Resolution, Images size and capturing detail

Discussion in 'Digital Darkroom' started by cliffk, Sep 23, 2010.

  1. I apologize if this post is amateurish, but I'm working hard to better understand scanning resolution and its actual impact on image quality, clarity and final print size.
    Let's start with what I do understand: I am using an Epson V700 scanner and I mostly scan medium format negatives, I have the option to pick from several resolutions: 3200, 4800, 6400 and 9600 dpi. I understand that if I'm using a standard printing resolution of 300dpi., (although I do have some labs producing images requesting the image file be set at 400dpi.), that I want to create a file size, or use a scanning resolution that will provide the pixel dimension for the desired final image size.
    So if I wish to print a 10x10 inch image, at 400 dpi, then I need to scan my medium format negative at a resolution or pixel dimension that will give me a minimum of 4000x4000 dpi width and height.
    My goal is scanning quality and capturing as much detail or information as my scanner can. I use Nikon's View NX as my viewing program before I import them into my photo editing program. One feature of the Nikon VIEW NX is a resizing and converting function. I use this on occasion to resize, mostly downsize a file to the appropriate size. Sometimes, I'll batch convert a large body of work to a smaller size, say down to 5mb's, as opposed to the 180mb file that results from a scan of say a 6400dpi resolution setting, for quick view purposes on another device.
    Here is the question: if I take my scan that was scanned at a resolution of say 6400 or 9600dpi, and resize it to a dimension of 4000x4000 dpi for printing a 10x10 inch print (for a printing resolution of 400dpi), has the larger scanning resolution captured more information or detail than if I had scanned at 3200 dpi which would have initially created an original file of say 4000x4000 dpi's? What is the correlation between scanning resolution and image dimension in terms of capturing detail? Does scanning at 6400dpi gather more image information and detail than scanning at 4800dpi? Is the scanner collecting more detail and information for the given inch? Does it even matter?
    On another note, should somebody be really familiar with the Epson V700, in the configuration settings I can select 1, 3, or 5 pixels for the eyedropper and densitometer functions. For best results what is the desired setting? It amazes me, I have downloaded all the manuals and their webbased instructions, it tells you what everything is but not necessarily how to use it best?
  2. The best practice is to scan the film at the highest practical resolution at the film size. Theoretically, the higher the resolution, the more detail you can capture. For a V700 scanner, the nominal value (optical) is 4800 ppi, but in practice, the resolution is closer to 2200 ppi. If you scan higher than 2200 ppi, you increase the file size dramatically but add little or no more detail.
    The trick can be determining the actual resolution, since most scanning software looks at the output (print) size for the resolution. You can approach this in at least two directions - (1) set the output size equal the film size, or (2) calculate the true resolution from the ratio between the output and film size. Once you have the image file, you can crop and resize copies of that file for a particular purpose, and resample up or down as necessary.
  3. As Edward has advised, he seems to be knowledgeable of the more accurate and true rating of your scanner model. Please be further advised, 300 dpi IS NOT an accurate or true standard of print resolution nowadays. (Brain Lawler proved this 20 years ago to digital image-makers.) Therefore, you first find what the true print resolution by imaging black & white line pair frequencies and scanning like test patterns from your scanner or digital camera. The line pairs you can create in Photoshop to print, the line pairs to scan may be difficult to find but there should be resolution films chip still available for purchase if you care to be critical.
    "300 dpi" has always been misleading. It was the printer's line screen that mattered. 133 lpi, 150 lpi, etc., for example. Thus a reason a modern printer manufacturer may say the machine resolution is 360 dpi but files sent at 180 ppi from Photoshop look great! (The machine is actually delivering that 180 ppi resolution pixel-for-pixel.)
  4. Unless you know the actual printer model; the paper used; you have no exact answer in the amount of details it can hold.
    Also be advised that having a 300 pixel per inch image at the target size is what most all editors want; and this goes back 1/4 century. Having more is better; they can crop and enlarge.
