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OMD Technical Question.

Discussion in 'Olympus Cameras' started by ice_man, Jan 17, 2013.

  1. ice_man

    ice_man Mu-43 Regular

    Dec 19, 2012
    Hi guys, I have a few technical questions which I am very confused.

    I always have been using 240dpi when saving my raw files in ACR with my FF camera. I just noticed that there's a dpi setting in the OMD as well and the default number is at 350dpi.

    What number do yo use here? Would it degrade the quality of the jpeg/raw output if I set it to 240dpi?

    Second question is, I am used to FF or APS-C aspect ratio (Image Aspect) of 3:2 or roughly 5616x3744 in FF. The default setting in the OMD is 4:3 or roughly 4608x3456. If I choose the 3:2 ratio I get 4608x3072.

    My question is, does it degrade quality if I choose 3:2 over 4:3? Or is it just the cropping?

  2. FrayAdjacent

    FrayAdjacent Mu-43 Veteran

    Dec 5, 2012
    Austin, TX
    I would suspect that changing the aspect ratio would make the output area SMALLER, because you can't go beyond the size of the sensor as it is. You'd have to cut area out to get to the new aspect ratio. That shouldn't change the quality of the image, only the size.
  3. mattia

    mattia Mu-43 Hall of Famer

    May 3, 2012
    The Netherlands
    - DPI is a fairly irrelevant, outdated measure. Simply a flag in the EXIF that tells certain devices how big a print should be. Doesn't affect the image itself at all, resolution (pixels) is all that really matters.

    - The RAW file will always capture the full 4:3 image. The other aspect ratios are crop settings and apply to JPG files, so you simply cut off part of the picture, nothing else.
  4. b_rubenstein

    b_rubenstein Mu-43 All-Pro

    Mar 20, 2012
    Melbourne, FL
    It has no effect on JPG either. It functions as a scaling factor. If your editing software defaults to 350 dpi, then a file would show as being be 4608/350 inches wide. Set it 240 and would show 4608/240 inches wide.
  5. Mikefellh

    Mikefellh Mu-43 Top Veteran

    Jun 7, 2012
    Toronto, Canada
    Not exactly, it's just as relevant today as ever. It tells the software how many pixels from the image to print within one inch of paper. If you have a 300x300 pixel image and you set the dpi to 300 you'll get a one inch square. If you set te dpi to 150 you'll get a two inch square. 600dpi a 1/2 inch square.

    The thing about DPI is you can set it any time before printing, and you can change it as many times as you want since it's just a stored number.

    If you always print at the same DPI it makes sense to set the default in the camera...but if you crop, and or print to a different size paper it would make more sense to set the print dimensions and et the software figure out the di for itself!
  6. dwig

    dwig Mu-43 Top Veteran

    Jun 26, 2010
    Key West FL

    The PPI setting in an image file is a very useful feature.
  7. slothead

    slothead Mu-43 All-Pro

    Aug 14, 2012
    Frederick, MD
    I didn't see an answer to the question "What number do yo use here?" I didn't realize that it was adjustable. I am used to 300 dpi, so I would change it to that. Now I need to go find out how to adjust it!
  8. mattia

    mattia Mu-43 Hall of Famer

    May 3, 2012
    The Netherlands
    My point is that unless you print yourself, it's pretty pointless. I don't print to a specific DPI level, I print to a certain size. I check DPI to get an impression of whether my resolution is good enough, no more, no less, and what DPI I accept depends on viewing distance.
  9. Mercurio

    Mercurio Mu-43 Veteran

    Jul 17, 2012
    Bogotá, Colombia
    I will try to explain briefly the use or "DPI", please excuse my English.

    Prints and printers use different numbers of "dots per inch", depending on the quality of paper and the quality of printed material. A very high quality image book could be printed with a very high "DPI" number, a current magazine with coated paper perhaps will use 300 DPI, a newspaper something around 72 DPI. It has to do with how much ink will be put on the paper, depending of the "grid" of the printer device. If you print with 300 DPI on newspaper paper, you will get a mess, if you use 72 DPI on a very fine and coated paper, the image quality will be coarse.

    On the other hand, you have an image size and type that can be "adjusted" to the amount of DPI needed for printing purposes. Normally an off-set will print with at least four different inks: CYMK or cyan, yellow, magenta and black, an ink-jet printer will use just three channels: RGB, red, green and blue.

    You can downscale your image to fit exactly to the size needed, but you can´t upscale it. If you do, your software will be interpolating - in other words, inventing - dots to get the amount needed. This means that, if you want a real high quality image printed on a very fine paper, you will need to start with an image that has at least all the needed information for the final size. This is one of the reasons because FF cameras are needed to produce such large images: they will allow to print large high quality images on high quality papers. If you don´t intend to use your images for this purpose, the size can be a lot smaller.
  10. RobWatson

    RobWatson Mu-43 Hall of Famer

    Note that if you submit images to scientific publications they insist on 300dpi as a minimum. Generally the paper quality in the printed form cannot support more than ~100dpi so it is largely atavistic holdover from who knows where.

