As promised in the Why Digital is Dying thread - an example of an 8MP image enlarged to print at 2.3 meters x 1.5 meters (all dimensions approx, and sorry for the mix of metric and imperial in the following). I have decided to put it in a new thread, so we can discuss the validity or otherwise of the process here, rather than mixed in with all the other issues associated with that thread.
Prompted by WDiD, and the samples from
NYPHotographics here (also posted to WDiD), which show 3MP images upsampled and printed at large size, I wanted to see what would happen if I tried the same with one of my images. I've not spent a great deal of time on this, and I am sure with more care, better results could be obtained. Most of the time was spent finding out how to to a "stair intermpolation" in the Gimp, as he used in photoshop.
Here is the full image - resized, so you can see it here.
The original is sized 3519x2345 pixels, taken with my 20D and 70-200L lens. It had already been converted to jpg from raw, and sharpening has been applied. As stated above - if I was going for utmost quality, I would take more time, start with the raw image, and go from there.
here is a 100% crop of the eyes of the monkey:
At this resolution, printed at 300dpi, the image would be aprox 12x8 inches. The uncompressed file size is aprox 25Mb
Next I resized the image. Using stair interpolation (basically uprezzing a small amount at a time untill the required size is found - I used 10% steps - I also used linear interpolation for each step for speed) I increased the size of the image to 9000x6000 pixels. Now the uncompressed file size is 162 MB. I applied sharpening (unsharp mask), and increased contrast using curves.
This image, now printed at 300dpi would be roughly 30 inches x 20 inches. But I want 3 times those dimensions. So I am going to print at 100dpi (Shock Horror). Well why not. In order to see a 90 inch (2.3m) wide image without needing to move your head too much, you need to stand about 2.5 meters away. At that distance, each pixel at 100dpi will appear less than half the size of your pixels on the 300dpi 12x8 at 30cm.
Here is a crop of the eyes at 100%. Not embedded, because the forum software shrinks it.
http://www.collinet.plus.com/photos/eyes_large.jpgThis crop roughly fills my 21 inch widescreen monitor, coincidentally
at 96dpi. So when I look at the eyes on my monitor, they are aprox the same size as they would be on my 2.3m wide print. If you can, get this picture on a similar sized/resolution monitor. If you think it doesn't look good enough sat 18 inches away, then try standing back about 2.5 meters. Now imagine that quality over a 2.3m wide print.
Looks pretty good to me at that size.
As an aside, to see the detail you are getting, here is a 100% crop showing the monkeys palm print, just below the bark he is munching on.