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Quality of scans of slides

4 Aug 2011 1:09PM
Bit of an odd one.

My dad has given me hundreds of slides that he took of the family as kids which haven't been viewed for nearly 30 years and I am starting the process of scanning them all in order to try to preserve them and make it easier for the family to view and get prints now that we live all over the world.

To do this I bought the Plustek 7600i SE dedicated slide/film scanner and so far I've only scanned around 15 slides but I'm having doubts over the results I'm getting.

The scanner came with the Silverfast SE 6.6 software but to be honest I found it not very intuitive so as I already own the program Vuescan I switched to using that.

I'm scanning at 7600 dpi and initially had Vuescan set to 48bit and to output at Scan size (i.e. not enlarging it). Now I should say at this stage that the slides I've started scanning are all shot indoors using flash and so many of them have darker backgrounds where the light from the flash has fallen away. Also whilst my dad's camera was a reasonable SLR the lenses he had weren't particularly fast or sharp.

When I've scanned these slides they result in a TIFF file of around 160MB with the dimensions of around 7600x6500 and when viewed so I can see the entire photo on screen they look great. However when I zoom in I start to notice a lack of detail primarily in the background where instead of a more natural gradient to the tones of the shadow I'm seeing more of a posterisation/blocky effect. There is also quite a lot of noise/grain which may be contributing to the blocky effect. This seems to affect any area that is under exposed but even faces that are correctly exposed aren't as sharp as I'd have expected but maybe that's down to the lens, shutter speed and film grain?

If I set Vuescan to 64bit then the quality does improve but it's still not perfect. Is that to be expected, am I expecting too much or are the settings I'm using wrong?

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rambler Plus
9 956 17 England
4 Aug 2011 1:23PM
I am not great on technology but I will start the debate by suggesting that what you are seeing is pixelation, a drawback of digital images. Also if the photos are to be viewed on a standard computer or TV screen all you need is a resolution of 1064x768.

mikehit 8 8.0k 13 United Kingdom
4 Aug 2011 1:34PM
When you say you 'zoom in', what magnificatino are you looking at? If it is 100% then you are looking at an image 7600 wide which is equivalent to an image about 6 feet across which for a 35mm transparency will be amazing it it is sharp. I used to worry about the apparent sharpness until I realised that on my 19" screen, full viwe in PS Elements is an image the same size as printing at A4, which is my common large print size so if it looks good on screen it will be OK in print. Don't be seduced by 'zooming in'. Given that people who are vastly more experienced than me will not print over 12x8 from 35mm transparency so view your slides in the same way.
Also, if I recall correctly the Plustek does not have autofocus so if the slide has 'popped' or moves in the holder it may not be in the best position for maximum sharpness. And that all presumes the original scan is sharp to begin with.

As for the shadows, I am not surprised that you are seeing posterisation effects but this may well be because you are zooming in to unrealistic levels and the program has to create transitoin somewhere. And the signal-to-noise will reduce because there is little colour there.
But a scan, just like a digital print, needs post-processing work (including sharpening) to get maximum viewing quality. Have you used scan preview and played around with the profiles? This may help to get ready-to-view images with minimal work afterwards.

Regarding resolution it is almost pointless scanning at 7600 DPI because you will probably find that the scan maxes out at about 3,000 or even less. Remember that after a point all you are doing is getting a better scan of the film grain and you are increasing file size to no real benefit.

Overall, I think you arexpecting too much. I suggest you send a few slides to One Vision Imaging and get them to scan at their best quality - at least then you will be able to see what is possible when professionals use the best equipment.
4 Aug 2011 10:10PM
By zooming I mean that this effect is noticeable when viewed at just 33%. What I can't quite get my head around is that Photoshop reports the image to be 7392px x 6984px and at 7600dpi it as a document size of 2.61cm x 2.46cm. Dropping the resolution to 300dpi makes the document size 62.59cm x 59.13cm but obviously it still looks the same. So would I be right in thinking that because the original format is so small yet the scan resolution is so high that actually the software/scanner is having to interpolate to create the file of the size it does and that therefore it is this interpolation that is causing the posterisation type effect I'm seeing.

Assuming that is correct what resolution would people recommend I use bearing in mind that the point of scanning them is to preserve them i.e. for archive purposes and from these 'high res masters' prints of many different size could be made as well as smaller versions for screen viewing?
4 Aug 2011 10:23PM
Hmm, well I've tried dropping the resolution down to just 1800dpi and it's identical just smaller. Maybe this is film grain as it would have been a slow film he used as it was all shot indoors in low light?
User_Removed 14 3.3k 4 United Kingdom
4 Aug 2011 10:47PM
Are you sure your scanner is actually scanning at those high rates? Above 600 many just interpolate.