    Upsizing an image to get the print size desired so as to conform to the 300 dpi minimum is fine so long as the perceived quality of the printed image is still OK.

    Try explaining this to researchers is almost pointless so I just resize the image and say "here you go" ... kind of expect more from them but really not worth the effort.
  11. rkelac

    rkelac Mu-43 Regular

    Feb 15, 2011
    Your English is fine but sorry, there is not much I agree with. First, we should be using PPI not DPI when talking about printers. Modern printers use many dots (and even different sizes of dots) to reproduce what can be thought of as a pixel. Printers can print on very rough paper at high resolution and can look fine. I sometime use uncoated watercolor paper and the prints look great. Inkjet printers use CMYK inks (but some add additional inks to increase the color range). With modern programs, downscaling and upscaling images both work fairly well. Most Canon printers only use 300 or 600 PPI and Epson 360 or 720 PPI. Either your program or the printer will upscale or downscale to these values before further processing to get DPI.
  12. flash

    flash Mu-43 Hall of Famer

    Apr 29, 2010
    1 hour from Sydney Australia.
    The primary function of setting a DPI setting in camera is for direct printing. Different type and brands of printers have a different native base resolution for printing. You may experience modest improvements in print quality if you give a printer the input that best matches it's print output.

    At the risk of opening a rather large can of worms the complete answer needs some clarifying. There are already a few incomplete statements here (inkjet printers don't print using red, blue and green inks, for example) that might be better understood with some more detail.

    Firstly I'll explain my use of terminology. DPI or dots per inch refers to how many actual dots of ink are placed on paper per inch. PPI or pixels per inch refers to how many pixels a non-ink/pigment device uses per inch. For example when someone says their monitor has a resolution of 72dpi (or 120dpi+ on modern devices and up to 330ppi on current Apple screens) they should have said 72ppi. Digital files should also refer to ppi. But if you see dpi and understand that some people use the terms interchangeably, you'll survive.

    Output settings and quality depend on a few things. Firstly there's the file size. Assuming that you shoot at the native resolution of your camera this is fixed. Changing the output ppi has no effect on this number. If your camera has 4000x6000 pixels, (that's about a 24MP camera) then that's what it has. Iff you upload a 900x600 pixel image to the web then that's what the file contains. It doesn't matter if it's tagged at 72ppi or 720ppi. That only matters to the printer.

    Then we have the output device. An easy comparison is an original ipad versus a newer "retina" display iPad which has exactly double the resolution horizontally. If there is no interpolation of the original file the higher resolution display will show a physically smaller image. (the same number of pixels in less inches). Simply put the higher the ppi display on your monitor the smaller stuff looks. Because the eye has resolution the smaller image will appear sharper until the display outresolves the human eye. After that it just looks smaller but not sharper. Apple are being very conservative with their "retina" definition. Most adults don't resolve anywhere near 314dpi. Most over 30's are closer to 200dpi even if they don't wear glasses. Simply put when it comes to display on a screen ppi is irelevant. The file is either the right size or it isn't. You can't possible format an image for everybody's monitor because you don't know what the ppi of their display is. But you're better making the files bigger than you have to. Things generally look better interpolated down compared to interpolated up.

    The resolution to printers is more complex. To have the highest possible quality print you need to meet or exceed the resolution of the viewer (measured in dpi) and then send a file to the printer that optomises its capabilities (measured in ppi). For a minute let's assume that everyone reading this can resolve 240dpi at 1 foot distance. If you have a file thats 2400 pixels across and you want the highest visual quality then you can make a 10" print. But at 36" (about 1 meter) we can only resolve about 160dpi. So we could make a print that's 15 inches across. In both these case sending a file to the printer at a higher resolution will make n visual difference. Both prints are resolving more than we can see at those distances.

    But.... There's always a but.

    Printers don't print all colours. They work with just a few colours and mix them to create the huge range we can print. That mix of the basic colours is called a dithering pattern.And every printer brand has it's own way of doing it. To get the ultimate quality print the printer expects a file resolution that fits nicely into the dithering pattern it produces. This is based on the way the printer lays down the inks and how they mix.

    All offset printers use cyan, magenta and yellow inks. If you mix those to gether you get black. But since we can't make pure cyan, magenta or yellow we end up with a dark brown. So theres a fourth ink, black which is called the key. Hence CMYK. Offset printers lay down lines of toner. In two passes the toners are mixed to create the colours of the rainbow. Offset printers lay down 150 lines per pass. Two passes gives us the 300dpi we have all heard about. This is why graphic designers often insist on a 300ppi file. Too bad a lot of them don't know why they need a 300ppi file. I get tired of being asked for files that are 300"dpi" for web use. for web use ppi and dpi are meaningless. It's the total number of pixels that's important.

