How to set image size in result of src block in Org mode

Question

I've got a src block that has an image file as a result and I want that image file to be exported as a certain size.

I know I could apply the property #+ATTR_HTML: :width 100px, but I can't figure out a way to do that automatically when the result is produced.

The specific src block I'm using probably isn't necessary for an answer, but here it is anyway.

#+BEGIN_SRC python :noweb no-export :results file :exports both
<<extract-cells-from-table>>
image = cv2.imread("resources/examples/example-table.png", cv2.IMREAD_GRAYSCALE)
cell_images_rows = extract_cell_images_from_table(image)
cv2.imwrite("resources/examples/example-table-cell-1-1.png", cell_images_rows[1][1])
"resources/examples/example-table-cell-1-1.png"
#+END_SRC

#+RESULTS:
[[file:resources/examples/example-table-cell-1-1.png]]

Answer 1

I've figured out something that works but isn't perfect.

#+NAME: html-image-size
#+BEGIN_SRC emacs-lisp :var text="" :var width="100%" :var height="100%" :results raw
(concat "#+ATTR_HTML: :width " width " :height " height "\n[[file:" text "]]")
#+END_SRC

Then I can set the :results of a src block to raw and add that emacs-lisp src block as a :post header arg.

#+BEGIN_SRC python :noweb-ref test-detect-table :noweb yes :results raw :post html-image-size(text=*this*, width="300px")
import cv2

<<detect-table>>

image_filename = "resources/examples/example-page.png"
image = cv2.imread(image_filename, cv2.IMREAD_GRAYSCALE)
image = find_tables(image)[0]
cv2.imwrite("resources/examples/example-table.png", image)
"resources/examples/example-table.png"
#+END_SRC

That is almost perfect. The only thing I've noticed that I lose is org-babel-remove-result no longer works. It just removes the #+RESULTS: line while the file link remains.

Anyone know of a solution to that?

Edit: Found a solution.

There's no configurable option. There is a defconst regex that org-babel uses to find the start/end of result blocks. But I wrote a function to remove the #+ATTR.* lines that were causing the built-in regex to fail.

(defun remove-attributes-from-src-block-result (&rest args)
  (let ((location (org-babel-where-is-src-block-result))
        (attr-regexp "[     ]*#\\+ATTR.*$"))
    (when location
      (save-excursion
        (goto-char location)
        (when (looking-at (concat org-babel-result-regexp ".*$"))
          (next-line)
          (while (looking-at attr-regexp)
            (kill-whole-line)))))))

(advice-add 'org-babel-remove-result :before #'remove-attributes-from-src-block-result)
(advice-add 'org-babel-execute-src-block :before #'remove-attributes-from-src-block-result)

Answer 2

:wrap "org \n#+ATTR_HTML: :width 200"

seems to work:

#+begin_src mermaid :background-color transparent :wrap "org \n#+ATTR_HTML: :width 200" :file test..nogit..png
sequenceDiagram
 A-->B: Works!
#+end_src

#+RESULTS:
#+begin_org 
#+ATTR_HTML: :width 200
[[file:test..nogit..png]]
#+end_org