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Resizing for PDI - Why...?

Discussion in 'Digital Image Editing & Printing' started by dangie, Sep 18, 2017.

  1. dangie

    dangie Senior Knobhead

    At our camera club's Practical Evening in a couple of weeks time I am demonstrating resizing images to be used in PDI competitions. With this I have no problem with at all.

    However, please forgive to what may seem a very basic question, but what are the reasons WHY we need to resize images for PDI competitions? Can a projector not project a full sized image eg 4000x3000. Would the projector not project it at its native resolution? I appreciate that by resizing down to say 1400x1050 you are reducing the file size considerably, but is this the only reason?

    Apologies if this seems obvious, but it's often the obvious that you miss.
  2. Andrew Flannigan

    Andrew Flannigan Well-Known Member

  3. dangie

    dangie Senior Knobhead

    Hello Andrew
    Thanks for the reply. I had already seen that one. In fact I've looked at many other camera club's write ups. Unfortunately they all describe 'how' to resize', I want to know 'why' to resize

    As it says on your attached link:
    "Modern digital cameras produce large images, in pixel dimensions the D300 produces images at 4352 x 2868. If you want to submit such an image to a PDI competition or make an Audio Visual you will have to make each smaller."

    This is the bit I'm not understanding. I know we have to make them smaller, but not why we have to make them smaller?

    Thanks again.
  4. Fishboy

    Fishboy Well-Known Member

    I don't know the definitive answer to this - but I've got a theory based on things I've read in other threads on the forum.

    I believe that you're absolutely right in that some software (like the Windows photo viewer) will automatically re-size an image to fit on the screen, however not all photo viewing software will apply the correct colour profiles from the original image.

    Perhaps the re-sizing is required because some software that does apply the correct colour profile doesn't automatically re-size images to the screen?

    Then again, perhaps it's all down to the size of the files that would have to be dealt with otherwise?

    Cheers, Jeff
  5. EightBitTony

    EightBitTony Well-Known Member

    Most projectors are still operating at non-UHD resolutions, and as such, images larger than the native display resolution will be 'resized' when projected. Depending on the size of the original image, that resizing will vary greatly between different images. Rather than allowing the resizing (and subsequent introduction of artefacts, or loss of sharpness) by the display card or projector, it's better for all the photographers to resize (and then properly sharpen) their own images in advance, so that it's a totally level playing field.

    One consequence is that you don't get multiple photographers complaining that their images (delivered at 3000 pixels wide, for example) were resized badly by the computer / projector / whatever and hence didn't display as well as they might have.

    This is even worse if the projector isn't in the same aspect ratio as the original image, so forcing everyone to resize based on the longest edge, solves that too.

    Remember, 24mp images are big, and you can't view them natively even on a 4k monitor.

    HD (1080p) = 1920x1080 = ~2MP
    Ultra HD. 4K UHD = 3840×2160 = ~8MP
    8K UHD = 7680×4320 = ~33MP

    4K projectors are upwards of £2k each, 8K projectors are upwards of £11k each.

    NB: I've never entered a competition, so I'm guessing.

    Other likely reasons,
    • the rules were written when projectors were even older and even worse, and when software resizing of images was even more terrible.
    • the rules are an extension of asking competitors to submit prints in the same size to ensure a level playing field.
    • the rules haven't evolved as projectors and computers have improved their resolutions, but are probably still valid anyway (until 8K UHD, although even then 40MP+ camera images will still be resized).
    Last edited: Sep 18, 2017
    Craig20264 likes this.
  6. dangie

    dangie Senior Knobhead

    Thanks Tony
    I think I'll base my explanation your first two paragraphs. They seem pretty feasible to me.
  7. PeteRob

    PeteRob Well-Known Member

    I guess not. It sounds like projectors just improved to 1400 x 1050 which seems astounding. While I have never broadcast a photographic slide show connecting computer to external projectors for powerpoint presentations has always been a compromise, made worse by huge resolution laptop screens. It makes sense to size images precisely for the dislay format rather than relying on the computer to make them fit. You get the result you intended.
  8. beatnik69

    beatnik69 Well-Known Member

    Until recently all our PDIs had to be submitted as 1400dpi max along the bottom or 1040dpi max up the side. Recently this has changed to 1600 x 1200 as I believe the association (NIPA) got a new projector.
  9. EightBitTony

    EightBitTony Well-Known Member

    I think you mean 1400 pixels or 1040 pixels, not dpi.
  10. El_Sid

    El_Sid Well-Known Member

    When I first started in PDI comps the projection requirements were 1024x768 (SVGA?) which IIRC was pretty much the limit of affordable projectors at the time. Subsequently it rose to 1400x1050 as required by the PAGB for any images submitted for PAGB competions. As most clubs are PAGB affiliates, ususally through their localm federation, they tend to go with these requirements. The PAGB requirements increased again last year to 1600X1200 effective from February this year and, according to this document, there is also 2MB filesize limit which should be easily maintained at the given image dimensions.

    Doubtless there are projectors out there which can handle larger files but only at a high price. I think the PAGB requirements are generally aimed at keeping the image size to a resolution that is within the reach of most clubs. I have a recollection that some dispensation may be available this season for clubs who have yet to obtain a suitable projector though this may be more down to local federations rather than the PAGB itself.
    EightBitTony likes this.
  11. beatnik69

    beatnik69 Well-Known Member

    Thanks for correcting that Tony. :)
  12. Roger Hicks

    Roger Hicks Well-Known Member

    All of which is of course an illustration of why proper prints are a better way do show people your pictures...


    spinno likes this.
  13. dan marchant

    dan marchant Well-Known Member

    As someone who has had to download giant TIFF files for our camera club competition submissions I can tell you that the reason is speed, ease of use and the fact that full size files are simply unnecessary as the equipment can't protect them.
  14. RogerMac

    RogerMac Well-Known Member

    I don't think anyone has mentioned this so I will:
    My photo editor (FastStone) overs a choice of about half a dozen resizing algorithms each with different results. If I do the resizing myself I can see the same result that the audience will see - rather than relying on a randomly chosen result selected by the projector.
  15. dangie

    dangie Senior Knobhead

    Hello Roger
    I often use Faststone Image Resizer. Excellent bit of software.
    I just leave the resizing filter on its default setting. I've never tried any of the others.
    Do you know what difference the others give?
  16. ChrisNewman

    ChrisNewman Well-Known Member

    Absolutely right, of course. And yet I prefer to visit my local camera club (where I’m not a competitor) when there is a projected image competition than when there is a print competition. With a projected image, I and all the other members get a good view of each image. Print images are put on boards, then during the competition, moved one-at-a-time into a well-lit compartment where the judge gets the good view he or she needs, but the print is too small and far away for the rest of us to appreciate it properly. I can join the scrum around the boards during the tea break, but there the images lack the spot-lit effect, and I’ve been surprised just how much better that extra light makes them look.

    Roger Hicks likes this.
  17. RogerMac

    RogerMac Well-Known Member

    I use Lanczos 2 as my default that claims to be sharper , if I do not like the result I experiment often. , ending up with bicubic.

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