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Pixels Per Inch For Print

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You’ve taken a neat shot and, naturally, want to produce equally big a print as possible to display. But how tin you know just how big y’all should make it?

Before nosotros look at the main factors affecting this determination, information technology’s important to clarify the terms ordinarily used to describe image resolution and so y’all accept a clear concept of what they hateful and where they are applied. Understanding these different measurement metrics volition aid you to sympathize when to use them, and give you some insight into how digital prints are produced.

Jargon buster

Many people are unclear about the differences between pixels per inch (ppi), dots per inch (dpi) and lines per inch (lpi).

Pixels per inch (ppi) is used specifically to define digital image resolution. Each pixel represents a unmarried hue (colour), saturation and lightness value for a single indicate in the image at a vertical and horizontal coordinate.

Dots per inch (dpi) represent the smallest physical size of the ink aerosol produced by a printer on the output media (paper). Multiple dots are needed to reproduce a single pixel value.

Lines per inch (lpi) are used to define resolution for printers that are incapable of continuous tone printing. The term is sometimes substituted with line frequency, screen frequency or halftone resolution and covers rows of cells or arrays of smaller dots that brand up a single tone.

Factors influencing print quality

ane. The resolution of the image. Best results are e’er obtained when images are recorded with the highest image resolution and quality settings the camera provides. For any image, you can piece of work out how big it should exist printed using the pixel density in the print; in other words, the number of pixels/inch (ppi). (Inches are used to simplify calculations.) But first you lot need to know the printer’s output resolution.

ii. The printer’southward output resolution. Whereas digital images are fabricated up of detached blocks of colour known as ‘pixels’ the images produced by inkjet printers are produced by placing tiny dots of ink onto the paper. Photo printers typically use between half-dozen and ten different hues and tones to reproduce colours and many ink dots are required to produce the hue and tone that corresponds with each pixel in the epitome.

All printer drivers contain RIP (raster image processor) software that describes the placement and size of the ink dots on the output media. The printer driver takes intendance of how the dots are really laid down and ordinarily limits the resolution it volition handle to friction match the output capabilities of the printer’southward printing head.

If the ppi resolution of the image sent to the printer is too high, the image will be interpolated down (downsampled) and paradigm data is lost. If the epitome PPI is too low, it is interpolated upwards and at that place’south a real take a chance of interpolation artefacts (typically moirø©, banding and jagged edges) beingness introduced. For the best results, in that location should be a one-to-one correspondence between image ppi and the printer’south dpi setting.

3. Viewing distances and the limits of human being vision. Human vision is good simply it has its limitations. The average human eye cannot discern differences in resolution at output resolutions higher than about 350 pixels/inch with close examination.

However, the further you move back from the print, the less fine particular y’all are able to see, even in optimal lighting conditions. Consequently, it’south possible to reduce the output resolution without viewers seeing an obvious deterioration in prototype quality.

Practical applications

A typical photo inkjet printer provides a linear resolution of up to 1440 dpi, which means it can lay down 1440 droplets of ink in each linear inch of newspaper. These dots must be bundled into cells to reproduce the continuous tones in a digital photograph. Larger cells can contain more tones while smaller cells provide greater detail, so there’s a trade-off between colour handling and output resolution.

A popular rule of thumb says the optimal paradigm resolution for press at the most common output sizes should be 300 ppi. Using this rule, dividing the image resolution by 300 will tell you roughly how big you should make prints at snapshot and A4 sizes. (We’ll bargain with larger output sizes afterwards.)

Below 300 dpi resolution begins to fall off although, depending on the printer yous apply, you probably won’t run into much departure in print quality between 250 dpi and 300 dpi without a magnifying loupe. At normal viewing distances these differences will probably be invisible so we’ll classify all resolutions to a higher place 250 dpi every bit ‘Excellent’.

If you utilize an viii-megapixel photographic camera with a 3:2 aspect ratio, it should be possible to produce fantabulous borderless A4 prints at 300 dpi. The calculation works as follows: Split the longer side of the epitome pixels (3504) by the length of the A4 sail of paper in inches (11.69 inches). The event is 299.74 dpi, which is almost 300 dpi.

