Need help in calculating digital camera's MP

Discussion in 'UK Photography' started by aniramca, Jan 2, 2009.

  1. aniramca

    aniramca Guest

    For a 46 in high definition TV (1920x1080 Panel resolution) - 1080p
    Full HD definition, the screen size of the TV is 40 in. x 23 in. ( 102
    cm x 58 cm). How many MP digital camera that I need to have JPG
    photos, so that I can watch clear, sharp, crisp JPG photos on the TV?
    I must admit that I don't have much knowledge about the pixels in
    digital cameras,etc. and how that translates into the high definition
    TV. Therefore, I do need practical, layman terms answers for info or
    links to specific discussion to any websites.
    What about for the 52 in. TV, 56 in. TV, etc?. Is there a chart
    available somewhere?. I recall a table showing how MP is connected to
    photo print sizes (at the photo printing stores). But this screen size
    is much larger than those listed - perhaps more for poster sizes.
    Someone may ask on how close you are watching the TV screen... and I
    am thinking about relatively close range, say 5 ft distance.
    Thanks for the info!
    aniramca, Jan 2, 2009
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  2. aniramca

    Don Stauffer Guest

    Roughly two megapixels. There may be an aspect ratio problem, but
    resolution is not a precise number anyway. Multiply the screen panel
    resolution to get the appropriate resolution of the screen. Your image
    should equal or exceed that value for good results. It doesn't really
    depend on screen size, merely the number of pixels, which is determined
    by whether the set is HD or SD, and if HD is it 720 or 1080. Interlaced
    vs progressive is immaterial to showing stills.

    Sure, if you view it from a large distance away, you COULD get by with
    less resolution, but the requirement for viewing on a TV is not
    strenuous, so why not shoot with enough resolution so that the image is
    not the limiting factor?
    Don Stauffer, Jan 2, 2009
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  3. aniramca

    ray Guest

    Basically, 1920x1080 is about 2mp - anything beyond that is overkill -
    you can't display more than the resolution of the output device.
    ray, Jan 2, 2009
  4. It's acalculia.

    And I think the proper word would be dyscalculia, anyway.

    Scarecrow: I haven't got a brain... only straw.
    Dorothy: How can you talk if you haven't got a brain?
    Scarecrow: I don't know... But some people without brains do an awful lot
    of talking... don't they?
    Dorothy: Yes, I guess you're right.

    -- Wizard Of Oz
    Gaston Ryan Coake, Jan 2, 2009
  5. aniramca

    Rob Morley Guest

    It is indeed, like the related conditions of dyslexia and dyspraxia.
    Rob Morley, Jan 2, 2009
  6. aniramca

    Paul Furman Guest

    Common aspect ratios:
    16:9 = 1.77 HD video
    8:6 = 1.6 Widescreen LCD
    3:2 = 1.5 DSLR
    4:3 = 1.33 Compact digital
    10:8 = 1.25 8x10" print

    Computer wide screen monitors are taller than they need to be:
    1200x1920 1:1.6
    1080x1920 1:1.7
    Compact digitals are a 1:1.3 aspect ratio (4:3)
    If you aren't going to crop to fit the screen and it's only 1080 high,
    there will be considerable wasted space on the sides:
    1080x1404 = 1.5MP
    If you do crop and the screen is 1200 pixels high:
    1476x1920 = 2.8MP

    Digital cameras have an anti-aliasing filter which blurs the image some
    to avoid moire patterns on striped detail so you can get a considerably
    sharper image by reducing to around 50% so:
    2952x3840 = 11.3MP

    Maybe that's overkill but not far off. If you are just turning down the
    capture size for your camera, you will get this advantage. Full size
    pixels are definitely less sharp than if you reduce some. A 3MP native
    image will be noticeably softer than a 10MP image reduced to fit.

    Paul Furman

    all google groups messages filtered due to spam
    Paul Furman, Jan 2, 2009
  7. aniramca

    John Sheehy Guest

    wrote in :
    The HD screen is 1920 * 1080 = 2,073,600 pixels, or about 2.07MP. The
    aspect ratio is different than most digital camera formats, though, which
    are 4:3 or 3:2, so if you want to get the entire image on the TV screen,
    you're going to have to leave some black space on screen. 2/3 of 1920 is
    1280, which is larger than 1080, so 3:2 isn't going to be a perfect fit.
    To find the largest 3:2 image to fit, you have to multiply 1080 by 3/2,
    and you get 1620. The largest 3:2 image that will fit on screen, is
    therefore 1620 * 1080, which is 1,749,600 or 1.75MP.

