give the narrow ridges more body, I darkened the shadowed slopes slightly and feathered them downwards, increasing their basal width at the expense of the valleys. As always, I strengthened the aerial perspective effect by adding contrast and emhasizing serrations on the ridge crests, and by flattening contrast in lowland areas.
|7) The Abyss, Grand Canyon National Park
|Problem: Telling up from down on this digital relief is made difficult because of the unduly smooth plateau surface and the canyon bottom that is shown nearly as sharp as the rim. The unique world-famous topography of the Grand Canyon does not appear as distinctive as it could.
Solution: Instead of showing a Photoshop enhancement of the digital relief, I compare it to a manual relief (graphite and airbrush pigments on metal mount paper) drawn by Bill VonAllmen, my former NPS colleague now retired. Bill's relief contains roughly the same amount of topographic detail as the digital version, but is a more successful piece due to small graphical flourishes.
--The plateau surface is portrayed with a grainy flat texture. The fact that texture is visible on the plateau and not in the canyon subconsciously suggests that the plateau must be closer to map reader.
--Shadows and highlights on the rim receive stronger treatment than comparable slopes below. Also note that the very darkest shadows on the rim are used where the crests of spur ridges meet the rimthey just look right.
--Midtones model lower slopes at the head of The Abyss, emphasizing its amphitheater shape.
--The sinuous canyon bottom suggests dendritic drainage, which, of course, always lies in the lowest areas.
--Finally, emphasizing the steep horizontal ledges in mid slope helps to capture graphically the topographic essence of the Grand Canyon.