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Standard User Brunel
(experienced) Wed 02-Feb-11 10:08:33
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Slide scanning advice


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I am using an Epson 2580 photo, to scan 35mm slides.

I also have an ancient Nikon LS20.

I found the Nikon somewhat lacking in handling dark areas.

The Epson produces a much better scan using the Epson software, however the images appear slightly soft.

I am scanning at the largest resolution 3000x 2000 not looking for absolute perfection, so I am saving in jpg format.

What is the optimum DPI setting I should use for normal screen display? I have the option of 96 up to 2400.

I have tried various numbers, but I cannot see any difference.

Edited by Brunel (Wed 02-Feb-11 10:09:25)

Standard User FelixTCat
(committed) Wed 02-Feb-11 10:43:30
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Re: Slide scanning advice


[re: Brunel] [link to this post]
 
Hi Brunel,

If all you require is normal screen display, then you only require a low resolution and 96 dpi is probably adequate. You can check this from your monitor by measuring its size and comparing that to its resolution. As an example, I have a 22" screen at 1920x1080. The screen is 18.8" by 10.5" visible size. Thus there are 102.12 dpi horizontally and 102.85 dpi vertically.

If you want the option to print, then scan at 300 dpi, which is the resolution of most printers.

Personally, I would scan at at least 300 dpi - it doesn't take much longer and the additional disk space isn't really relevant in these days of multi-gigabyte hard drives.

Regards,

Felix
Standard User Brunel
(experienced) Wed 02-Feb-11 10:45:50
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Re: Slide scanning advice


[re: FelixTCat] [link to this post]
 
Thanks, I will try that.


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Standard User ian72
(knowledge is power) Wed 02-Feb-11 13:39:04
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Re: Slide scanning advice


[re: FelixTCat] [link to this post]
 
Surely the DPI in this case is not based on the screensize?

If I want to display a scan at full screen resolution (and no more) then I would need that image to be 1920x1080 (using your screen res as an example). It is irrelevant whether the screen is 15" or 50" if the resolution is the same.

So, what you need to do when scanning is try to get up to that sort of image size. If the image is a 9"x5" photo then you would need 1920/9 and 1080/5 - 213 dpi in the horizontavs 216 dpi in the vertical - so 216dpi.

However, if we are talking slides then a slide is much smaller and so would require a far higher capture dpi. Assuming a slide is approx 1"x1" that would require a dpi of 1920 to capture the horizontal width (this is just an example as I don't have a slide/negative here to measure).

So, the DPI is only relevant to the capture compared to the target resolution.
Standard User MHC
(legend) Thu 03-Feb-11 09:29:36
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Re: Slide scanning advice


[re: Brunel] [link to this post]
 
2400 - as you are saving as JPG, choose the highest quality setting that you can. If you then need to send a small image you can always process down in resolution or quality but never up. I always use 4800 or 9600 for mine unless it is special one off that just needs a quick scan and no fine detail when I will drop to around 1200. The only downside of you going to a 2400 is that it will take a little longer to scan and the size on disk will be greater.

As an experiment, try scanning an image at 2400 and saving as high quality. Then, without moving the slide, scan at 96 and save as a low quality JPG.

Load both images side by side and zoom in to a fairly detailed area on both and then compare. You will start to see pixelation and loss of clarity on the 96 dpi scan.





~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


M H C


taurus excreta cerebrum vincit
Standard User Brunel
(experienced) Thu 03-Feb-11 10:43:34
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Re: Slide scanning advice


[re: MHC] [link to this post]
 
I am scanning at the largest size possible.

35mm film is 36mmx24mm an aspect ratio of 3:2, I am using 3000x 2000 pixels as the size.

I can set the resolution anywhere between 96 DPI up to 2400 DPI.

It is recommended to use 300 DPI if the scan is to be printed.

It is this DPI that is confusing me.
Standard User ian72
(knowledge is power) Fri 04-Feb-11 08:22:54
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Re: Slide scanning advice


[re: Brunel] [link to this post]
 
See my explanation above. 300dpi is the output of a printer. But, if you were printing an A4 page they are approx 8" by 11" then you would need an image that is 2400 x 3300 pixels to get a native print quality.

The dpi is always relevant for the output. Once you know what you need to output then you need to ensure the capture dpi matches (so for 36x24mm film to print at A4 you would need a dpi of over 3000 in the capture as you are effectively blowing up the image by a factor of 10).
Standard User Brunel
(experienced) Fri 04-Feb-11 10:39:17
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Re: Slide scanning advice


[re: ian72] [link to this post]
 
Thanks, I am saving for screen use only.

Using the dedicated Epson software it appears that as they say "size matters"

In my case large pixel size and 96 DPI gives a good result.

No doubt if I used a dedicated read expensive slide scanner, the results would be even better.
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