Epson Perfection V500 Resolution vs. Target Size

[martin.mintal]

Hi guys,
I just aquired the V500 Epson-Scanner, but - unfortunately - I don't really understand the difference between resolution (dpi) and "target size" (if some of you use the epson scanner software, you will know).

Now, dpi means the number of "dots" per inch, which means more dpi results in bigger pictures. For example when using 4800dpi, I get a really large picture.

Now, when I print a 4800dpi file on a A4 sheet of paper it will probably have a higher quality (resolution) than a 600dpi file, right ?

My questions:
1. What happens, when the bigger file is printed on a size o paper similar to the original size of a 600dpi file, for example ? Is the quality difference really visible ? So in short: Does it make any sense to scan at high dpi when printing small photographs ?

2. When the "target size" is original (in my scanner software) and I increase the dpi/resolution, the file gets bigger and bigger. However, when I define a target size like 1024x768, the file always has the same size (1024x768) but more dpi (in windows-properties of the file). However, I cannot see any difference between a 900dpi and a 4800dpi 1024x768 file - can somebody of you explain this to me ?

3. Funny thing is, all my Canon 5D files have a high resolution (for example 12MB = 4368x2912), but only 72dpi ????? :bang:

4. Do I always have to scan my 35mm negatives/slides at highest possible dpi, like 12800 or 6400 when I only wanna watch them on my monitor (22´) and only make max. 20x30 prints or so ? I mean, does it make any sense to scan at 6400-12800 ? Because the pictures are bigger but when you watch them on a 22´screen, you won't see any real difference between a let's say 1200dpi and a 6400dpi scan, am I right ?

So huge dpi only makes sense when printing large pictures ?

This is really confusing, because there is obviously a difference between RESOLUTION (like 1280x1024) and dpi...

There are actually 3 variables:
- the size of the original document/negative/whatever
- dpi use use
- target size (resolution of the output like 1024x768 or 2048xetc.)

Thank You

Martin

 

[martin.mintal]

I also wanted to add...

I also wanted to add...

the Epson V500 is a really good scanner - I already made some test scans from some of my 35mm negatives - at 1200dpi you get very nice pictures suitable for web use.

I was really afraid, because many testers stated that the V500 is inferior to the for example Nikon Coolscan - I mean, this is probably true, but for "normal" usage (for watching you pictures on your screen and for normal prints like smaller than A4) the scanner is really more than adequate.

The Digital Ice technology works like a wonder

 

[historicist]

OK, when the scanner is scanning, more dpi just means more resolution. Just like a 12 megapixel dslr has more resolution than a 6 megapixel dslr, but exactly the same size sensor, when you scan a 35mm frame on your v500 the piece of film stays the same size but you record more pixels, i.e. more detail from it.

DPI is a measure of how many dots there are in every inch of the physical item, i.e. the film you are scanning or the print you make it into at the end - it does mean the same thing as resolution, at least when you are scanning in. If I can resolve 4800 dots for every inch of my film, clearly I have greater resolution than if I can resolve the same size original with 1200dpi. But an image file, unlike paper or film etc. has no dimensions so it is not relevant at all to a file. This is why your canon simply says 72dpi, simply because by convention computer monitors have 72dpi, and this is why there is absolutely no difference between 1024x768 at 10000dpi or at 10dpi in terms of the file. If you were to print them pne would be a lot smaller than the other though 😉

it might be worth reading this: http://en.wikipedia.org/wiki/Dots_per_inch

OK, so your questions:

1. No, but it might save you having to rescan the film if you need it in the future at a higher res.

2. When target size is 'original', for every inch of the target the scanner will save x dots (where x is your dpi) in the file. So the file resolution will be ((dpi x horizontal size) x (dpi x vertical size)). Setting the target size to something other than original is basically just a convenience for those who know they need specific size output for web galleries or whatever, it saves them having to resize the image in photoshop. The scanner software just automatically resizes ((dpi x horizontal size) x (dpi x vertical size)) to 1024x768 etc. Obviously, if this means resizing 4200x3000 to 1024x768, it just means you have wasted your time, as all the detail in the slow, hi dpi scan is thrown away. Think about target size and dpi in the scanner settings as different ways of acheiving the same thing ( a particular resolution file) than independant variables.

3. All digital cameras give 72dpi as a convention, as above it doesn't really mean anything.

4. No, there is no need to scan in a high dpi if you will only use the scans for viewing on your screen or small prints. The only advantage to scanning in at a high dpi in this situation is that you don't have to rescan if you want to print a massive file, heavily crop an image, etc. etc.

By the way, you should be aware that the resolution your scanner is physically capable of is less than the maximum available in the scanning software. The Epson V500 is physically capable of roughl 3000dpi. So there is no point whatsoever in scanning at higher than this resolutuion, for whatever purpose - you will just get bigger files but no more detail

 

[martin.mintal]

Hi historicist,
thank you very much for your detailed answer. You helped me a lot ! Now I finally understand....I will simply scan at 3200dpi or smaller then...