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Old Nov 1, 2002, 11:21 AM   #1
smf
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Default Resolution and Printing

Hello,

I need a few questions answered concerning printing and resolution.

I've heard that one needs about 300 dpi on a print to make it "look good". My current camera is 3MP, or about 2000x1500 pixels.

This would make me think that I can print a 5x6" photo (2000/300=6, 1500/300=5), and beyond that I would be stretching things. However, I am quite happy with the 8x10's that I print.

I want to print some 13"x19" photos and am wondering how much "resolution" one would typically require in a camera to do this, producing photos which look like photos and not computer generated images. I am looking at the Nikon D100 and the Canon D60 and wonder if they would be up to the task? I must be in error in the above thinking as they are 3000x2000 pixel cameras, but it seems that for $2000 one should be able to print high quality photos larger than 10"x6".

Next question is in terms of file sizes generated by different cameras - for example with the Nikon one can generate a 11MB NEF file, a 4MB jpeg, etc. But they are all 3000x2000 pixels - yet in the reviews people talk about what great prints one can get from the larger files. Can someone explain this, given that the pixels are the same?

Last question is in terms of the printer - it says it prints 2400 dpi. I assume that when I enlarge a 2000x1500 pixel image up to 13"x19" the printer is just doing a 2400 dpi print of the visible pixels contributed by the camera and not sharpening the image in any way. Does this sound correct?

And if I need 300dpi for the photo why wouldn't a 300 dpi printer look "pretty good"? Does a 2400 dpi printer produce an image that one can really call better?

thanks,

Steve
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Old Nov 1, 2002, 11:30 AM   #2
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300 real pixels per inch is a bit unrealistic. If that was the case you wouldn't even be able to get an 8x10 from a 6mp DLSR and that is absolutely not the case. IMO 150 pixels per inch is about the lowest you want to go to avoid obvious jaggies. At that a 2mp camera makes for adequate 8x10s and a 5-6mp gets you to 13x16. You may want to "upres," use software interpolation to make the bitmap bigger as this often improves the apparent image quality. I find that the smart resize in Paintshop pro does an excellent job, slightly better than bicubic resample in the same program.
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Old Nov 1, 2002, 2:13 PM   #3
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You could have a look round here:
http://www.stevesforums.com/phpBB2/v...ghlight=poster

However, there will be many issues to large prints. But if you were being critical, you might say, if I shot the same scene with a film cam and put both enlarged prints together, would I see a difference? The chances are you would, but on it's own, without a reference to compare, the digicam print could be very good. The problem with going bigger is we still put the prints at the same distance in front of our eyes!
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Old Nov 1, 2002, 3:08 PM   #4
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With my 3mp Olympus C3000, I have printed good 8X10 photos. With my 4mp C4040, I have printed good 11X14 photos. I would recommend a 5mp or 6mp camera to produce 13X19 prints.
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Old Nov 1, 2002, 8:58 PM   #5
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:P The diffrence in file size is due to compression. jpeg reduces file size greatly but a small amount of the image quality is lost. Larger file types which tend to be either low compression or no compresion keeps 100% of the picture data but require a larger file. To see this clearly take three pictures. Most camera's have about three diffrent jpeg compression settings like normal, fine and super fine or whatever they call it on your camera. Look for info on jpeg in your camera manual. Take a photo of the same object at the same distance in each of these diffrent compressions. Bring them into whatever photo editor you use and zoom way in on a spot (maybee 5005-1000% in photo shop). The diffrence between pictures should become very clear. Even in the highest jpeg setting you still get the same type of picture loss that you are seeing between the diffrent jpeg settings, just not as much. You have to go to raw or whatever uncompressed file type your camera uses. Try taking the same picture in whatever your camera's largest file size is and zoom in and compare it to your largest file size jpeg. You will see that this picture loss due to compression is gone. Memory cards are getting cheaper fast!! It wasn't very long ago they cost a lot more (and if you don't shop around they can still be kind of expensive) so there was and to a much lesser extent still is reason to use a compressed file. It just allows you store more pictures if you do not have the largest card in the world.
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Old Nov 2, 2002, 8:28 AM   #6
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Storage in the cam isn't everything. The feel and responsiveness of a cam depends a lot on how fast the cam is processing large image file data and internal memory buffer size.

So we don't just need larger media, but faster media, faster processing, auto focus, white balance and flash recycling etc etc ! Oh - and I forgot the USB interface for downloading all these big pic. files.
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Old Nov 4, 2002, 1:27 AM   #7
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Let's see if we can put some of this into perspective. First, the 300 dpi figure comes from what is generally needed from scans of film or transparency to satisfy the conditions of some commercial printers. This is not a hard and fast rule. Some printers do very well at considerably less and some require 400 dpi.

Even the highest resolution removable lens dSLR type cameras only produce a native image of around 10x15 at 300dpi. Yet, these same cameras are capable of turning out beautiful crisp gigantic prints far beyond what can be done with 35mm film. How then does this work?

