Enlarge 8MP to 2.3m x 1.5m (spinoff from Digital is Dying)

[tonycollinet]

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.jpg

This 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.

[andrew_s]

I've always regarded the 300ppi gold standard for prints as being over zealous.
When I first started playing digital, 3mpix was state of the art for an affordable point'n'shoot. I found that an A4 print would stand putting up against the end of my nose, almost  (I'm short sighted enough to still be able to focus at that range), and that the limiting factor wasn't the sensor but the quality of the lens.

On that basis, 6Mp is enough for a closely inspected A3 print, and if it's on the wall being looked at from two or three metres, it would be OK for poster size.

The main advantage of more Mpix is being able to crop out a smallish part of the whole frame and still produce a decent-sized print. This does assume that the lens and your technique is up to the job.
I regret the marketing pressures that are pushing the pixel values of small pocket-size cameras so high - up to 14 Mpix currently. I'd much sooner have 6-7 Mpix and actually have something that was usable at an ISO much above 200 without the noise reduction smearing out all the detail.

[tonycollinet]

. I'd much sooner have 6-7 Mpix and actually have something that was usable at an ISO much above 200 without the noise reduction smearing out all the detail.

Agreed - I've always thought that compact digital cameras maxed out at 6MP. Certainly 8 should be a limit. The one I use at the moment is 6.

[mike]

the review of the panasonic LX3 on DPreview is quite good, they compare it to the canon 10d and nikon equivalent, the panasonic has 'only' 10MP compared to 15ish for the canon and 13.5 for the nikon, it compares very well on noise, even if it doesnt have quite the same crop-ability.  It looks pretty good up to 400, and certainly useable much higher.