Carrierwave PNG to JPG converter. How to avoid black background?

Question

In paperclip, for example, it is possible to add this to set white background when .png is converted to .jpg:

:convert_options => { :all => '-background white -flatten +matte'}

Once carrierwave uses rmagick too, how to do that?

Obs.: My files are being stored in S3.

My code:

version :square do
    process :resize_to_fill => [200, 200]
    process :convert => 'jpg'
end

Answer 1

Here's saner version that only does the conversion and background filling

def convert_and_fill(format, fill_color)
  manipulate!(format: format) do |img|
    new_img = ::Magick::Image.new(img.columns, img.rows)
    new_img = new_img.color_floodfill(1, 1, ::Magick::Pixel.from_color(fill_color))
    new_img.composite!(img, ::Magick::CenterGravity, ::Magick::OverCompositeOp)
    new_img = yield(new_img) if block_given?
    new_img
  end
end

Example usage:

process convert_and_fill: [:jpg, "#FFFFFF"]

Answer 2

Using MiniMagick, I can just do this:

process :resize_and_pad => [140, 80, "#FFFFFF", "Center"]