From 61d34c6a500d487c8952d4ad7751e1deb80f5bfc Mon Sep 17 00:00:00 2001
From: Lars Ingebrigtsen <larsi@gnus.org>
Date: Mon, 21 Mar 2022 17:51:21 +0100
Subject: [PATCH] Allow specifying the intermediate format

* lisp/image/image-converter.el (image-convert-to-format): New
user format (bug#54494).
(image-convert, image-converter--convert-magick)
(image-converter--convert): Use it.
---
 lisp/image.el                 |  3 ++-
 lisp/image/image-converter.el | 35 +++++++++++++++++++++++++++--------
 2 files changed, 29 insertions(+), 9 deletions(-)

diff --git a/lisp/image.el b/lisp/image.el
index fd0b5b67835..bad8ba7cd71 100644
--- a/lisp/image.el
+++ b/lisp/image.el
@@ -461,6 +461,7 @@ must be available."
     (and auto
 	 (or (eq auto t) (image-type-available-p type)))))
 
+(defvar image-convert-to-format)
 
 ;;;###autoload
 (defun create-image (file-or-data &optional type data-p &rest props)
@@ -498,7 +499,7 @@ Image file names that are not absolute are searched for in the
     (when (eq type 'image-convert)
       (require 'image-converter)
       (setq file-or-data (image-convert file-or-data data-format)
-            type 'png
+            type (intern image-convert-to-format)
             data-p t)))
   (when (image-type-available-p type)
     (let ((image
diff --git a/lisp/image/image-converter.el b/lisp/image/image-converter.el
index 460ff16adb0..b8c9a620024 100644
--- a/lisp/image/image-converter.el
+++ b/lisp/image/image-converter.el
@@ -46,6 +46,16 @@ formats that are to be supported: Only the suffixes that map to
   :type 'symbol
   :version "27.1")
 
+(defcustom image-convert-to-format "png"
+  "The image format to convert to.
+This should be a string like \"png\" or \"ppm\" or some
+other (preferrably lossless) format that Emacs understands
+natively.  The converter chosen has to support the format, and if
+not, conversion will fail."
+  :group 'image
+  :version "29.1"
+  :type 'string)
+
 (defvar image-converter-regexp nil
   "A regexp that matches the file name suffixes that can be converted.")
 
@@ -85,7 +95,10 @@ is a string, it should be a MIME format string like
        'image-convert))
 
 (defun image-convert (image &optional image-format)
-  "Convert IMAGE file to the PNG format.
+  "Convert IMAGE file to an image format Emacs understands.
+This will usually be \"png\", but this is controlled by the
+`image-convert-to-format' user option.
+
 IMAGE can either be a file name or image data.
 
 To pass in image data, IMAGE should a string containing the image
@@ -96,8 +109,8 @@ like \"image/webp\".  For instance:
 
 IMAGE can also be an image object as returned by `create-image'.
 
-This function converts the image to PNG, and the converted image
-data is returned as a string."
+This function converts the image the preferred format, and the
+converted image data is returned as a string."
   ;; Find an installed image converter.
   (unless image-converter
     (image-converter--find-converter))
@@ -120,7 +133,9 @@ data is returned as a string."
     (if (listp image)
         ;; Return an image object that's the same as we were passed,
         ;; but ignore the :type value.
-        (apply #'create-image (buffer-string) 'png t
+        (apply #'create-image (buffer-string)
+               (intern image-convert-to-format)
+               t
                (cl-loop for (key val) on (cdr image) by #'cddr
                         unless (eq key :type)
                         append (list key val)))
@@ -239,12 +254,15 @@ Only suffixes that map to `image-mode' are returned."
                                  (list (format "%s:-"
                                                (image-converter--mime-type
                                                 image-format))
-                                       "png:-"))))
+                                       (concat image-convert-to-format
+                                               ":-")))))
                      ;; SOURCE is a file name.
                      (apply #'call-process (car command)
                             nil t nil
                             (append (cdr command)
-                                    (list (expand-file-name source) "png:-")))))
+                                    (list (expand-file-name source)
+                                          (concat image-convert-to-format
+                                                  ":-"))))))
       ;; If the command failed, hopefully the buffer contains the
       ;; error message.
       (buffer-string))))
@@ -262,14 +280,15 @@ Only suffixes that map to `image-mode' are returned."
                                 (append
                                  (cdr command)
                                  (list "-i" "-"
-                                       "-c:v" "png"
+                                       "-c:v" image-convert-to-format
                                        "-f" "image2pipe" "-"))))
                      (apply #'call-process
                             (car command)
                             nil '(t nil) nil
                             (append (cdr command)
                                     (list "-i" (expand-file-name source)
-                                          "-c:v" "png" "-f" "image2pipe"
+                                          "-c:v" image-convert-to-format
+                                          "-f" "image2pipe"
                                           "-")))))
       "ffmpeg error when converting")))
 
-- 
2.39.2