Scale Images with the Print in Mind
So let's talk a little bit more about this thing called printer native resolution. Now, every printer has a native resolution. What does that mean? It means that they like a certain ppi that they like to receive when we send information to the printer. For Epson printers it's 300 pixels per inch, and for Canon and HP printers it is 300 pixels per inch. So, if I have an image on my screen and I have it's size, say, at 250 ppi and I send it to my Epson printer, the printer will automatically interpolate that information. It won't change the size, but it will interpolate that image density, or pixel density if you like, to 360 ppi. It will make the interpolation for you, and you'll get the print. I personally like to be in control of that process, and like to send the printer a native resolution print which is gonna give me optimum results each and every time. Let's look at resizing images for print. As we said earlier in this course, as print size comes down the resolution simply goes up...
, because we are spreading the pixel count of the information that's been captured by your sensor simply over a larger area. So, when we look at the sizing dialogue here in Photoshop. So, if we have 10 inches width by 8 inches in height at 300 pixels per inch, when we go and change that resolution to a 5 by 4 image we then get a 5 by 4 with a resolution of 600 pixels. Don't worry too much about the maths, trust me it works, this is how it works. The smaller you get and the resolution goes up. Now, what happens though, in situations where we don't wanna print at 600 ppi. We don't want to send information to the printer at we want to send information to the printer at 360. That basically means what we need to do is throw some pixels away. Always, always, always, we work with a master file, and that master file is never cropped. It is never changed. We make a duplicate of that master file when we go to print. So if we do, ever, want to downsize an image to something like that is gonna be this small, and we are throwing pixels away of course. Then we are not damaging the chance of ever going big again because we're throwing the pixels away and we can't get them back once they're gone. They are gone. Now, if on the other side of the coin, if I wanna make the image bigger. So 11 inches by 14 inches, and I'm keeping that ppi, all those pixels the same, I'm gonna end up with a resolution of 214.286 pixels per inch. So, less pixel count. In other words, the pixels are spread over a greater area. In this scenario here, though, we need a resolution of 360, or 300 if you're printing on Canon to send to the printer. We need to add more pixels, or make up some information. That process is called interpolating. Later on we're going to jump into Photoshop, and we're going to show you exactly how that works. When you upsize, you're interpolating an image, okay, and that can lead to all sorts of problems, if it's not done correctly. The million dollar question, always I get asked by photographers who are very, very passionate about printing is this one here: How big can you go? How big can you go? Well it depends on a lot of factors. Number one it depends on the resolution of your camera and how many pixels you have captured. But also, when you start going big and you start to push that pixel count, and you start to make up information through the interpolating process through Photoshop, we end up with a couple of different problems. The biggest one being image softening. So what we thought was sharp, the minute we start to add pixels or make up information through the very complex algorithms that Photoshop has to make up that information and make it look seamless, we're gonna lose image detail. Also, where we have sharp lines, we're going to get a phenomena called stair step patterns. In other words, what's a straight line as we start to make up information and stretch that line, you basically start to get little steps. Obviously sometimes you're gonna start to get noticeable repetition patterns. The way the algorithm works in Photoshop is, like I said, very very complex. Basically it analyzes the pixels and then as the image gets bigger, it tries to make up pixels that kind of fit that area to make it look like those pixels were always there. It does a very, very good job, provided that you don't go to a stupid size that your sensor can't handle. In other words, shooting with a six megapixel camera and expecting an 80 inch print out of it. It's really not gonna happen. Not at that sort of resolution that we want to print photographically. When we are resampling up we are interpolating new pixels. It's okay up to a certain point. Then there is a point where it isn't okay anymore. We are resampling down, you are throwing pixels away. Interpolating, big and resampling, down, throwing away pixels. Now, resampling should be done at the beginning of your printing process. So you have your master file with the native resolution of the file, and with either Camera Lightroom or Adobe Camera Raw, we've set that resolution of our file because if we are working in an Epsom environment, it is 360 dpi which is what the printer wants. Of course the Canon would be a 300 dpi work flow. So we have set that in stone. If we are resampling to go bigger, you know that is definitely done at the printing stage and we're not gonna mess around with that original file. So before any final adjustments, like sharpening and contrast are made, that's when you upsize up or down. In other words, we don't sharpen the image before we upsize. Why don't we do that? Well simply think about it this way. If we have already lines that have been sharpened, then the minute we start to make up information, then that sharpening is really gonna be all over the place because those lines aren't what they used to be. New information has been added and this is why sometimes with interpolating really big, you have to then evaluate contrast again and we have to evaluate print sharpness. The last bit of sharpening that we do is the very very end, before it goes to print. And once again, once I jump into Photoshop, you will definitely be able to see how we do that. And the different ways of sharpening too. Print resolutions verses viewing distance. I guess one important factor that affects your perception of the quality of the print is the viewing distance. Like with prints that are fairly small in size or prints that you hold at arm length, then using something like the 300, 360 dpi is what we expect. But then when we look at a billboard, when you look at billboard and the dpi count on that is probably something like 10 pixels per square inch. So if you look at it really close, you can't even make out it's an image. But from 200 feet away, it looks like a continues tone image. So the dpi is going to fit on obviously how big you go, but also on the size that you print. I love watching photographers that look at really really massive prints and they go up to them this close trying to look at them. That's not normal. You shouldn't do that because if the print is big, if the print is big then it's meant to be enjoyed from a far distant. That's why you enjoy prints on a larger scale. Large scale prints, they're meant to be viewed at a distance away, not up to here at arms length because it just doesn't make any visual sense for you to be drawn into that image. And compositionally, everything that compositionally works for that image is not visible here, but it's going to be visible from way back there. It's all relative of course. So small prints to be viewed close up need a high resolution because of finer details are going to be visible. And large prints like billboards viewing distance is so great that the detail will definitely not be visible so it doesn't matter if we print them at a far far lower resolution.