    For 4:3 images, 3/4 of 1920 is 1440, which again is too large, so the
    largest 4:3 image displayable on the HD screen is 4/3 * 1080 = 1440
    pixels wide, and the largest image is 1440 * 1080 = 1,555,200 or 1.56MP.

    These figures, of course, assume that you are supplying the exact pixels
    you want displayed to the TV. Most (if not all) TVs will resize the
    JPEGs to fit the screen. You have two choices; give the TV the entire
    higher-MP image, or give it at the TV resolution yourself, in which case
    you will have control over how sharp the pixels are rendered.

    I would say that you will generally have the best results with the
    highest MP originals that you can get, unless the method, used by either
    you or the TV, to downsize the image, is the Nearest Neighbor algorithm,
    which makes images look extremely sharp-looking but falsely detailed and
    much noisier than necessary. Any image 1.75 or 1.56MP or greater will
    take advantage of the resolution of the screen to some degree, but at 2x
    the MP you get a good deal of the maximum resolution possible on the
    screen, and at about 4x, about most of it, but newer cameras with many
    MP, despite illusions of greater noise, actually have less noise than
    older 3 to 8 MP cameras when all images are downsampled with Lanczos to
    the same size for the screen. So, for sharpness, etc, 2x to 4x the
    figures of 1.75MP and 1.56MP are generally sufficient, but for minimal
    noise, going to higher MP cameras can be beneficial, too, if that
    concerns you.

    Using the Lanczos method to downsample images in the freeware PC program
    "Irfanview" (http:/// is a very good and free way to
    get excellent downsampled images. Its batch-conversion feature will
    allow you to apply sharpening to each one automatically, should you want
    Physical size is irrelevant to the calculations you are using; only the
    number of pixels on the screen matter.
    That's just someone's recommendations, concerning where you will see lack
    of resolution in prints. This does not affect the low-res TV screen.

    Despite the term "High Definition" for TV, it is only "high" relative to
    the extremely low historical TV resolution, which is only about 0.35MP,
    and even worse than that because old analog TV broadcasts didn't even
    have that kind of information in them. Color was blurred across
    horizontal lines, and could only exist in certain sequences. HD is
    actually very low resolution as far as still images are concerned, and
    almost any camera from the last few years hgas more resolution than a HD
    TV screen can show.
    John Sheehy, Jan 3, 2009
  8. aniramca

    John Sheehy Guest

    A 3MP camera will only give better results than a 12 MP at 3MP or lesser
    display if the lens on the 12MP is much worse, in an absolute, analog
    sense. Pixel-level "lens" quality is totally irrelevant to this concern.

    A 12MP image downsampled to 3MP will have less noise, and more pixel-level
    color and luminance resolution than a native 3MP camera, with the same
    quality lens.
    John Sheehy, Jan 3, 2009
  9. Does Irfanview use a high enough order of the Lanczos algorithm to do
    the best job? I've seen some doubts expressed about that, but I know
    Irfan keeps updating, and I'm not up on the technicalities. In
    practice I do find Irfanview's Lanczos downsizer does a good job on my
    images, clearly better than some other downsizers, some of which are
    surprisingly crude. I'm just wondering if there's anything even better
    Chris Malcolm, Jan 4, 2009
  10. aniramca

    John Sheehy Guest

    Back when cameras had 3 MP, quantum efficiencies were lower. Now, they're
    leveling off, but read noise is not increasing as fast as linear pixel
    density (sensor PPI). In fact, it is generally decreasing, so image-level
    read noise is generally going down.
    John Sheehy, Jan 5, 2009
  11. aniramca

    John Sheehy Guest

    I don't know how it compares with other Lanczoses; all I know is that it
    looks pretty good to me, and I see no need to switch. I wish I had Lanczos
    available in PS for the on-screen zooming.
    John Sheehy, Jan 5, 2009
  12. aniramca

    John Sheehy Guest

    NR is madness, at the level it is practiced in many cameras, especially P&S
    cameras. Companies do NR for the idiots who judge cameras at 100% pixel
    view, and wouldn't know an honest-looking image if it bit them in the face.
    I only concern myself with RAW noise.
    John Sheehy, Jan 6, 2009
  13. aniramca

    TheRealSteve Guest

    Especially since you can almost always to NR better on your PC than in
    the camera.

