Scaling Down an Image for Processing

[r.e.]

This came up in a current thread on an unrelated issue, in which Matus Kalinsky commented:

I have recently (finally) adopted the strategy where you scale down the original image (as a copy - you keep the original master file of course), do all your adjustment (levels, curves, adjustment levels, masks, etc ...) and once you are happy with that you scale it up again and paste the original image in as a new layer - so only the very last steps (final cropping, sharpening, etc) will take long. It really helps when your original image is 2000 dpi scan from 4x5 (cca 70 Mpix image - 400MB in 48bit color mode)

I haven't come across this idea before. Could someone elaborate a little on how this is done? Are there downsides/things to look out for?

Thanks.

[Mike1234]

It's nothing new but keep in mind this doesn't apply to noise filtering, sharpening, etc. Otherwise it's okay but it's a moot point if you have a really decent machine.

[poco]

http://www.youtube.com/watch?v=GqWrh7OG5yQ

http://www.youtube.com/watch?v=-UNXJdTQKuw

[onnect17]

I think I'm mising something here. If you scale down you will loose information, right?

[Mike1234]

Scaling down/up has no affect on adjustment layers and usually little affect on mask accuracy... maybe some tweaking after resizing upward. The idea suggested is to do all your masking/adjusting on a smaller image (because it takes fewer computing cycles) then resize it back to original and paste the original image onto the backdround. Again though if you have a speedy computer then, IMHO, the image would have to be quite large and/or with many layers to make it worth while. Ehh... maybe I just work too slowly.

[SteveKarr]

SWEET ! I have this problem all the time ... Not NO More!!

Thanks for sharing ....

I have a MacBookPro 2.5gig with 4 gig ram, but it chokes in 300meg scans in 16bit

[Mike1234]

You need more RAM. Upgrading to 8 gigs will avoid HD caching with images totaling 700MB or a bit bigger if you're not multitasking with other memory hogs. I know this is stating the obvious but you'll need a 64 bit OS and the other HW to support it.

[Daniel Moore]

Rich Seiling at West Coast Imaging calls this a guide file workflow. Among the many excellent tips and tutorials you can find there.
http://www.westcoastimaging.com/wci/...guidefile.html

[Sylvester Graham]

You could record an action script on the smaller image and then use it on the larger...