Very large Images

[Richard Ellis]

Our local photography recently had a discussion about very large images - those taken by Hassalblad and similar cameras, with film sizes of 4 X 5 inches or bigger. These result in very large files - eg a 24 X 36 picture at 300 dpi is 77,760,000 pixels! In a nutshell, Digital can't do this, because of the difficulty and cost of producing a sensor that big. The solution is to take a lot of digital images, and stitch them together. For a variety of reasons, this is easier said than done - BUT, there are solutions, some of them not too expensive. One is under development, expected to be available in 6 - 8 weeks. It consists of a mechanism which allows the attachment of a lensless digital SLR to the back of your large camera, and takes a lot of digital images, which can then be stitched together.

The other need, which can be used by any of us, is much improved stitching software, which uses more sophisticated algorithms than that commercially available. In particular, it can handle a square image - ie a combination of 9 images, in rows of three.

It is too big to post here, but if anybody is interested, I can send you the pdf version of the slide show, which provides the summary of the presentation, and some addresses for contacts, including free software.

[Doug Nelson]

While it is sound theoretically, in practice a print can't hold more than about 200dpi of detail, and this is assuming you're looking at it close up. At a normal viewing distance for a 24 X 36 print you'd need under 100dpi, which is about 8MP.

Granted, a 24 x 36 print from an 8MP camera would fall apart if viewed from a foot away, but I've viewed Adam's "Moonrise" from a foot away and it looked really bad

[MBChamberlain]

You could never scan a print that big anyway, you would need to scan it in sections and stitch it together.

The largest viable scan (the point after which scanning at a higher density does not capture additional detail) for a 4x5 negative is 1200dpi or 28.8 megapixel.

Hasselblaud's newest camera has a digital sensor capable of capturing 39mpx (about 200dpi higher). For still life there is even a 128mpx digital camera that uses a triprismed chip. Problem is that it is like a large format film in that it needs TONS of light to get the shot and needs the shutter to stay open for a second or two, and is therefore bad for anything but still life and product photography.

Like Doug said, I can print a 24x36 straight out of a d200 and get comparable print quality to medium format anyway. The larger the print, the less likey it will be viewed close up.

I'd be interested in seeing the product, but If I was going to spend the money for a hasselblaud system, lenses, and this fancy back in addition to a really good dSLR, I'll just take the dive and get the digital back for the hasselblaud. The 22mpx back is going for under $10,000 since the 39mpx back came out.

Michael

[Ed_L]

Originally Posted by MBChamberlain

The largest viable scan (the point after which scanning at a higher density does not capture additional detail) for a 4x5 negative is 1200dpi or 28.8 megapixel.
Michael

Michael,

I find that interesting. Could you explain why 1200 dpi is the resolution where maximum information is obtained? Inquiring minds want to know.

I believe the distance where a print is typically viewed is referred to as the "normal viewing distance", which would be pretty far for a very large print.

Ed

[MBChamberlain]

Ed,

1200 is considered the maximum because that is the approximate resolution of the film. No lens can expose film any clearer than that, so you are just scanning a blurrier image by scanning any higher.

Michael

[Kraellin]

i've seen some decent, not great, but decent stitching software referened on retouchpro. a search shld lead you to the links and sites. however, the biggest problem with stitching isnt the software, it's the photographer. and please, i dont mean all photographers here. some do it quite well.

the first problem is with how the images are taken. the normal, particularly amatuer, method is to overlap the edges of each shot by only a marginal amount, usually just enough to composite the images together later on. this is the wrong way to take the shots. the overlap shld be at least in the 30-50% range to make the job fairly seamless. when done this way you almost dont need any blending/stitching software. and of course, always use a tripod.

and, if you are doing a composite in rows, you'd want to overlap in both the horizontal and the vertical by roughly the same amounts. this might mean you'd have to take more shots, maybe 4 x 4 or even 5 x 5 instead of 3 x 3, but the post process work shld be much easier.

as for the question of resolutions, this seems to be an ongoing battle. when is enough, enough? digital has some a long ways, but i would guess it will never actually truly rival analog. the 'pixel' in analog is based on the size of a photon. digital isnt likely to ever reach those minute levels. but, as mentioned, the viewing range and ability of the human eye to see those kinds of differences is limited. and also as mentioned, 200 dpi is about the maximum resolution for printing. thus, i scan images at 300 dpi and i've never been disapointed in prints with that part of it.

i own one of the earliest models of digital cameras. this poor thing took 640 x 480 shots at i think it was 100 dpi. it was a great toy, a novelty, but hardly worth printing out because of the lack of quality. i've also retouched hundreds of images from 3.1 megapixel cameras. where these are generally suitable for print, i wouldnt own one. i noticed a real lack of resolution, especially when zoomed in to retouch the things. if i were going out today to buy a digital, i wouldnt even start my search at anything below 5 megapixel.

