Hey everyone,
I'm shooting RAW on a Nikon D80, and scaling the images up slightly to get the size and dpi that the print shop I am using recommends. I'm not using any third party programs to scale up... just bumping up to the size and dpi I need in photoshop (CS2).
My question is, is there any benefit to scaling up by an even percentage as opposed to a percentage that might not adjust the pixels evenly? I think I remember reading somewhere that when scaling up or down, you'll get a better image if you scale up by, say 50% rather than 48%. Obviously the resulting image size is going to be very similar, but does photoshop handle the addition of pixels in a way that will make one image better than the other?
As an example, the D80 creates an image that is 3872x2592 which translates to roughly 8.5" x 13" at 300dpi. I'd like to make that a bit larger, so I scale up by 150%, giving me an image size of roughly 13" x 20" at the same dpi, the minimum for the lightjet printers I'm using. The end result is an odd size.... 12.96" x 19.36", but that doesn't bother me, and the number of pixels added is a straight forward 50%. In this example, I guess the question is, is this 50% scale up going to give me a better image than if I'd just plugged 13" into the window and let it scale it to 51% or whatever that difference would be? On the one hand, it makes a certain logic to me, adding one pixel for every two results in a pretty simple process, but on the other hand, were talking about millions of pixels, and there is some heavy duty processing going on anyway, so what does photoshop care if it's increasing by 150% or 151%?
Also, I am wondering about the advice the print shop gave me.. Everything I've read on here says that when scaling up, it's better to go in small jumps, so the first couple tests I did, I used a couple of 120% increases rather than one at 150%. Perhaps even three, with the last one being a small step up, to get to a size I wanted. As per some advice, I also did some sharpening between those steps, but found that the resulting image had way too much noise. When discussing this with the shop, their "printing expert" who has a very good reputation around town, after asking what kind of camera I'm using, said "Oh... that camera has plenty of bit depth. You can just scale up in one step, no need to do it the hard way... then just sharpen a little after that, if you think you need it. I probably wouldn't even bother.." Then he also recommended that I might want to bump the images up as high as 400 dpi. I came to digital from a medium format background, and I would love to get that kind of detail, but doubling the number of pixels makes me nervous... I'd prefer to be a bit less detailed if it means adding 50% less artifacts or noise.
So... now I'm wondering, does this guy know what he's talking about, or is he just blowing smoke? And what's with the "bit depth" thing... The pixels have a depth of 8 bits, same as every other SLR, right? How in the world would one camera's 8 bit pixels have more "depth" than another to scale up better or worse?
I went into this thinking I'd done enough reading to have at least an idea of what I was doing, and would be able to learn the rest as I went, but now I'm wondering if I even have a clue! or maybe if I should just find another printer...
Thanks for the help!
Stephen
