single convert vs three convert - same result - same performance?

[agriz]

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convert image1.png [some process] image2.png
convert image3.png [some process] image4.png

convert image2.png -composite over image4.png

It uses three convert statement. If we write single convert for the above code, will both kind of codes require the same resource?

[snibgo]

Your second command is pointless, as image4.png will be overwritten (ignoring the possibility of multiple outputs).

[agriz]

Lets assume this.

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convert image1.png [some process] image2.png
convert image3.png [some process] image4.png

convert image2.png index4.png -composite over image5.png

[agriz]

Please tell how the performance varies for a output, which is written in multiple convert against single convert

[snibgo]

If you combine this into a single "convert image1.png image3.png {do_something} image5.png", you save:
- two invocations of the program
- one write to image2.png
- one write to image4.png
- one read of image2.png
- one read of image4.png

[agriz]

So single convert is always better?

[fmw42]

It is faster, saves write times, and should produce the exact same result provide you do not save intermediates in lossy compression such as jpg in your original commands.

[agriz]

Sir,

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convert -size 500x500 xc:none ( image.png -resize 100x100 ) -gravity center -compose Dst_Over -composite ( image2.png -resize 200x200 -gravity center -extend 200x200 ) -gravity center -compose Dst_Over -composite output.png

not working.

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convert -size 500x500 xc:none ( image.png -resize 100x100 ) -gravity center -compose Dst_Over -composite ( image2.png -resize 200x200 ) -gravity center -compose Dst_Over -composite output.png

working. Why the above one is not working?

[snibgo]

-extend 200x200

What is the error message? "-extend" is not a valid operation. Perhaps you intended "-extent".

[agriz]

it was -extent. I wrongly typed here.

There is no error message, The image (image2) just becomes white in the output.
If i swap and add -extent to image1 again image1 becomes white and image2 works. If i remove -extent it works good.
To use extent, do i need -gravity center?

-gravity center cause the trouble i guess.

[snibgo]

"-extent" is sensitive to the "-compose" setting. Do you really want Dst_Over for extent?

[fmw42]

Put -compose over before -extent.