process for resizing prints

Discussion in 'Digital Darkroom' started by 15sunrises, Jun 16, 2010.

  1. I recently printed a bunch of A3 prints (42cm on the long side, about 18 inches). I'm using a 40D, so at 300dpi, the images needed to be slightly upscaled in order to fit the A3 size. In photoshop, I simply rescaled the images to 42cm on the long side and printed. While the prints looked quite good, and sharp, I'm wondering if this is the correct resizing process, or if somebody could help out in terms of how I could squeak out a bit more quality.
    Thanks again.
     
  2. Hi Dave: Yes you did it correctly. Sandy
     
  3. stb

    stb

    But why 300dpi? What printer do you use?
     
  4. Hi Stephane, I used an Epson R1900.
     
  5. stb

    stb

    OK. then use the following resolutions, depending on what print size you need: 180, 240, 360, 720. Use the one that needs the less resizing from your file.
     
  6. 180, 240, 360, 720​
    ???????????????????????
    The right PPI values are 360 or 720, depending on printer settings.
    For borderless prints the values may be slightly different.
     
  7. stb

    stb

    OK, the detailed situation is that for desktop Epson printers like the R1900 the native resolution is 720ppi. Sending a 360ppi file will produce a great, artefact-free print. Ditto for 180. 240 is an intermediate resolution that works very well too.
    The main point is that 300ppi is never the right resolution for an Epson printer. 300ppi comes from the first desktop laser printers 20 years ago and has sticked in people's mind since.
     
  8. OK.300 PPI is an old, incorrect, value. It has nothing to do with the human visual system resolution power.
    But for HP and Canon it's a good value, same as 360 for Epson.
    360=720/2
    300=600/2
     
  9. I can see no visual difference of 300 vs 360 at A3 size even with a 10x loupe on my Epson printer. Could be my eyes yes, but even Epson's book on printing which I have doesn't say you have to use multiples of 360.
     
  10. Differences are more noticeable in shots with a geometric pattern.
     
  11. Having a 300 ppi image looks about sharp to most humans at 1 foot; whether you want to believe this century old parameter is another story.
    It is incorrect to think that this well established rule is wrong; since human eyes are not getting better.
    The value of 300 ppi *is* based on about 1/4 century of actual printing in digital; it is an extension of pre digital rules of thumb.
    It is just a rule of thumb many of us have used in printing about forever
    By *rule of thumb* it means a starting point; NOT a fixed in stone number.
    If the image is naturally 8x10 inches at 300 ppi and one upsizes to 8x10 at 360 ppi often one cannot tell any difference but one makes a typical bloated file.
    Newcomers seem to thing that upsizing magically creates more details. Here in printing new customers seem to be always excited about upsizing; where in most all cases print A and B look them same.
    *****What ppi value a printer can "support" depends:
    (1) On the printer model;
    (2) its software settings;
    (3) the coarseness and absorbability of the type of paper/linen/mylar/vellum/cloth/canvas used.
    (4) The settings of the RIP if used.
    (5) Alignment of the heads
    (6) choice of subject matter. (line, geometric, pictorial, font style and size)
    There are materials so rough they only support 100 to 120 ppi; and 150 ppi is overkill; 300 ppi is an absurdity; 360 ppi is laughable.
    The 300 ppi number goes back before digital; it is twice the line screen (150) of a better printing. Newspapers are about 80 to 90; cheap flyers about 65; National Geographic about 170 line screen.
    Newcomers seem to be totally confused about rules of thumb;
    they are a starting point and not some rigid cast in stone number
    Some of us who grew up with slide rules use rules of thumb all the time; it is like the F16 rule for exposure.
    ****Using 300 ppi is a good starting point on most all copiers and printers ever made; this BOTHERS the lay and newcomers; who seek exact answers to a fuzzy problem.
    If an ACME 360 printer actually supports a 360 ppi image; upsizing an 8x10" image from 300 ppi to 360ppi often does nothing but make a bloated file. Thus folks confuse upsizing with what a printer will support.
    Here I have some old Epson printers that run their best at 300; thus the lay here saying to use 360 does not fit well with one of my several of my 36" color machines. Usage of 360 just delays the print coming out a tad; it adds no extra details; it frankly wastes time. Since time doesnt matter to many folks; you can do goofy things that waste time and money but add ZERO value. It is basically time goofing off; it adds zero value to a print but drives up costs-
    An ancient Novajet 36" inkjet here still used is a 300 dpi device; it supports about 150 to 175 ppi only; it is from 1993
    A Brand New Canon large format printer here is called a 1200 dpi device. They say "2,400 x 1,200 dpi (Max)" . Its default settings are 600dpi in its driver; and often a 300 to 500 ppi image all looks about the same. There is NO magical ppi value that it *wants* to see like others say an Epson needs a 360ppi image.
    Without mentioning any model; saying using ABC ppi for Epsons is downright goofy and misleading. It is like saying use XYZ transmission fluid on a Ford car; without mentioning what model. This lay dogma causes more even confusion.


