I want to scale the sprite 8x with padding between pixels - imagemagick

Question

There is a small sprite:
# mario sprite in base64 writing to file:
magick 'inline:data:image/png;base64,
iVBORw0KGgoAAAANSUhEUgAAABQAAAAUCAYAAACNiR0NAAAACXBIWXMAAA7EAAAO
xAGVKw4bAAAA00lEQVQ4ja1UwRGDMAyTe7zLJmWUzMoodBO6gHmkhsRWcukVvYID
kiKbiKoqbsTjTjIAmLq7IvXzwGHahJ5sUKBJKKhf3rcVAPB8pZ5BTihyEcxLomuD
Fxhqyryk06WtDZ93LSB+bMqYvBtPBsQYA2FP3YPl2XUIAIpcsCZ5eRM18slvALyL
CoFAu5EApCn7tsbx+hY0U55llmkYG7NefuhzKAVFUv1Mm8L+EgKWa5zDQbIWqiNn
riuvID8g1r4c2Hi6Ghvg6sg/mqEIDv+9v2+/sQ8vtmAvY/Wf0QAAAABJRU5ErkJg
gg==' mario.png
I want to scale it 8x:
convert -scale 800% -quality 100 mario.png mario-big.png
But scale with padding between pixels. To have an indent of 1 pixel between four adjacent eight times larger pixels. Or overlay a grid over the enlarged image.
How can I do this, please tell me?
Example:

Answer 1

As an alternative approach, how about using -fx to make a grid? For example:
convert -size 64x64 canvas: -fx "i % 9 == 0 | j % 9 == 0" x.png
Will set a pixel white when either the column (that's i) or row number (that's j) is on a multiple of 9. I see:
Now using Mark's suggestion, just expand your sprite by 9 with nearest neighbor, then use a ternary operator to pick either the image (image pixels are u) or white (1.0):
convert mario.png \
-scale 900% \
-fx "(i % 9 == 0 | j % 9 == 0) ? 1.0 : u" \
result.png
With this test image:
I see:
It'll work for any size image, though it'll be pretty slow if the image is large.

Answer 2

Updated Answer
I'm not sure how to change the 2px spacing to 1px in my original answer. Here's another method which we can probably speed up and improve if it gets the results you want. I'm using my image below as it's a an easier size to see, but you can adjust the numbers to match your own image. I am also using the "wrong" colours so you can see where each one ends up, but again, you can change my mad colours to white:
Chop into rows, each row being 50px tall
Iterate over rows, chopping each into 50px wide chunks and recombining with 1px yellow spacing
Smush the new rows together vertically with 1px cyan spacing
The code looks like this:
#!/bin/bash
# Chop into rows, each row being 50px tall
magick artistic-swirl.jpg -crop x50 row-%02d.png
# Iterate over rows, chopping each into 50px wide chunks and recombining with 1px spacing
for f in row-*png ; do
echo $f
magick "$f" -crop 50x -background yellow +smush 1 "$f"
done
# Smush the new rows together vertically with 1px spacing
magick row-*png -background cyan -smush 1 result.png
Note that +smush N joins images side-by-side with N px spacing in the background colour, but that -smush N joins images above-and-below with N px spacing.
Here's what I get applying that to your image:
#!/bin/bash
# Chop into rows, each row being 50px tall
magick mario.png -scale 800% -crop x8 row-%02d.png
# Iterate over rows, chopping each into 50px wide chunks and recombining with 1px spacing
for f in row-*png ; do
echo $f
magick "$f" -crop 8x -background yellow +smush 1 "$f"
done
# Smush the new rows together vertically with 1px spacing
magick row-*png -background cyan -smush 1 -bordercolor blue -border 1 result.png
Original Answer
Not at a computer to test, but if you scale your image up to the correct size as you are currently doing, you should then be able to crop the image into tens/hundreds of individual 8x8 images and pipe them to a montage command to lay them out on a white background with a 1px spacing between all the individual 8x8 blocks.
Something like:
magick 'inline:data:...' -scale 800% -crop 8x8 miff:- | magick montage -background white -geometry +1+1 -tile Nx miff:- result.png
where N is the number of 8x8 blocks you want in each row.
Note that miff:- is an ImageMagick internal lossless transmission format.
Back at a computer, I'll do something similar with this image:
magick artistic-swirl.jpg -scale 500x500 -crop 50x50 miff:- | magick montage -background yellow -geometry +5+5 -tile 10x miff:- result.png