The same calculation used on higher-resolution images demonstrates that all cameras should be capable of producing first-class quality at output sizes of A4 and smaller. In fact, when printing at snapshot size, images from files larger than 1800 x 1200 pixels need to be downsampled.


Serious photographers like to brand poster-sized prints of their all-time images. The same calculations can be used to estimate maximum output quality, taking business relationship of the average distances from which different-sized prints are viewed.

Many photographers adopt to make larger prints with a white border effectually the image. The width of this border relative to the paper size is a thing of individual taste, although in most cases it’s at least an inch on each side.

The table below outlines the resolutions and output quality ratings for two popular enlargement sizes, allowing for a one-inch border forth each shorter side of the image. Information technology demonstrates clearly how different megapixel counts in digital cameras volition support dissimilar degrees of enlargement.

At 180 dpi and lower output resolutions, there will be a noticeable loss of particular, especially in highlights, and dissonance will be credible in adumbral areas. This level would exist classified as ‘Poor’ print quality.

Between 180 and 250 dpi there’s a grey surface area nosotros have classified as ‘Expert’. At the lower end of the scale, prints made with resolutions between 180 and 200 dpi may contain some artefacts in detailed areas but they probably won’t be visible in large prints at normal viewing distances.

In a higher place 250 dpi, images volition be good plenty to withstand scrutiny at normal viewing distances. And so what’s the ‘best’ viewing distance for enlarged prints?

Mostly speaking, people naturally tend to take ii standpoints, the first at a distance where they can comfortably take in the whole moving picture, and the 2d closer in where they tin can run into details. The distances vary with individuals, but most people stand farther abroad from larger pictures and closer to smaller ones.

In applied terms, there’s a trade-off between impress resolution and viewing distance. The table to the right shows the minimum resolution at unlike distances before the eye begins to see individual pixels in prints.

This explains why photos on billboards tin be printed with very large dots, yet announced as continuous-tone images at the right viewing distance.

Other factors

Several other factors can influence how much an image should be enlarged. For landscapes, the center normally expects to see detail to virtually its resolving limit, whereas images that bear witness smooth surfaces and geometric structures can be less demanding.

This means you should be conservative when calculating how big to print landscape shots but volition probably accept more flexibility when printing photos in which the resolution of detail is less of import. However, some regions in the less demanding subjects require ameliorate item resolution than others. For example, hair and eyes in portraits unremarkably need to be fully resolved, although skin can often benefit from some softening. These problems are usually addressed while editing shots, which are then printed for maximum resolution of the detailed areas.

The optimal viewing distance for images may also be influenced past textures inside a photo and/ or the paper on which the prototype is printed. Detailed images usually look best (and can withstand closer inspection) on papers with shine surfaces, whereas softer-looking shots can often benefit from being printed on textured papers and viewed from distances where the texture of the paper will complement the image.

Detailed images are also more likely to exist subjected to close inspection because viewers usually desire to scrutinise their intricacies. In contrast, it’s usually more satifying to view soft and lengthened pictures in their entirety to obtain an impression of the photographer’due south intent.


Attribute ratio cropping

Borderless printing is only possible with some printers and ordinarily involves cropping the image to fit the paper. Images with a iii:2 aspect ratio should fit entirely on a snapshot-sized impress, whereas 4:three aspect ratio images will be cropped.


Images taken with a three:two aspect ratio should fit entirely on a half dozen x four inch (15 x 10cm) snapshot-sized print.

Cropping is inevitable when you print on nigh popular newspaper sizes and some printing software allows you to preview the cropping before committing to a print. Images with a 4:iii aspect ratio are cropped along the long sides, while those with 3:2 and 16:9 aspect ratios are cropped at the shorter sides. The blood-red outlines in the illustrations beneath show the areas cropped with different aspect ratios.


Cropping a 4:3 aspect image.


Cropping a 3:2 aspect image.


Much more of the image is lost when a 16:ix aspect image is cropped for borderless printing.

When you want to preserve the entire image, you must allow for borders around the print. On A4 newspaper, the tiptop and bottom borders will exist wider than the borders along the brusque sides of the image.


This illustration shows one way of positioning a panoramic image on a canvass of A4 newspaper to avoid cropping and let an attractive framing layout.

This is an excerpt from Photo Review Result 56.

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