I scanned a load of my dad's old slides, the higher res scans just showed up the imperfections all the more. I knew they'd only ever be shared over the internet and viewed on monitors so I scanned them at a lower res so they came out at no more than 1600 pixels wide. This had several benefits:

1) Scanning times were much faster

2) Files were small

3) Photoshopping was easy as the files didn't use up too much memory
stomp 16 203 England
5 Aug 2011 4:18AM
A 35mm slide scanned at 7600 would give an image file with dimensions of 10,640 x 7220 (1.4" x 7600)x(.95"x7600) so where you are getting an image sized 7392px x 6984px I do not know because this is not even the correct aspect ratio for 35mm film (24mm x 36mm) which is 2 - 3.

To print an image on a printer at a print resolution of 300dpi would give you an print 3 feet long.

The same image displayed on your monitor at 100% @ say 96dpi would give you a view of a section of the image equivalent to 12 inches of the length of the mentioned printed image.

By zooming in so close you are bound to see more film grain and other artefacts.

Also, the days of scanners only being able to scan at 600dpi without interpolating are well gone and now the preserve of very old scanners.

My advice would be to scan to provide a file large enough to satisfy the biggest print you are likely to produce. I would be tempted to scan at half the max resolution of the scanner in 48bit and save as a raw file in Vuescan

5 Aug 2011 10:46AM
Thanks all for your comments. To address them in turn

The scanner I bought is the Plustek 7600i SE which is a dedicated film/slide scanner that has rave reviews and seems to be one of the best film scanners you can buy under 5K considering it's price tag of 250 and yes it doesn't scan at 7600dpi but actually 7200dpi (a typo by me)

The reason I decided to scan at 7600dpi was largely based on this review of the scanner . In other reviews on this site it suggested that in order to achieve the best from your slides you needed a scanner that could achieve an effective resolution of over 3000ppi which few scanners under 300 can achieve. The Plustek, according to their test results, achieved an effective resolution of 3250ppi but this is achieved when scanning at 7200dpi.

That said this review of the scanner [link=Here]http://www.imaging-resource.com/SCAN/PLTK7600/7600.HTM
demonstrates more what I'm seeing in their samples where I'm not seeing any additional detail when scanning at 7200dpi compared to 1800dpi just that the amount of detail that is being captured doesn't look right to me.

The aspect ratio of my scans is something that occured to me too. I had assumed my dad used a 35mm SLR as that was the camera I remember him having but these slides are definitely more of a square format and I do seem to remember him saying that he used a different camera before he bought the SLR's so perhaps that explains it? All I know is that the slides have Kodachrome on the mount so perhaps he was using 126 film and not 35mm as that's the aspect ratio I'm seeing and Kodak did make that stock in 126 size. If it is 126 stock could that explain the 'issues' I'm seeing i.e. did/does 126 film capture (and/or the camera he used) the amount of detail that say 35mm film and a SLR could?

Ultimately he wasn't a 'photographer' and these aren't works of art, they are just family photos but have huge sentimental value and I just want to preserve them as best I can as they are the only record we have of those times.
User_Removed 14 3.3k 4 United Kingdom
5 Aug 2011 11:24AM
Hadn't realised your Plustek was a decent scanner, for some reason the brand made me think of a cheapie hence my view that it might interpolate higher resolutions.

I agree with Steve that there's not much point scanning bigger than you intend printing. (Unless you plan on doing a lot of cropping beforehand?).

I can empathise with your view that you want to do things at archive quality, it's a one-time job.

I lied about what I'd done with my dad's just to save a long story which I'll now tell.

There are about 400 slides in my dad's loft which I intended to scan. I started procrastinating on the best way to do it. Reading up on fancy Nikon scanners, checking for bargain high-end slide scanners on eBay, looking into scanning services etc etc. Never actually getting round to it.

My brother-in-law (who is not even blood grrr) bought some 90 USB tat out of the Sunday Post Magazine, spent a weekend with the box of slides and scanned them all. He then made copies for all of the family and everyone was totally delighted. Including me. There were the Christmas Days, the Butlins and Pontins holidays, my mam when she was my age (who died 18 months ago), dozens and dozens of childhood memories etc etc etc.


You can see from the EXIF data that it wasn't a sophisticated unit. I've never done a "proper" scan and probably never will. The images are fine and have been shared with family and friends far and wide, in the end that's what matters so don't get too hung up technical perfection.
5 Aug 2011 9:27PM
Hmm, well I've just done a scan of a more recent slide that definitely was shot on 35mm and in daylight so presumably using a faster film too and it is better exposed.

Scanning as before using Vuescan at 7200dpi produced a better result, so perhaps it is the difference between film stocks, film speeds and exposure. However there was still a bit of this posterisation effect in a couple of spots where there were shadows.

I then decided to do scan the same slide using SliverFast SE again at 7200dpi. The difference was very noticeable. There was no sign of any posterisation at all and looked a lot better so it looks like it could have been Vuescan that was causing the problem. I'll need to rescan one of the indoor/darker photos on the 126 film stock to be sure but this looks promising. I need to learn how to use Silverfast better though as I'm very slow at it and find the interface less than intuitive and a bit clunky but if these results continue it'll be worth it!

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