How can I interlace two images using ImageMagick?

Question

I have 2 images of the same size, called image1.png and image2.png. In ImageMagick, is there any way to merge the two images by taking the odd lines from image1.png and merge with the even line from image2.png ?

Answer 1

Sure, make alternate rows transparent:

# Make red test image
convert -size 300x200 xc:red red.png

# Make blue test image
convert -size 300x200 xc:blue blue.png

# Merge with alternate lines made transparent
convert red.png \( blue.png -alpha on -channel A -fx 'j%2' \) -composite result.png

Or, an alternative way of thinking about it is to load both images and then choose pixels from either the first (u) or the second (v) depending on the row:

convert red.png blue.png -fx 'j%2 ? u : v' result.png

On Windows, these two come out as:

REM Do Windows style commands
convert red.png ^( blue.png -alpha on -channel A -fx "j%2" ^) -composite result.png

and

REM Windows style
convert red.png blue.png -fx "j%2 ? u:v" result.png