Printing photos may look like the easiest job in the world, but it is quite a bit more complicated than it seems. Unlike the general idea, printing is not just about selecting an image and hitting print. A lot of careful details must go in to the pre-press structuring.
Learning about resolution is an absolute prerequisite, as is knowing how to print an image without lowering its quality. Editing an image and sharpening it to give off a crisp look is also an important part of printing.
Resolution: What exactly is it?
Understanding image resolution can be a little tough. Resolution is basically the total number of pixels which are displayed per unit of a printed picture’s length. It is the standard measurement used when printing any image, and is expressed in terms of the unit dpi (dots per inch). The whole idea revolves around how printers print an image composed of tiny little dots. When a picture is viewed on a screen – say a TV, or a computer monitor – the resolution of the image is measured in the unit ppi (pixels per inch). This all makes sense because all digital images are made up of tiny pixels, which are basically individual little blocks of different colors.
The concept of resolution and pixels merge because for any picture, how close its pixels will be packed together depend upon the picture’s resolution measurement. The higher the resolution of an image, the more tightly packed the pixels will be, thus guaranteeing a smooth, high quality print. Similarly, a picture with low resolution will loosen its pixels, thus reducing its print quality.
How much resolution is needed?
The printing device decides whether a picture needs a higher or lower resolution. For example, consumer inkjets churn out pretty good pictures at 225 to 250 dpi. When it comes to black and white laser printers, 150 to 200 dpi is considered optimum.
To figure out for yourself how much resolution is appropriate for your picture, open up the image in Photoshop, and try this out:
1. With your selected image open in front of you, navigate to Image > Image Size. Say, for example, the image that you have chosen is around 14 mb’s, at 72 ppi. It is a pretty high quality image, having pixel dimensions of 2716 x 1810. That is a whole lot of pixels, which would mean to print an image of this size at its current resolution, a paper around 25 inches in height and 37 inches in breadth would be needed.
2. From the bottom of the Image Size dialog box, go to Resample Image and uncheck the box. What this does is lock the pixel information, thus sealing image quality.
3. Now, if you enter 300 in the Resolution Box now, the actual size of the image will change to around 9×6 inches, thus preserving the image quality by scaling the picture. But if you look at the Pixel Dimension option at the top of the dialog box, you can notice that the change in resolution has had no effect on the pixels – they remain the same. Thus, this option simply alters the resolution of the image without changing image quality.
Sharpening an image
After deciding on the resolution, the last step is post-processing. Suppose a picture has sufficient resolution, but is a little blurry, and you want to print it – what do you do? While you cannot magically make it totally clear, here is what you can do to improve it as much as possible:
1. Sharpening an image in Photoshop is not just about boosting contrast along the edges, it also needs to have a proper tonal range adjustment. To do so, adjust the sliders in the Curves/Levels tab (you can find it in Image > Adjustments > Curves/Levels).
2. Next, a new Curves Adjustment Layer has to be created, and the contrast has to be adjusted using points on the tonal curve. Ultimately, sharpening is all about contrast.
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