Implement image-size for Emacs without image support

[jaeyeom]

Can `image-size' function be implemented for Emacs without the image support? The code should check if image-size is bounded, otherwise it should use "magick" tool to implement it. The help message of image-size function in other system with the image support looks like the following:

image-size is a primitive-function in ‘C source code’.

(image-size SPEC &optional PIXELS FRAME)

Return the size of image SPEC as pair (WIDTH . HEIGHT).
PIXELS non-nil means return the size in pixels, otherwise return the
size in canonical character units.

FRAME is the frame on which the image will be displayed. FRAME nil
or omitted means use the selected frame.

Calling this function will result in the image being stored in the
image cache. If this is not desirable, call ‘image-flush’ after
calling this function.

Probably introduced at or before Emacs version 21.1.

[back]

[jaeyeom]

Resolution: image-size fallback implementation

I've successfully implemented a fallback solution for the image-size function that works in Emacs without image support (like text terminals and batch mode).

Implementation

Created image-size-fallback.el which provides:

1. Automatic fallback detection: Detects when the built-in image-size function is not available or not working
2. External tool support: Uses magick or convert commands to determine image dimensions
3. Compatible API: Maintains the same function signature as the built-in image-size function
4. Multiple image spec formats: Supports file paths, create-image specs, and plist specs
5. Error handling: Proper error messages when images can't be processed

Usage

;; Load and install the fallback
(load "image-size-fallback.el")
(image-size-fallback-install)

;; Now image-size works even in batch mode or text terminals
(image-size "image.png")         ;; Returns (width . height)
(image-size (create-image "image.png"))  ;; Also works

Testing

Tested successfully with:

• Emacs batch mode (emacs -Q --batch)
• Different image formats (PNG, JPEG)
• Various image specification formats
• Error handling for missing files
• Both magick and convert commands

The implementation automatically detects when the fallback is needed and only installs itself when the built-in image-size function is not working in the current environment.

Files Created

• image-size-fallback.el: Main implementation
• demo-image-size.el: Demonstration script

Perfect for environments like Termux where Emacs runs in text mode without native image support!