Film scan: More Resolution = More Shadow Details?

[steven_woody]

i send film to lab and have them scan in, the lab charge by per MB of final file

size. because the picutre will be used only for web publish, so i think i dont

need so many resolution hence get only a small file. but i found people said,

on the net, that more resolution implies more details in the final picture, so i

want to ask whether or not this is true, and i hope i get some reasoning.

 

thank you.

 

-

woody

[garry_anderson3]

More resolution doesn't equal more shadow details. More bit depth (ie 16 bit)may give you more shadow detail, but it depends on the type of film you are scanning, the exposure and the quality of your scanner. Most people agree that in the real world the best you can hope for is the equivalent of 14 bit of depth under ideal conditions. You can of course overlay a number of exposures to increase the apparent bit depth.

 

More resolution give you more pixels to play with, thus you can print a bigger image. Again the final result is determined by the type of film and the quality of your scanner.

 

With film the higher the resolution, the greater the detail in your image upto a given point, generally around 2700dpi, then the law of diminishing returns kicks in. ie a 5400dpi scan does not give twice the resolution of a 2700 dpi scan.

 

Scanning artifacts do decrease with an increase of dpi, but these rarely seem to impact a final image.

 

For web use a small resolution is all you need. Computer monitors are only 72 pixels per inch.

[James G. Dainis]

Resolution with digital means image size. A film scan of 2700DPI would give you about a 3800 x 2500 image. That is 3800 pixels wide by 2500 pixels high. On the average monitor which is about 1024 pixels wide, that image would be over three screens wide. People would have to scroll sideways and down to see the whole thing. You don't want it that big. You would have to reduce it down to about 500 x 325 to be about 1/2 a monitor screen wide.

 

3800 times 2500 = 9,500,000 pixels = 9.5 megapixels (MP) = 28.5 MB

 

500 times 325 = 162,500 pixels = 0.16 megapixels (MP) = 0.48 MB

 

Why pay for all the MB if you are not going to use it?

[steven_woody]

thank you for the replies.

 

now i think, to get a 800x800 picture for web publishing or sharing with friends, i problely need 1600x1600 pixels ( i usually downsample a scan image with a factor of 2 to improve it's S/N ), so, for my 6x6 negative, the scaner resolution i need is about 1600/2.54 = 711DPI.

 

-

woody

[bill_tuthill]

Despite what other respondents have replied, some labs provide

much worse quality (than would be expected by simple downsampling)

in low-res scans than in medium- or high-res scans.

 

Furthermore, most downsampling algorithms have the effect of

increasing contrast. So I believe you should trust your eyes.

By the way, Lanczos (free in Irfanview) is, for most images,

a better downsampling method than anything in Photoshop.

[shay collings]

Labs using Fujifilm Frontiers will offer (well maybe not offer but be capable of) three types of film to CD resolution

 

- 1Base JPEG = 640x480 'email' quality scan

- 4Base JPEG = 1840x1232 'roughly about 3-4 MP I think'

- 16Base JPEG = 3000x2000 'about 9MP' - This can be expensive because it can take 10-20mins to scan the film.

 

Anyone who says that the is a noticeable difference between them is wrong in my opinion (I work on a frontier 40hrs a week). The only difference between the film and the digital file is caused by the person processing it. Colour, Density (Brightness), frame positioning and shadow/highlight correction are all done by the Photolab Tech as the film is scanned. If you are really concerned about colour, shadows etc. Ask for them to scan the film to CD with NO colour corrections, trust me they won't mind :-)

[shay collings]

Oh and BTW I wouldn't waste time with a lab that charges by the MB. Every lab I have ever worked in or had knowledge of charges by the exposure length of the film eg. where I work at present

 

- 4Base JPEG - 24exposure = NZD$10.00

 

Also if you are wanting slides to CD after processing then ask for them to be left uncut or cut into normal sleeve. Having mounted slides means the lab has to change all their film scanner masks to a manual (very slow) slide mask, which in most labs will increase the price.

[kelly_flanigan1]

Charging by the megabyte of scan is actually ancient and goes back before Photoshop was born. Once a megabyte of drum scan was several dollars per megabyte then it went to 1 buck then lower. Since there are many different scanners, bit depths and formats this older method of pricing is not used as much. Its basis it to charge for a scan that takes longer. An old 4x5" drum scan at 600 pixels per inch cost less than one done at a 120oo setting; and took less time to scan. Still the older model was usually more of Y=MX + B model; with a fixed cost of setting up the scan on the drum and then a XYZ dollar/megabtye of scan cost.