but that still doesnt answer the question, when is enough, enough. i can really answer this question. it also depends a great deal on what hardware you're talking about, whether scanners, cameras, monitors, printers or something else. and there's also the little scam that's pulled where someone claims to have 'high resolution' but they're only doing what amounts to a digital zooming in, rather than an optical zoom. cameras do this and so do scanners. i'm always leary of any scanner claiming 1200 dpi or 2400 dpi, when i 'learned' long ago that 600 dpi or even 300 dpi seemed to do quite nicely on scanners.

now, i know the large format analog camera guys can be extremely fussy about resolutions...and i mean EXTREMELY! you mention 35 mm to some of these guys and they'll make the sign of the cross and get out wooden stakes and garlic to ward you off. as for digital backs to large format cameras, i'd watch the reviews very carefully before buying. i'd also try and find one i could try before i buy and see what you think.

i've also heard of a new type of camera, which is still pretty experimental, if i remember correctly, which uses something like 90,000, or 90,000,000 'lenses' to capture light. in fact, again, i think the link to that site was here on retouchpro somewhere. there was something about that camera which was pretty intriguing....something along the lines of zero lens distortion because of the way it handled photons and that it could calculate exact distances because of the ability to measure exactly where each photon emanated from?...something like that. my memory is sketchy on that one. it may have been something to do with NASA and deep space photography, so dont go looking for this thing in the store

if this digital back is going to do the stitching for you, i'd be real interested in hearing more about it and seeing some actual images when they become available.

craig

[Ed_L]

Originally Posted by MBChamberlain

Ed,

1200 is considered the maximum because that is the approximate resolution of the film. No lens can expose film any clearer than that, so you are just scanning a blurrier image by scanning any higher.

Michael

Thanks Michael. So I'm to assume that would be the same for *any* film?? Does this also apply to different emulsions of both color and B&W?

Ed

[Chance_1]

The world sharpest digital camera is only 1 Megapixel on a 12 x 12 sensor called pancam, and is a panaroma camera.

http://www.space.com/businesstechnol...ed_040114.html

You can buy a perfect panoramic head, and with 6 pans of a landscape exceed the megapixels of a Hassy or any other medium format camera, and save yourself thousands of dollars.

[MBChamberlain]

Ed, that is for E-6 (slide) film, regular film is a little lower, black and white is comprable to the media.

Chance, while it is true that with a good panoramic head and a 1mpx camera you could take a much bigger picture than any camera you could care to mention, I'd rather not tell my model to "hold still for the next two minutes while I move my camera ten times." I'm also not in the mood to buy the $250,000 controller for the head on the rover. Nor for that matter the $100,000 lense. Not to mention that you won't find a 1mpx camera with a decent lens.

Craig, the only time you will scan at 1200 is on a negative. About the best you can do on a print is 300 and still get a clear picture.

Michael

[Chance_1]

Originally Posted by MBChamberlain

Chance, while it is true that with a good panoramic head and a 1mpx camera you could take a much bigger picture than any camera you could care to mention, I'd rather not tell my model to "hold still for the next two minutes while I move my camera ten times." I'm also not in the mood to buy the $250,000 controller for the head on the rover. Nor for that matter the $100,000 lense. Not to mention that you won't find a 1mpx camera with a decent lens.

Michael

You misquote my post !
A panoramic head, costs 75 to 500 dollars, and with it, you can take a d50 nikon which costs about 700 with lens, and I can take pictures of your model, which are of higher quality, higher megapixels and higher sharpness than a hassy. Simple as that !
Obviously, it takes some work in splicing etc. Of course you could avoid all the hassle and buy yourself a 20k Hassy too or a 10k Canon Mark 2 full frame.

My message on the 1 megapixel camera used by Nasa for Mars, was just to inform folks that there is more to megapixels than quantity.

[Ed_L]

Originally Posted by MBChamberlain

Ed,
No lens can expose film any clearer than that
Michael

I guess I read the post too quickly, and that part didn't register. Now I realize it's a limitation of the lens. Thanks for the post.

Ed

[bart_hickman]

Maybe this isn't applicable here, but have you seen autostitch? I've used it for stitching irregular arrays of photos into a seamless composite. I don't think 100Mpixels is any problem for that software--I think I've even done them that large (I can check next time I'm at my computer.) With sufficient overlap, it aligns the images and adjusts perspective and lens distortion to give a pretty good result.

Bart

[ifixpix]

http://clarkvision.com/imagedetail/s...ml#digicamres1

Lots of test images comparing digital capture to scans from different film formats, etc.

[Ed_L]

Interesting site! Thanks for the link. That's one everyone should consider.

Ed