Scanning Slides: Slow when scanning high resolution

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cullism

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When I first bought my CanoScan 8800F and set about scanning my old slides I was a bit enthusiastic and scanned at the default resolution. The resulting images, when printed, were poor quality. I have now started re-scanning all 124 slides at 4800dpi (or is it ppi?). The trouble is that when I enhance them or change their sizes Photoshop takes ages to complete the operation. Should I scan at 4800 or 2400 then resize the images to 600 before doing any enhancing? Is there some way to scan slides so that they print at an acceptable resolution but do not involve hours of waiting? I also want to burn the scanned images to a DVD.
 
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When images are scanned at low resolution the are small in size and therefor easy for a computer to handle. If you scan them at a higher resolutions the images will be larger and therefor more processing power and ram will be needed to handle them. There is a direct relation to the resolution of the scan and print quaility. You can experiment scanning them at 600dpi and see what it looks like printed. If it still looks bad try 1200 dpi and so on. Scaning them in at a high resolution and then resizing them won't give you better quaility over just scanning them in a your target dpi.
 

cullism

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I scanned the first four slides at 4800 and the second four at 2400. When I opened them in Photoshop all eight were the size of the original slides. What I then do is to reduce the resolution to 600 and resize the images to postcard size. This procedure issuccessful but time consuming. I will try scanning a slide at a lower resolution (600) and see what happens. I once read that one should scan slides at high resolution for the best result.

Thanks for your help.
 

fairnooks

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Make sure that when you are viewing them in Photoshop that the window scale says 100%. If a slide scanned at 4800 dpi and it doesn't run right off the screen when viewed at 100% then some other setting is not being factored in because a one inch slide scan would be 4800 pixels across on the screen and my largest screens are only 1920 pixels across. Even a half inch slide would still be 2400 pixels wide.

It is going to take the computer quite some time to process any change to a 2400 to 4800 dpi scan--there's a lot of info packed in there to change.

If the intent is to print then as a rough estimate use 300 dpi as the print resolution. That means if you want to print 5x7 and the slide is one inch on the long side (if there is a long side) then you would need 7x300 pixels or a scan dpi of 2100.

If you wanted to really stretch it and go for the 8x10 print size then you would need a scan dpi of 3000 (10x300), and maybe if you are going to be archiving these scans, that might be a resonable dpi to set for all the scans so you can save a high quality scan.

The higher you go, the more its going to tax your system, and you may be satisfied with a print resolution as low as 240 dpi, which can save some processing time.

The only thing you should not be doing for sure is resizing and changing resolutions unless its a copy and you just want it for viewing on screen or for emailing, where resolution is usually much less important.
 
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If you are archiving the images you want pretty much all the information on the slide transferred to the digital image. Otherwise you will have to regularly dig out the slide you want to work on if you decide to crop something out or make a larger print. The sweet spot for scanning slides and film seems to be around 3200 PPI on a good flatbed. Above 3200 you are getting very little image improvement for a lot of scanning time.

Your Photoshop problem is I think a lack of sufficient RAM. The speed at which Photoshop runs a filter or process is generally a function of processor speed as long as there is sufficient RAM. Once Photoshop runs out of RAM and starts using virtual memory things slow to a crawl on any computer. There are some things you can do to help, but you will eventually want more RAM.

Shut down everything else that is running.
Go through your startups and uncheck anything you don’t really need starting with the computer boot: http://www.pacs-portal.co.uk/startup_content.php
In the Photoshop preferences increase the RAM that Photoshop can use to around 80%. That is 80% of what is unused, so it won’t help a lot if you don’t clean out your startups and shut everything down before using Photoshop.

If you want to reduce the image for a particular output that is fine as long as you don’t overwrite the original high quality scan. Say you want to print a 4 X 6. The first thing in processing would be to set the crop tool to 4 X 6 and 300 PPI. With a number in the resolution box the image will be resampled, and in this case to a smaller file that will use less RAM. It is a bad idea IMO to regularly leave a set PPI in the resolution box.

If you are running out of RAM, the best bang for your buck in computer performance is another stick of RAM.
 
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