Trouble making an efficient BAT file to overlay images

[Taruby]

I'm trying to create a BAT file to overlay a specific series of transparent .png files over a specific series of background .png files.

This is what the BAT file will look like with my current knowledge:

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convert Original\image_001.png Overlay\image_001.png -gravity center -composite Result\image_001.png
convert Original\image_002.png Overlay\image_002.png -gravity center -composite Result\image_002.png
..
convert Original\image_999.png Overlay\image_999.png -gravity center -composite Result\image_999.png

I don't want to write 999 individual lines, but I don't know enough about coding to figure out what terms I need to google to figure out how to make it so I can perform the above using fewer lines of code.

EDIT: Thank you snibgo for the correction regarding the right order of the operators.

[snibgo]

You have "-composite" in the wrong place. It should be the last thing before the output name, thus:

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convert Original\image_001.png Overlay\image_001.png -gravity center -composite Result\image_001.png

[Taruby]

Thank you very much for the correction regarding the correct order of the operators, snibgo! Despite being in the incorrect position, the BAT still worked when I tested it earlier, so I didn't notice I made a mistake.

This is my current progress to making an efficient BAT file:

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for /L %%n in (1,1,999) do convert Original\image_%%n.png Overlay\image_%%n.png -gravity center -composite Result\image_%%n.png

I need to figure out how to get it to read file names with padded zeros, i.e. "001, 002.. 999". For some reason, it wants to read them numbered as "1, 2.. 999". I'm having a difficult time wrapping my head around this.

[snibgo]

I don't know of any way to force "for" variables to have leading zeros. You can do it manually, in three steps.

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for /L %%n in (1,1,9) do convert Original\image_%%n.png Overlay\image_%%00n.png -gravity center -composite Result\image_%%00n.png

for /L %%n in (10,1,99) do convert Original\image_%%n.png Overlay\image_%%0n.png -gravity center -composite Result\image_%%0n.png

for /L %%n in (100,1,999) do convert Original\image_%%n.png Overlay\image_%%n.png -gravity center -composite Result\image_%%n.png

Or you could do it with a single "for" loop, creating a variable within the loop, setting it to %%n with the appropriate number of leading zeros.

[Taruby]

The three step method works satisfactorily for what I'm trying to accomplish. Thank you very much for your help, snibgo! It's appreciated. =)

[snibgo]

Here is a more elegant method of adding leading zeros.

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for /L %%n in (1,1,999) do (
set NUM=000%%n
set NUM=!NUM:~-3!
echo !NUM!
convert Original\image_!NUM!.png Overlay\image_!NUM!.png -gravity center -composite Result\image_!NUM!.png
)

This ensures we have 3 digits. To ensure we have (x, where x is an integer > 1) digits, put at least (x-1) zeros in the first "set NUM", and change "3" to "x" in the second "set NUM".