It all happens because of something called "interpolation." This is one of a number of mathematical formulae which actually create data which would have been captured had the sensor of the camera had more photodiodes (higher resolution) at intermediate positions between those actually capturing data. By examining the values of adjacent existing real data points (pixels) the software or firmware actually makes a very educated "guess" at what those intermediate data points would have been had there been additional data points on the sensor. It then creates these values and does this throughout the image.

How well then does this work? Very well indeed, especially if there were sufficient pixels alloted to a given geographical area of capture to properly define the boundaries of fine detail.

Let's take an example from real life and perhaps we can begin to see how this works. The human brain actually does a good bit of its own interpolation. Find a newspaper image of several people taken at a distance. Examine the faces an decide if they all have eyes, noses, eyebrows, etc. Of course they do! Now find a rather large portrait of a single person and do likewise. Same result? Of course. Now take a strong magnifying glass and examine the large "portrait." Look carefully at only one of the subject's eyes. Does it still look like an eye? Yes it does - but you can probably see the "dots" which make up the eye - but even at strong magnification it still looks like an eye. Now do the same with the distant photo of several people. Wait!! What happened to the eyes?? What the brain was quite happy to accept as eyes, nose, eyebrows, etc., when viewed without magnification now appear to be only a few dots or "marker pixels" which look absolutely nothing like we imagined them to before looking at the features under strong magnification.

So we have learned that things are not always as they appear. In the large portrait type image, sufficient pixels were used to paint the eyes and fine details so that we could, in isolation, still identify the features. In the distant shot of several people, insufficient pixels were alloted and only our "expectations" made us think that we were seeing true detail.

In the case where we have sufficient pixels alloted to properly define these detail boundaries, an interpolation algorithm can easily enlarge these features to nearly any conceivable size with great accuracy. Where insufficient pixels were alloted, the results of attempted interpolation would be very unsatisfactory at best and probably comical if enlarged to any great degree.

So, how does this relate to image capture resolution and possible print sizes? Even a low resolution camera - say 1.5 megapixels, can create an excellent 8x10 if sufficient pixels are allocated to a small enough area of geography to properly define boundaries of fine detail. With a human head-shot, excellent 8x10's can be printed from a low resolution camera. On the other hand, were one to photograph a basketball team or school class of say 30 students and expect to enlarge it to 16x20 or so, even a 35mm film camera would be a poor choice. This would be better done with a medium format film camera or one of the new 16 megapixel high resolution digital backs or perhaps a Canon EOS-1Ds or Kodak DCS-14n.

The bottom line is that you can always keep what you actually have with a good interpolation algorithm, but you can never create what was never truly captured in the first place. The difficulty lies in knowing whether or not you have actually captured sufficient true detail. The easiest way to decide is probably by trial and error. We know with trial and error that gigantic sharp, clean head shots can be printed (at sizes up to even 8x10 feet) from a good quality 3 mega-pixel capture with a camera like the D30. Noted Hollywood photographer Vincent Versache has demonstrated quality 8x10 foot prints made with a 2.66 mega-pixel Nikon D1 at the PMA shows. When viewed from a normal viewing distance, they are super clean. On the other hand, a landscape with lots of distant detail printed at more than 8x10 "inches" from the same camera would likely be unsatisfactory.

Hope this doesn't muddy the waters too much.....

Lin
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Old Nov 4, 2002, 6:42 AM   #8
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Lin.. your contribution, based on how we see pictures is very relevant. Translating this to present digicam performance, I agree that scene detail and visual masking by the brain (your points!) are a factor in how we might perceive printed quality.

Compression is already fooling us, so subjecting every area of detail on a print to magnification will show defects. What most of us want to know is where the 'cliff edge' is for the size of print we want, to satisfy our individual quality expectation for scenes with varying degrees of critical (to compression) content.

However, compression algorithms are either working hard and less transparent for detail or not hard for softer pictures, pixel resolution could be seen the same way.

So, the conclusion is we can't predict whether there will be sufficient pixels or what the detail threshold will be, unless we can characterise the scene against our individual scale of expectation..

We have been fortunate with film in that emulsion quality surpasses for most critical scenes, but I do recall many debates about 35mm and larger film formats - so digicams seem no different!
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Old Nov 4, 2002, 1:11 PM   #9
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Default Resolution and printing

For a newbie with a 2 mp Oly D510 zoom, shooting action sports and landscapes with very few headshots, and using Elements to improve and crop to size (5x7 and 4x6) before uploading to a website for printing, should I set resolution at 240 or 300 for best results in the crop tool settings? I just don't have my own printer and can't experiment to see which is better. Thanks, folks.
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Old Nov 4, 2002, 1:19 PM   #10
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You really need to inquire and ask what the print resolution requirements are. Some printers need 300 dpi, some need 400 dpi (Fuji, etc.). You would be probably be safe with 300 dpi unless they are using inkjet printers and then that may be overkill.

Lin
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