Add Shadow to Image


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Image file:
PNG or GIF images with bright colours and sharp edges usually yield the best results. JPEG images produce poor shadows since edges are not sharp and the background colour is indistinct. If you leave the file name blank, a sample image will be used; this permits experimenting with various settings without the need to upload your image file each time. In addition to PNG, GIF, and JPEG, you can also submit files in TIFF; X Windows Bitmap, Pixmap, and Window Dump formats; all variants of the PBMplus and Netpbm portable raster formats; and Silicon Graphics RGB format, assuming your browser is configured to understand them and you've given the file a name which identifies its contents to your browser. In case of difficulty, convert the file to PNG and try again.
Output image format:
JPEG images are usually smaller than PNGs but often contain unattractive artifacts of lossy compression, especially if the original image had sharp edges and and prominent colour contrasts. JPEG sometimes produces better results when translucent shadows or a small image scale is selected. GIF is provided for compatibility with legacy systems; files are smaller but limited in colour gamut.
Blur size:  0 = no blur, 25 = maximum blur
The larger the blur size, the more diffuse the shadow. A blur size of zero results in a sharp-edged shadow, as cast by the Sun.
Shadow offset: Horizontal: Vertical:
The offsets specify the number of pixels the shadow is shifted to the right and below the original image. If the image submitted does not contain sufficient space to the right and bottom to hold the shadow, it will be truncated. If unspecified, offsets default to half the blur size or two pixels, whichever is less.
Shadow colour:   Transmission:
By default, shadows are always black, as cast by opaque objects. If Translucent is selected, shadows take on the colour of the object which casts them. Depending on the image, this may create an attractive “stained glass” effect. Translucent shadows generally look best when the shadow is darkened compared to the casting object (as occurs due to absorption). The transmission field controls how much simulated light passes through the object. Transmission of 0.0, complete absorption, is equivalent to checking Black shadows, while 1.0, total transmission, yields shadows as bright as the casting object. Intermediate settings often produce the most attractive results.
Output image scale:
Shadow generation works best when the original image has sharp boundaries between the content and the background colour. After the shadow is added, the appearance of the image may be improved by resampling it into a smaller image, smoothing jagged edges by the averaging process. To create a smooth image with a good-looking shadow, prepare the original image at a larger scale than the image you want to publish, then select the corresponding image scale so the image with shadow is reduced in size to yield the desired image.


by John Walker
http://www.fourmilab.ch/