Default Inline Image Background in Org Mode

Question

When an image has a transparent background, Emacs of course respects that.

Unfortunately, this can lead to issues with display:

Is there a way to display a specific color (e.g. white) behind the image? There appears to be some support for it in ImageMagick images.

The specific stuff I'm working with right now can have the background color set, however I have to add an extra few lines to every single figure in order to do that, which is less than ideal. I would like to get it to where inline images displayed in org-mode have the background color set by default.

(Note: this isn't org-babel specific, it just happens to be how I'm getting these images right now)

Answer 1

After much digging, there does not appear to be a built-in option to adjust this in Org or in general. The image system does not have any way to customize the default background, and org doesn't have a way to set the :background property. However, it does look like most images support the :background display property.

I added this functionality to Org by modifying (read: copy and paste into .emacs.d with a 1-line change) org-display-inline-images.

I won't reproduce the function here, because it is rather lengthy. Line 51 of the function reads:

(setq img (save-match-data (create-image file type nil :width width)))

I defined a new customizable variable org-inline-image-background, which can hold either nil (transparent background) or a color:

(defcustom org-inline-image-background nil
  "The color used as the default background for inline images.
  When nil, use the default face background."
  :group 'org
  :type '(choice color (const nil)))

Then, I added it to line 51:

(setq img (save-match-data (create-image file type nil :width width 
                                                       :background org-inline-image-background)))

This works beautifully and it can be customized using the color picker, so it satisfies all my requirements.

Answer 2

I got a better solution with advice.

(defcustom org-inline-image-background nil
  "The color used as the default background for inline images.
When nil, use the default face background."
  :group 'org
  :type '(choice color (const nil)))

(defun create-image-with-background-color (args)
  "Specify background color of Org-mode inline image through modify `ARGS'."
  (let* ((file (car args))
         (type (cadr args))
         (data-p (caddr args))
         (props (cdddr args)))
    ;; Get this return result style from `create-image'.
    (append (list file type data-p)
            (list :background (or org-inline-image-background (face-background 'default)))
            props)))

(advice-add 'create-image :filter-args
            #'create-image-with-background-color)