What should be the Resolution of your Image?

One the most common confusing part in photo editing is that not understanding the resolution, what is it and on what purpose what resolution should be used. To get a better a answer of these questions first we need figure out on where we are going to use this or what is the final output of the images such as if they are for printing or only for your desktop screen of your monitor or cell phone or for some sort of tablet device means digital display. We can also be more specific means if they are for printing then where they will be printed in a printing press or in your inkjet printer etc. Because the resolution depends on these selections

There are three different categories of output: one is halftone output, second is the continuous tone output and the third is the display output. To understand resolution we have to understand each of them because each of them needs different resolution.

The Half Tone Output

Half Tone is used in the printing press for reproducing images with an illusion of continuous images. For a black and white picture it is just different sheds of black and white dot pattern and for a color pictures it is also dot patterns of for color of CMYK series. So everything those are for printing first needs to be converted in half tone. Now what should be the resolution for these printed output or half tone output on other word? There is a common term used in printed media which is “line screen”. Line Screen is the number of half tone lines used per inch. It is often expressed as “LPI” lines per inch. Without going deep simply line screen depends on the paper quality and the printing press. You may not know what line screen you are using. But there is some default standard of line screen value. The general thumb rule for selecting resolution is that resolution will be the as twice of the line screen. The default line screen values for some area are as follow:

• For Newspapers/publications which are printed on newspaper use a 65 or 85 lpi.

• For Books printed on uncoated stock use a 120 or 133 lpi.

• For Books and magazines printed on coated stock use a 133 or 150 lpi.

• For High quality books with lots of graphics on coated stock will use 150 or higher lpi.

You may not know what line screen you should use but you know what kind paper you will use for your printing such as glossy paper stock, matte stock etc. Each types of them have a recommended line screen. You will know them form the printing press. Once you know the line screen then your resolution problem is solved. Just double your line screen and you will get the resolution.

We used to say that higher resolution means higher quality of image but for offset printing it is not true. For a 100 lines per screen printed media the resolution should be 200 pixel per inch but instead of 200 resolution if you use 600 pixel per inch resolution the quality won’t increase. You will get the same quality print for both of them. On the other hand this high resolution will increase your printing time as you are giving more information to the printer.

The Continuous Tone Output

The continuous tone image is the one where at any point of the image each color reproduce as a single tone. On the other words, the continuous tone image is one where the colors and the grey sheds are merged into the neighborhood color and shed. Where in half tone the color and grey shed are like discrete dots. The example of continuous tone image is the Photographs.

In continuous tone image you don’t need to know the line screen because you are not converting your image into half tone dots. You are printing it as you simulating creating a photograph in the dark room. If you see through a magnifying you won’t see dot’s like printing press. And you can relax about resolution as by default you can keep it as 300 pixel per inch(actually a little bit lower then that but who bother to keep that in mind).

Outputting to a Screen

The third category is outputting image in a screen which can be any size. When you are targeting a display monitor of any then actually you don’t need to care about the resolution. The dot per inch doesn’t matter but things that matter is the pixel dimension of the image. You shout set the width and height of the display area in pixel size as the image width and height in pixel. So the most important thing you need to know is the device dimension in pixels.

Resolution only matter in print but when you targeting it for outputting to a screen then resolution doesn’t matter. You can see it, set the image width and height in pixel and then change resolution you see the image size not changing. It means the quality is the same regardless the relolution.