In this movie, I'll show you how to downsample or reduce the number of pixels inside of an image for print. Now at first, this may seem like a daft idea. After all, if upsampling or adding pixels is a destructive modification, then downsampling or reducing the number of pixels must be doubly destructive, but in fact, whereas you rarely upsample an image in Photoshop, you frequently downsample for a variety of reasons. First of all, let's say we're working in a production environment and we want this image to be 12 inches wide.
But we don't want to hand off this gargantuan file, either to a designer who's going to lay it out in a print document or to a commercial printer because it's going to take forever to upload and is going to waste everybody's time. Instead, what we want to do is downsample the image for the occasion. So here is how it works. Make sure to do all the work that you want to in a high res version of the file and you go ahead and save your work. That's very, very important. Then assuming you're working inside of a layered image, you go up to the Layer menu and choose the Flatten Image command.
It's dimmed in my case because I'm working in a flat file in the first place. And then of course, by the way, you would not resave the file at that point, because you would destroy your layers in a saved image. Instead, you wait a moment to save, and you go up to the Image menu, and choose the Image Size command. Then you can turn on the Resample Image check box so you are changing the number of pixels inside the image. I'm going to dial in a Width value of let's say 12 inches, and then I'll tab down to the Resolution value, and I'll take it down to the absolute highest resolution I really need, which is at most 360 pixels per inch.
But I could take it down to 300 PPI or 267 PPI depending on my destination. Well let's say I don't know exactly what line screen my printer is using, and I've got all these pixels to work within the first place. I'll just take that Resolution down to a conservative 360. Now notice that my file size in RAM is dropping from its original 166 megabytes down to a mere 36 to 37 megabytes here. So that's a big drop. Now I'll go ahead and click OK in order to apply my modification.
Then I'll press the H key so that I can get that bird's eye function, and I'll drag over to this section of the image here. And just look at the sharpness of that detail, and that's a great thing about downsampling. We're not asking Photoshop to make up new detail, we're just asking it to coalesce the original detail inside the image, and often times, the detail ends up looking better because we get rid of noise and other image artifacts. Now at this point, just to make sure you don't harm your high resolution layered file, we would go up to the File menu, and choose the Save As command, and then save the image to a different location, name, or file format.
I'll explain how saving works in an upcoming chapter. Now just for the sake of comparison, I want you to see what would have happened if we had done a similar upsampling from that low resolution version of the image. So here is the low resolution image. I'll go to the Image menu, choose the Image Size command once again and I'll dial in those same values. So I'll change the Width value to 12 inches, and I'll take the Resolution value up to 360 PPI, and now whereas the image was formerly 1.6 megs in memory, it's going to grow to almost 37 megs, I'll go ahead and click OK, and now I'll press the H key and pan to a different location in the file.
I'll go ahead and drag the image with the Hand tool for a moment just to get it into a good location here. And here's the difference. Even though we have just as many pixels inside this image, the details are gummy, if not downright indistinct, whereas, they look absolutely great in a downsampled version of the high resolution file, because we have a much better spatial resolution when we scan or photograph at a high resolution in the first place, and then downsample, than we do if we capture a few pixels in the first place and upsample.
The moral of the story is, Photoshop is not very good at upsampling, but it's great at downsampling, and your decisions about downsampling all depend on the final destination of the image.
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