Watermark images with ImageMagick 'convert' using 'composite', 'watermark' and 'dissolve' in Ruby

watermark_with_image.rb

# Watermarking image with another image using Imagemagick 'composite', 'watermark' and 'dissolve'.
require "RMagick"

# Read the image in the memory with RMagick
img = Magick::Image.read("/home/aditya/Pictures/old_england_pic.jpg").first

# the original image was in jpg format
# need to make the white background color transparent
# also changed the format to png since JPG does not support transparency.
# run the command below to create an image with transparent background using ImageMagick
# convert cc.png -transparent white -fuzz 2% watermark.png

mark = Magick::Image.read("/home/aditya/Pictures/watermark.png").first

# set the canvas to transparent
# if we do not specify 'background_color' on 'mark' then on rotation the background color will be black.
# we want it to be transparent.
mark.background_color = "Transparent"

# resize the watermark to 60% of the image we want to watermark

watermark = mark.resize_to_fit(img.rows * 0.6, img.columns * 0.6)

# rotate this mark by 45 degrees anticlockwise (optional)
watermark.rotate!(-45)

# using composite
# place the watermark in the center of the image
# default 'compose over' overlays the watermark on the background image
# SoftLightCompositeOp darkens or lightens the colors, dependent on the source color value.
# If the source color is lighter than 0.5, the destination is lightened.
# If the source color is darker than 0.5, the destination is darkened, as if it were burned in.
# The degree of darkening or lightening is proportional to the difference between the source color and 0.5.
# If it is equal to 0.5, the destination is unchanged.
# Painting with pure black or white produces a distinctly darker or lighter area, but does not result in pure black or white.
img1 = img.composite(watermark, Magick::CenterGravity, Magick::SoftLightCompositeOp)
# save the watermarked image
img1.write("/home/aditya/Pictures/wm_old_england_pic_image_composite.jpg")

# using watermark
# place the watermark in the center of the image with gravity
# watermark the image with 20% brightness and 30% saturation
img2 = img.watermark(watermark, 0.2, 0.3, Magick::CenterGravity)
# save the watermarked image
img2.write("/home/aditya/Pictures/wm_old_england_pic_image_watermark.jpg")

# using dissolve
# add watermark with 40% opacity for watermark, 100% opacity for image and position is center
img3 = img.dissolve(watermark, 0.4, 1, Magick::CenterGravity)
# save the watermarked image
img3.write("/home/aditya/Pictures/wm_old_england_pic_image_dissolve.jpg")

watermark_with_text.rb

# Watermarking image with text using ImageMagick 'composite', 'watermark' and 'dissolve'
require "RMagick"

# Read the image in the memory with RMagick
img = Magick::Image.read("/home/aditya/Pictures/old_england_pic.jpg").first

# Create a new image in memory with transparent canvas
# size of this 'mark' image is same as original image which we want to watermark
mark = Magick::Image.new(img.rows, img.columns) {self.background_color = "none"}
draw = Magick::Draw.new

# draw is used to add elements to an image like text
draw.annotate(mark, 0, 0, 0, 0, "creative commons") do
  # place the text in the centre of the canvas
  draw.gravity = Magick::CenterGravity
  # set text height in points where 1 point is 1/72 inches
  draw.pointsize = 100
  draw.font_family = "Times" # set font
  draw.fill = "black" # set text color
  draw.stroke = "none" # remove stroke
end

# rotate this mark by 45 degrees anticlockwise (optional)
# if we do not specify 'background_color' on 'mark' then on rotation the background color will be black.
# we want it to be transparent.
mark = mark.rotate(-45)

# using composite
# place the watermark in the center of the image
# default 'compose over' overlays the watermark on the background image
# SoftLightCompositeOp darkens or lightens the colors, dependent on the source color value.
# If the source color is lighter than 0.5, the destination is lightened.
# If the source color is darker than 0.5, the destination is darkened, as if it were burned in.
# The degree of darkening or lightening is proportional to the difference between the source color and 0.5.
# If it is equal to 0.5, the destination is unchanged.
# Painting with pure black or white produces a distinctly darker or lighter area, but does not result in pure black or white.
img1 = img.composite(mark, Magick::CenterGravity, Magick::SoftLightCompositeOp)

# save the watermarked image
img1.write("/home/aditya/Pictures/wm_old_england_pic_text_composite.jpg")

# using watermark
# place the watermark in the center of the image with gravity
# watermark the image with 20% brightness and 50% saturation
img2 = img.watermark(mark, 0.2, 0.5, Magick::CenterGravity)
# save the watermarked image
img2.write("/home/aditya/Pictures/wm_old_england_pic_text_watermark.jpg")

# using dissolve
# add watermark with 25% opacity for watermark, 50% opacity for image and position is center
img3 = img.dissolve(mark, 0.25, 0.5, Magick::CenterGravity)
# save the watermarked image
img3.write("/home/aditya/Pictures/wm_old_england_pic_text_dissolve.jpg")