this is  : vermilion sands | photodesk feedback  : photodesk@iconbar.com hosted by  : the iconbar now  : updated  : sun 05 may 2002 5:29pm bst go  : home | tutorials | spotlights with masks

Spotlights with Masks

One way of emphasing part of an image is to simulate lighting. Here are two simple methods of shining a 'spotlight' on part of a picture. The first uses a mask, and the second (and better) uses layers.

Two David Hardy paperweights [March 2002; Fuji FinePix 2300 digicam]

• Load your image into Photodesk. Use this one if you like -- it shows two paperweights produced by famous astronomical artist David Hardy, the one on the left commemorating the Zambian total solar eclipse of 2001, at which we were also present. It was a wedding present from our friend Julie.
• Click on the Montage (scissors) icon, then the Copy icon (two rectangular outlines).
• In the Copy window, select Feather and change to about 50 pixels.
• Now click on the Solid ellipse tool, and draw an ellipse around the two paperweights:

  

  Selecting an ellipse

• Photodesk's ellipse tools are mislabelled slightly: they show a slanted ellipse, but the tools are only capable of drawing ellipses with horizontal or vertical axes. So while we're about it here's how to draw a rotated ellipse (and rotated squares, for that matter).
• Click on the Cross, then on the Rubber stamp. You'll find that whatever was last drawn (in this case an ellipse) has been set up as a stamp. Stamps have handles, as in Draw, and can be rotated by grabbing the top 'ear' and scaled with the bottom one. Grab the top ear and turn it slightly:

  

  Rotating the ellipse

• When you're satisfied, click on Apply to confirm the selection.
• Now go to the Copy window, and open the pull-down menu. Click on Save to>#4 Alpha, and your image should take on a pink tinge as the mask channel is changed.
• Click on the Palette to return to painting mode.
• We want to protect the area bounded by the ellipse, so we need to invert the mask. Either open the main image menu and select Mask>Invert or type Ctrl-Shift-I.
• The mask display gets in the way, so either select Mask>Hide from the main image menu, type Ctrl-Shift-H, or open the Channels window and click on the Eye of channel #4.
• Click on the Image processing toolbar icon (the bar graph), ensure Linear equalisation is selected, and click on Details.
• Drag the bottom of the right-hand dotted line leftwards, about halfway across:

  

  Dimming the image

• The idea here is to dim all of the image apart from the bits we want to look 'lit'. If you want, Preview the effect (though note that the preview ignores the mask) and move the dotted line to suit.
• Apply with the Magic wand set to Whole image; if you've previewed it you'll need to click twice. You should get something like this:

  

  Spotlit paperweights

Notes

• This technique is very general. All you need to do is draw the areas you want illuminated into the mask channel, with fading (use the Gradient effect as well as feathering, as here) and smoothing available to give more or less realistic effects.
• You can move the 'spotlight' around by holding down Ctrl-Shift and dragging with Select.
• Note that this isn't an accurate illumination model. For example, adding highlights to the glass in the image here would increase the realism, as would a few shadows. The shadows can be done with careful use of the mask, and highlights can be added with judicious use of the glint airbrush described earlier.