learning hub

Pixels and Print Sizes

An important factor in print quality is the number of pixels per inch (ppi) used to make the print. The more pixels per inch, the finer the detail in the print will be and the sharper it will look.

What is a pixel?

Short for picture element, each pixel represents an element of a digital image that, when grouped together, create a recognisable picture. In the case of a digital camera, the information for each pixel is gathered by corresponding, light-sensitive ‘photo sites’ arranged on the surface of the camera’s image sensor.

What is a megapixel?

A megapixel (MP) ontains 1,000,000 pixels and is the unit of measure used to describe the number of photo sites on the sensor in a digital camera.

Image File Size?

The file size of an image is expressed by the horizontal and vertical pixel counts (e.g. 3000x 2000 pixels). To find the total number of pixels in an image, just multiply the number of pixels in the width of the image by the number of pixels in the height of the image (e.g. 3000x2000 = 6 MP)

Image Resolution

In general terms, image resolution often refers to the amount of digital information contained in an image file. A picture file size of 4,000 x 3,000 pixels will have a higher image resolution than a file size of 2,000 x 1,500 pixels.

Image resolution may also be referred to as pixel density in terms of Pixels Per Inch (PPI) rather than the size of the whole image file which is much more important when it comes to making photo enlargements.

What does PPI mean?

PPI stands for pixels per inch and refers to the number of image pixels from the digital file that will be used to create one inch on the printed medium - with 300 ppi being the industry standard for high quality printing.
Photos in an album are usually viewed with the photo only 30-40 cm from your eyes so 300 ppi is ideal but if you enlarge a photo to hang on the wall and view from a few metres away you can get away with a lower resolution like 200ppi.
If you over enlarge an image (e.g 100 pixels per inch), then you will get a very “pixelated image” with pixels becoming more evident and jaggies (steps) along diagonal lines.

How large can you print your photo?

Here are the steps to determine the number of megapixels of an image and how large you can print it.

  1. fnd the dimensions of the image (look at the image properties).
  2. divide the width and height dimensions by 300
  3. the answer is the size in inches of the largest good quality print you can
    expect e.g. the 4608x3072 image below will yield a 15 x10 inch.
    A 640 x 480 image would only be suitable for a passport sized photo but as they look good on the customer's phone screen they don't believe us.
example of an image's properties providing the dimensions
This table shows popular photo paper sizes and how many pixels are required to achieve good quality prints.

Avoiding too few pixels

Don't crop at home - let our photo system do the cropping - you will get a warning symbol once you get below the ppi required for the photo size chosen. We can then advise you how to progress and offer alternatives.

If you want to print a photo saved from on-line (e.g. facebook) or one that has been emailed to you we suggest that you order through our system (on-line or in-store). If you get a warning symbol for the photo size you have chosen then choose to print a smaller photo size or email the person that took the photo asking for the original photo that (hopefully) has more pixels.

Sometimes the issue is the wrong setting on your camera - talk to our experts.

Camera settings for high quality prints

You can set your digital camera or phone to record in various sizes from large to small, or quality from high to low.  We recommend that you set your camera on the highest image size (resolution) setting and the highest quality setting (least amount of compression). And then leave it alone... we've had a few customers who changed the setting to take a photo for Trademe then forgot to put it back to the larger size.

Phone settings for high quality prints

Same as cameras - select the highest image size (most pixels) and least compression if option provided. Also use a standard aspect ratio (3:2) if you plan to print and enlarge photos. .

Don’t "resize" an image to enlarge it

You can use the resize feature in photo editors to make an image smaller but DO NOT USE IT TO ADD MORE PIXELS. The software is adding pixels by guessing what the new pixels should look like based on existing neighbouring pixels. In simple terms, the original pixels are spread apart and new pixels are placed in between them to fill the gaps.

When there are "compression artifacts" such as evident blocks due to lossy compression present in an image there is no way of removing them. The detail is lost! "Lossy compression" arises when an image file is compressed to make a smaller file size by throwing information away.

right side of photo has had lossy compression applied

Is DPI the same as PPI?

NO! DPI means dots per inch, and has to do with how much ink your printer lays down when it prints a photograph. Printers with higher DPI settings can produce more detailed photographic prints.

DPI and PPI are used interchangeably a lot of the time, but they are not the same thing.

  • PPI refers to pixels captured in the image
  • DPI refers to dots produced by the printer

 

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