Howdy, folks. I'm using ImageMagick via rmagick to chop up large images
into tiles suitable for viewing using the zoomify flash viewer. It's all
working fine, except for the fact I'm producing images whose files are
5-6 times as large as those produced by the windows program.
The relevant snippets of code are:
image = Magick::Image.read(filename).first
levels = (Math.log([image.rows, image.columns].max.to_f / TILESIZE) /
Math.log(2)).ceil
...
(0..levels).each do |level|
n = levels - level
# Obtain the image to tile for this level. The 0th level should
consist
# of one tile, while the highest level should be the original image.
level_image = image.resize(image.columns >> n, image.rows >> n)
tiles(tmpdir, level, level_image) do |filename|
...
end
# Rmagick needs a bit of help freeing image memory.
level_image = nil
GC.start
end
# Splits the given image up into images of TILESIZE, writes them to
the
# given directory, and yields their names
def self.tiles(dir, level, image)
slice(image.rows).each_with_index do |y_slice, j|
slice(image.columns).each_with_index do |x_slice, i|
# The images are named "level-column-row.jpg"
filename = "#{level}-#{i}-#{j}.jpg"
tile_image = image.crop(x_slice[0], y_slice[0], x_slice[1],
y_slice[1])
tile_image.write("#{dir}/#{filename}") do
# FIXME - the images end up being 4-5x larger than those
produced
# by Zoomifier EZ and friends... no idea why just yet, except
to note
# that the density of these tiles ends up being 400x400, while
# everybody else produces tiles at 72x72. Can't see why that
would
# matter though...
self.quality = 90
self.colorspace = Magick::RGBColorspace
self.compression = Magick::JPEGCompression
self.density = '72x72'
end
# Rmagick needs a bit of help freeing image memory.
tile_image = nil
GC.start
yield filename
end
end
end
I'll note that the tile images produced by the windows program claim a
density of 72x72, while my images claim a density of 400x400.
Can anyone suggest what I may be doing incorrectly, or ways I might go
about diagnosing the problem? Many thanks.
- donald
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