It works the exact same way as it would on a 100 gigapixel panorama.
no, it does not.
let me guess, you're way upside-down in a mortgage with an interest-only subprime loan, too, right?
you guys disappoint me so...and to think, so much experience, wasted.
Your original was a 600x600 pixel image formed from what, an 8x11" page, right? So what's the linear DPI of that?
And you want to compare this to a 100GP panorama?
How in Gods' green earth do you think the two are equivalent, or that this process "works the same way"?
On one hand you're starting with a source image that might be 6dpi if you're lucky. Do you really expect to get good results by downsampling it to 25%, upsampling back to the original resolution and viewing it at 1ft at 100dpi?
"And it doesn't "create extra pixels out of nothing".
Taking a closer look at it: of course it does - where should the additional information come from?
"An interpolation procedure uses a mathematical transformation on the existing pixel data."
yes - what does that mean? You scale the existing information. In a pixel-based image that means you scale up the pixels . . by adding synthesized ones which didn´t exist before. Scaling existent information means to blurr it. That means you blurr the image.
Can you make 10L of beer from 5L? No. You´d have to add some liquid to add volume. No way you have the same beer afterwards.
Ahhh...we're talking math. Let's compare this to taking a Fourier transform of an audio wave.
Imagine we have a checkerboard image--every pixel is black or white, surrounded on four sides by the opposite color.
Now we shrink this to 25%. In other words, we shrink 50% in the x direction, and 50% in the y direction. A simple averaging gives a uniform gray, a more complex algorithm probably also gives gray also. So now when we upscale this uniform grey field by 400% (thats 2*X and 2*Y) we get what?
Now lets start with the original checkerboard, and upscale by 400%. A simple linear interpolation will yeild pixels with various shades of grey, and no sharp lines. What should the correct interpolation do?
Now let's take the original checkerboard and put a silhouette as a layer above it. Invert all of the pixels under the silhouette. Remove the silhouette layer. You can see the image. Now upscale by 1.5 times in each direction. What happens?
Klause is right. The only thing you can create out of nothing is a blur.
get out your scanner and scan an image at the resolution of your monitor (in DPI), crop it to the resolution of your monitor in MP, and follow the steps that I mentioned above.
this idea works best if you make the image square, limiting it by the short side of your display.
keep thinking about it and you'll see what it doesn't matter if you use 200MP upsampled to 800MP for a 20m display printed at 50dpi or just 800MP @ 50dpi or even 200MP printed at 25dpi.
but really the only clue you should really need are the words "50dpi".
If you really and truly understand the significance of that phrase, you should get it instantly. Well, maybe in 2 short sentences. At most.
Still don't get it? Ok. There's a reason that they call it "Pixel-Peeping".
Take your 800MP pano and look at it at 100% on your monitor. What do you see?
What is the linear resolution of your monitor?
Oh might as well finish this out.
If you followed the above procedure, you are now viewing an 800MP image at between 72 and 120dpi (depending on your monitors' linear resolution) at a viewing distance of about 1ft. The print in question is 800MP on 20m for a final linear resolution of 50dpi.
If 20m on a side, 800MP produces a 50dpi print and 200MP produces 25dpi. Neither are high enough to really show the full-detail of the image until you get out to about 6x normal viewing distance (a 50dpi print held at 6 ft or 2 meters would correspond to a 300dpi print viewed at 1ft). Putting your nose right up to the image would mean that you are too close to see the fine detail, regardless, thus if you did that you wouldn't, couldn't see a difference between a print of 800MP and a print of 200MP. Correspondingly viewing the 800MP 20m image at 2m viewing-distance would make the effective linear resolution 300dpi, but so would moving out to 4 meters for the 200MP print. It doesn't make a difference, it's all a matter of viewing-distance. No matter what, the 200MP image will have half of the detail of the 800MP image but neither are nearly enough to optimize IQ for a 20m print. Upsampling the 200MP image to 800MP would merely halve the effective viewing-distance at 300dpi. If it's done well, there would be negligible IQ difference at viewing-distances outside of a few meters.
You might even get better use out of the 20m print if you just print 200MP of image-data on it at 25dpi.
If you want 600dpi effective you have to halve the viewing-distances above.
Printing the required 36GP of image-data on the 20m print to make it 300dpi at 1ft viewing distance would take forever, not to mention of course you'd have to shoot the pano to that resolution, then render and move the file.