    Just run some of your own tests on each printer. That is what us print shops do on each machine and RIP; you use the lay numbers web as a guide; since often folks repeat a bunch of garbage. Some of us have done this before the web existed; in 2400 modem BBS days
    It is sad now folks cannot experiment anymore and cannot understand the basics and how dogma is preached like it is cast in stone.
    300 ppi with digital prints is common as 2x4's and 12 guage wire in American homes. It is as common and SAE 30 or SAE 10W30 oil for cars; or using a 50mm lens on a 35mm slr.
    One can argue until the end of time what is the proper ppi for a printer; what oil to use in an unknown car.
    A common themes on photo.net for over a decade are:
    (1) upsizing
    (2) What ppi to use ; with often with no printer or type of paper mentioned
    (3) How big can I enlarge
    (4) How big of image do I need for a print; poster or billboard (with never any mention of viewing distance.)
    (5) arguments about the 4 century old 72 number
    (6) film versus digital arguments
    (7) my flatbed is not a zillion dpi device
    What matters is works best for you. Here in printing big wall maps a 400 ppi image is used.
    Since the public is so fixated and confused about pixels; many folks inputs that are 300 to 400 are already bloated ; since they are already upsized. This further clouds the issue. One has a crappy input of useless pixels anyway.
    ******The public often confuses what a printer can support under best case conditions with how to upsize their sunset image that holds little if any details.
    Thus if an un-upsized Sunset image is about 24x36" at 100 ppi; many of us upsize it somewhat; but not way too much.
    If my new Canon can support a 600 ppi image on great paper; upsizing the 24x36" 100ppi image to 600ppi is over the top; it really looks no better than 500, 400, 360 or even 300. If one CANNOT see any difference in a print; you have gone too far.
    In this example 1 pixel becomes 9 with an upsize to 300 ppi; and 1 pixel becomes 13 with an upsize to 360ppi.
    A mile upsize makes the image look better; IF one gets close. If one prints samples at 24x36" at 300, 360, 400, 500 and 600ppi and they all look the same under a loupe/glass; it doesnt matter anymore.
     
  12. Having a 300 ppi image looks about sharp to most humans at 1 foot; whether you want to believe this century old parameter is another story.
    It is incorrect to think that this well established rule is wrong; since human eyes are not getting better.​
    What you "see" are DPI, not PPI.
    For contone printers DPI value = PPI value, but another time you "see" DPI, not PPI.
    For inkjet printers DPI >> PPI .
    DPI values are larger as printers lay down many dots to "simulate" the original pixel color. This is dithering or error diffusion.
    PPI and DPI values are predefined from the printer maker . These values are picked up from the driver as you set the printing preferences.
    When you fix the print preferences the PPI value and the DPI value are fixed.
    There is no way to change them.
    If you send an image with a different PPI value, the driver resamples.
    The sentence "I print at 300 PPI (or worse DPI)" is completely wrong.
    You print at PPI/DPI values selected from the printer driver.
     

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