    Inkjet printers mix inks by squirting them on to paper at high pressure. Each drop comes from a nozzle. It's the number of squirts that are mixed into a single point that determines the printers native resolution. For Epson it's 360dpi and for Canon it's 300dpi. ALL inkjet printers are based on CMYK inks although other have been added to increase the colour gamut of inkjet printers. The difference between this and an offset printer is that an inkjet printer still expects a RGB (red, green, blue) based file where as the offset printer needs a CMYK file. Inkjet printers do the conversion from RGB to CMYK on the fly. An offset printer needs the designer to do an RGB to CMYK conversion (an art in itself) before sending the file to print.

    Other printers need their own input resolutions. a Llambda printer want 400ppi files. I had an Olympus dye thermal printer that insisted on a 312ppi file. If you sent it anything else the results were foul.

    So does this mean that you can make bigger prints on a Canon printer than an Epson one, or a Llambda?

    No it doesn't. The image quality still depends on the eyesight of the viewer and the viewing distance. The subject matter also counts. The more detail in the image the quicker it's easy to see the file fall apart. You can enlarge a big piece of blue sky almost indefinitely. A forest, not so much.

    So what file do we send to the printer? Well, it's actually pretty easy. You determine the maximum print size based on the file and viewing and then interpolate it (add or remove pixels) to match the native resolution of the printer. (WHICH IS WHAT THE SETTING IN THE E-M5 MENUS IS FOR). Let's go to the earlier example. You want to make the biggest print from a 2400 pixel file and you'll be expecting it to be viewed at 1 meter. So you can make a 15 inch print. For a 15 inch print on your new Canon printer you need to send it a 4500 pixel file (15"x 300ppi) for the best pixel to ink conversion. So you just interpolate the 2400 pixel file to suit that. (ie: you'll interpolate from 2400ppi to 4500ppi. If you use Lightroom or modern versions of Photoshop then this is all done for you. All you do is plug in the native resolution of your printer in the print module and the software does the rest. If you're sending files out to be printed you should provide the interpolated files. That way you can do some appropriate sharpening and noise reduction for the individual file you send. As modern printers improve the differences between sending an ideal file and a slightly less so one are shrinking. On a modern Epson it's not the end of the world if you send it a 300ppi file or if you send a 360ppi file to the lab.

    Oops. That's a bit longer than I planned. Sorry.

    • Like Like x 3
  13. Mercurio

    Mercurio Mu-43 Veteran

    Jul 17, 2012
    Bogotá, Colombia
    Instead of arguing about your affirmations, may I suggest a little reading that can be helpful:

    Adobe Photoshop * Image size and resolution

    For instance:

    "About printer resolution
    Printer resolution is measured in ink dots per inch, also known as dpi. Generally, the more dots per inch, the finer the printed output you’ll get. Most inkjet printers have a resolution of approximately 720 to 2880 dpi. (Technically, inkjet printers produce a microscopic spray of ink, not actual dots like imagesetters or laser printers.)

    Printer resolution is different from, but related to image resolution. To print a high quality photo on an inkjet printer, an image resolution of at least 220 ppi should provide good results." (...)

    Resampling is changing the amount of image data as you change either the pixel dimensions or the resolution of an image. When you downsample (decrease the number of pixels), information is deleted from the image. When you resample up (increase the number of pixels, or upsample), new pixels are added. You specify an interpolation method to determine how pixels are added or deleted."
  14. flash

    flash Mu-43 Hall of Famer

    Apr 29, 2010
    1 hour from Sydney Australia.
    I agree with ppi being the incorrect term for printers. But the rest is OK in a broadly general way, as was much of what you wrote. I don't thin k there was anything personal in there.

  15. mattia

    mattia Mu-43 Hall of Famer

    May 3, 2012
    The Netherlands
    Bottom line is that your best bet is to keep as many pixels as humanly possible, and only start worrying about what the 'DPI' is set to when printing enters the picture. And all reputable print labs I use don't care about the DPI setting, just resolution, and adjust/interpolate/etc to optimize the outcome based on that. Not based on the DPI flag in the EXIF file, which does nothing at all to change the information recorded in the image.
  16. rkelac

    rkelac Mu-43 Regular

    Feb 15, 2011
    Yes. I agree what you put in this post. Maybe I was too brief to make this clear. We are usually concerned about PPI of the image when sending an image to a printer -- not so much the actual dpi of the printer. The printer converts the image to its dpi.
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