The thing to remember is that not only do you not need to see every nut, bolt and screw in the image, you also aren't going to look at a 20m print at 1m viewing distance or less unless you're walking right by it. The optimum viewing-distance might be somewhere around 10m. Around that point, whether it's 200MP or 800MP or 1.6GP or 16GP won't matter. Much beyond that, no one will care about the print resolution.
The end-result is the same. You can drive yourself nuts worrying about "IQ" to no practical effect if you don't characterize the display environment and get reasonable limits on the required resolution.
PS if I'm wrong, which is possible, I'd appreciate an explanation of why, something technical not just a "you don't know what you're talking about" kind of response. That doesn't help anyone.
PPS personally I don't see much of a resolution improvement beyond 600dpi at 1ft but that's just me, some might argue 1200dpi. For a 20m pano print @ 600dpi at 1ft you'd need around what, 150GP? Is any of this making sense, yet? Render it at 200MP or 800MP either way it's still well below optimal for a 20m print.
"Take your 800MP pano and look at it at 100% on your monitor. What do you see?"
independant - completely independant - from your monitor´s resolution you see 1:1 what´s the quality of your image. The crops i showed before are 100% crops from the whole image. No matter how big an image is - 3mpx or 5gpx: a 100% crop ALWAYS shows the real, native resolution 1:1. That´s why it´s called 100% . . .
If you want something you´ve never had, then you´ve got to do something you´ve never done.
"PS if I'm wrong, which is possible, I'd appreciate an explanation of why, something technical not just a "you don't know what you're talking about" kind of response. That doesn't help anyone."
That´s complex. Several people here already tried to show the direction to you. As i suggested before: learn. Buy some books about image-editing and printing. Use Google to find out about the relations of pixels, dpi, the meaning of the term "resolution" and sizes. Viewing distances are not of great intrest: you never know them when creating and printig an image. You´ll never how close an image will be looked at - despite you can be sure it hangs high up on a wall and so on.
The only relevant thing is: is the 100% crop of good quality? Is it sharp and detailed? Do i see CAs? Do i see noise?
An exellent result you have when the 100% crop is like the ones i showed with the tribune or the oval building. An acceptable result is when it looks like the crop of the stadium´s picture - because it´s shot analog it shows film-grain of course. These pictures being printed in their full size mean to be looked at a distance which is related to the print-resolution. Bigger than A2 nobody prints an offset-print @300dpi. The 300dpi standard in offset printing results - very simply said - from the ability of human´s eyes to see 300 dots per inch as acceptable way to print without being irritaded by the dots when the print is viewed at the lenght of an arm.
BUT: you MUST seperate the resolution of a photography from the resolution it´s to be printed. We have a PICTURE-resolution and a PRINT-resolution. To print a 20m picture using a PRINT-resolution of 55dpi you NEED a PICTURE-resolution of some hundred megapixels.
There is NO WAY AROUND THAT. If you don´t HAVE a high-rez picturefile . . . . then you have a problem. You NEED the pixels to "fill" the space of 20m wide print @55dpi print-resolution.
Imagine it as a mosaic: to make a mosaic of 20square-meters you need a certain amount of parts to fill the space. When you take bigger parts you need less parts - when you take smaller parts you need more of them. If you take the bigger parts you see the mosaic in an acceptable way only from a longer distance. If you take the smaller parts you see the mosaic detailed at a shorter distance. You see more details not only because of the shorter distance but also because there are more details possible to lay as a mosaic using small parts instead of big parts.
Basically it´s very simple - IF you realize the meaning of "resolution" itself. "Resolution" in terms of printing or displaying means not the same things as "resolution" means in terms of photography resp. image-processing like pano-making.
To shoot 200 pictures for a 400mpx pano is the same as shooting ONE picture of 400mpx - IF you know how to do it. In fact it has advantages to shoot 200 pictures instead of one : 1) there´s no camera to shoot ONE picture of 400mpx digitally. 2) if there is one to come - it will be very, very, very expensive. 3) the lens: to "feed" a crop-dslr or a ff-dslr with exellent optical information there are some very fine lenses in the world at resonable prices. To "feed" a 400mpx camera with exellent optical information would mean to have a lens filling a much wider circle with the same optical resolution like the dslr lenses must do.
I know only some special-made lenses in the world which might be able to do so. look here: http://www.gigapxl.org/ They have a custom-made lens placed i an aerial-camera and produce absolutely stunning analogue gigapixel pictures on aerial-recon film
If you want something you´ve never had, then you´ve got to do something you´ve never done.