    However, I disagree that 100% pixel view is unimportant. It all
    depends on how big you want to print your pictures. I sometimes make
    prints out of my 10MP DSLR at up to 20x30". Even if I don't have
    wasted pixels due to cropping (which I frequently do even if just to
    get to the correct aspect ratio) that works out to under 130
    pixels/inch. And they're often viewed at only like a foot away. In
    this case, pixel level noise, chromatic aberration, etc., are all very
    important. There's no way I'd even bother to make a 20x30" print from
    a 10MP P&S because it'll look like crap. But from a 10MP DSLR they
    can look great.

    TheRealSteve, Jan 6, 2009
  14. Yes I reckon with a decent lens you can still get good detail at 60" x 40".
    I wish I could afford prints that size but I know the detail is good because
    I have done small test prints of a portion of this sized photo.

    Roger Blackwell, Jan 6, 2009
  15. aniramca

    Bruce Guest

    That depends.

    If you ask Sony, they will tell you that it takes 6.2 megapixels to make
    a 1920x1080 picture. And indeed it does, because it takes three single
    colour pixels (red, green, blue) at the position of every displayed
    multi-colour pixel.

    Sony the TV manufacturer is scrupulously honest about this.

    On the other hand, digital camera manufacturers - including Sony the
    digital camera manufacturer (no relation?) - will tell you that a
    digital camera with a 6 million pixel CCD or CMOS sensor will give you a
    6 million pixel image. Yet each of those 6 million pixels is either
    red, green or blue, set in an arrangement known as the Bayer pattern.
    There are 1.5 million red, 1.5 million blue and 3 million green pixels
    on a 6 million pixel digital camera sensor.

    In summary, according to Sony the LCD TV manufacturer, you need around 6
    million single colour pixels to make a 1920x1080 image on a TV. But
    according to Sony the digital camera manufacturer, you apparently need
    only about 2 million single colour pixels to make a 1920x1080 image with
    a digital camera.

    Someone is being economical with the truth, and it is not the
    manufacturers of LCD TVs.
    Bruce, Jan 6, 2009
  16. aniramca

    TheRealSteve Guest

    Why not? If you use something like a 35mm 21MP 1DsMkIII and print to
    60x40", you're getting over 90 ppi. While not great, if viewed from
    more than a foot or two away, you'd wouldn't be able to make out
    pixelation if the printer is doing any interpolation. But once again,
    pixel level noise, CA, etc, would be very important.

    TheRealSteve, Jan 7, 2009
  17. aniramca

    Ray Fischer Guest

    No it doesn't. 1920x1080=2,073,600 which is 2MP.

    And why would I care what some marketing weasel tries to claim?
    Wrong. A pixel can be any color. Limiting it to R, G, or B is
    Obviously not.
    Ray Fischer, Jan 7, 2009
  18. Sorry I didn't spell it out fully, I was assuming the use of interpolating
    software. I have a Canon 50mm f1.4 lens and have tested the detail at 60" x
    40" and find it quite acceptable.

    Roger Blackwell, Jan 8, 2009
  19. aniramca

    Scott W Guest

    21MP on a FF 35mm camera is not all that high, any decent lens should
    be able to make full use of the pixels. The pixel density of a 21MP
    FF camera is very close to the pixel density of a 8MP 1.6X crop
    camera, and there are many lenses that make full use of the 8MP
    camera. My 50mm f/1.8 has more then enough resolution for that pixel

    Now whether 21MP is enough pixels for a 40x60 inch print is another
    matter. If viewed from far enough back it would look good, maybe even
    great. But get at all close and it is going to look pretty soft IMO.
    21MP on a 40x60 inch print would be the same pixel density as a 8 x 12
    inch print with 0.84 MP

    Scott W, Jan 8, 2009
  20. aniramca

    Scott W Guest

    So use a better lens, not everyone uses zooms exclusively.

    I know that I get more scene detail when I put a 1.4x tele-converter
    in front of my 300mm f/4 lens, compared to just using the 300mm lens.
    If the lens was not resolving more then the sensor could pickup then
    there would be no added detail, there would be more pixels / degree
    but all detail that could be seen with the 1.4 converter would also be
    visible without the converter.

    If you look back into the camera what the converter is doing is making
    the pixel density higher, from around 6.5 microns pitch to around 4.6.

    With both my 50mm and 300mm lens I often get aliasing, something that
    I would not see if the sensor had more pixels then needed, in fact it
    tell me for those lenses I could use more pixels/mm.

    Scott W, Jan 10, 2009
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