我正在尝试通过RMagick将图像转换为25％的不透明度。以下内容可从命令行运行，但我不知道如何在Ruby中执行。
convert input.png -alpha on -channel A -evaluate set 25% +channel output.png
我曾尝试将Magick::AlphaChannelType::ActivateAlphaChannel弄乱，但不知道如何将命令链接在一起。任何帮助将不胜感激！
请尝试使用此功能解决您的问题
def watermark(opacity = 0.25, size = 'input')
manipulate! do |img|
logo = Magick::Image.read("#{Rails.root}/app/assets/images/{size}.png").first
logo.alpha(Magick::ActivateAlphaChannel)
white_canvas = Magick::Image.new(logo.columns, logo.rows) { self.background_color = "none" }
white_canvas.alpha(Magick::ActivateAlphaChannel)
white_canvas.opacity = Magick::QuantumRange - (Magick::QuantumRange * opacity)
# Important: DstIn composite operation (white canvas + watermark)
logo_opacity = logo.composite(white_canvas, Magick::NorthWestGravity, 0, 0, Magick::DstInCompositeOp)
logo_opacity.alpha(Magick::ActivateAlphaChannel)
# Important: Over composite operation (original image + white canvas watermarked)
img = img.composite(logo_opacity, Magick::NorthWestGravity, 0, 0, Magick::OverCompositeOp)
end
end