    None of this is anything new; a better publication holds more details ; it was true 100, 200, 300 years ago too.
    In commercial printing; line work often can hold more details than CMYK dots.
    There are also office box store photo printers folks buy that really can support 300 ppi on a good day; sometimes 250 looks just as good and 300 holds no more details.
    Having an image that is at least 300 pixels per inch for quality printing is 1/4 century old. If you say it is a missnomer; or misleading an editor is going to place you in the corner.! :) One editor I have worked with since 1988 is TOTALLED annoyed with the worsening of the pubic's inputs; so much that I am a filter for several of his projects. If the images are say 5x7 inches and he/I want at least 400ppi;that means 2000 by 2800 GOOD pixels; not upsized stuff.
    asking for "300dpi" for a print is not misleading; it has been asked for decades; in fact is an industry standard since one it is twice the line screen of say National Geographic.
    If you tell an editor that "300 dpi is missleading" you get earmarked.
    it is like if you tell Verizion there is no such thing as a cellphone or minutes.
    Unless you know the actual printer model and paper; there is really no exact answer to how many ppi/dpi it can support. A super fine printer cannot print fine details on a bathtowel or kraft bag; or that rough canvas fine art folks love; the paper itself bleeds or is too rough.
    If you editor is the daily newspaper; its line screen is often about 85; a 170 to 200 pixel per inch image is fine; so is a 300 ; 400 etc. You could have a newspaper advert that is 2x3 inchess and send them a 2 by 3 image at 1000 ppi or 300 ppi and it will come out the same; it is only a 85 line screen.
    If I take my 1200 dpi large format printer; for line work on can have an image at 600 ppi as an input; for pictoral maybe 400 to 500; if one has glossy papers. With glossy paper that has less coating; one cannot see any difference between a 300 and a 350 ppi image/
    None of this is anything new; if one tried to print a bible 200 years ago with tiny type and poor paper; the type bled so the letters would merge.
    Here I run a service bureau; 300 dpi has never really been misleading. It is a very common goal; that we often do NOT even get. If "300 dpi is misleading" then so is a bull float or concrete truck to a main pouring a slab.
    BEYOND 300 ppi/dpi at the print size one may or may not get more details; one has the paper to consider; ie bleed in offset and inkjet. Not all the ink dries instantly; it spreads. The dots get larger; ie what has been called dot gain for the last 70 years.
    A practical scan resolution setting of a flatbed is say 2400 dpi. This means with a 2x2" actual scan area one gets 4800 by 4800 pixels in photoshop. For clarity; you see a 2x2 inch image marked as 2400 pixels per inch in photoshop.
    If an editor demands at least a 300 dpi/ppi image; this means you can enlarge 8 times. ie 2400/300=EIGHT.
    Thus in photoshop if you do NOT resample; you get a 16x16 image at 300ppi.
    A 300 ppi image at the actual print size is a great starting point. It is also wise to understand this; if you ever deal with an editor. Its is as common as a 2x4 to a carpenter.
    If you change that image to be 13.33 x13.33 at 360 ppi; or 12x12 at 400 ppi; you may or may not loose details; it depends on the paper quality; and printer class; and the print head alignment.
    Even if the 12x12 inch print at 400 ppi has the same details as the 16x16 print at 300 ppi; you wlll have to get closer than a foot so see them in the 12x12 one.

    Notice I purposely used 2400 dpi for scanning to be conservative; and the common 300 ppi number for the image sent to the print. This means a 8 x enlargement. There are foplks who say their flatbed is more like a 1800 dpi device; thus this means a 6x enlargement. If you use a 1800 scan and a 360 print this is only a 5x enlargement; ie a 10x10" image from 2x2 MF with a slight crop.
    Thus as a practical matter; a 5 to 8X enlargement can be done with a flatbed.

    Once one introduces viewing distance; the 300 ppi criteria can be uses by ratioing.

    A print done with a 300 ppi image looked at 1 foot away looks good to most folks; thus

    A print done with a 30 ppi image looked at 10 feet away looks good to most folks; thus

    A print done with a 3 ppi image looked at 100 foot away looks good to most folks; thus

    A print done with a 1 ppi image looked at 300 foot away looks good to most folks

    An 12x48 foot image for billboard in a cowpasture by an interstate can have its closest viewer be 300 feet away; this means one really only needs a 1 pixel per inch image; ie 144 by 576 pixels; a screen capture is overkill.

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