Nov 30

Printing JPEG

Posted by Benedikte Vanderwee├źn on 30/11/2008

Recently, a client asked me what type of digital camera he should buy. The most important feature he wants is the ability to print his JPEG’s in print quality. He wants to use his photo’s in printed brochures, printed newsletters, advertisements, etc… The question here is: how do you know on what dimensions you can print your digital photo?

Maximal resolution of your digital camera

I responded that a few things are really important when buying a digital camera and use the digital photo's for print. First of all: the maximum image resolution (in pixels) of the camera is really important to know the maximal size you can print your photo. This depends on the amount of pixels your camera can store in an image. The amount of megapixels your camera has, will define the pixeldimensions of your image. See below in the table what amount of megapixels your camera need to be able to print a desired format. I explain this with an example:

  • my photo's need to have a print resolution of 300 dpi (dots per inch), some say 200 dpi is sufficient. I calculate with 300 dpi.
  • we have a photo with a pixel resolution of 1200 pixels width on 797 pixels height
  • divide 1200/300=4 and 797/300=2,65. Attention: these are the sizes in inches, we have to convert them to cm
  • 4 inch x 2,54 = 10,16cm (1 inch = 2,54 cm) and 2,65 x 2, 54 = 6,74 cm
  • the maximal dimensions for print for this photo are 10,16 x 6,74 cm

Calculate the maximal print size

Here is a list of the things you have to take into account before delivering your digital photo's for print:

  • you have to know the (maximal) dimensions of your photo in pixels
  • this is the formula: number of pixels (width or height) / relative resolution (300ppi) x conversion factor(0,39) = dimension in cm (1 cm = 0,39 inch)
  • in reverse, you calculate the pixel dimensions needed for a certain output dpi as follows: relative resolution (300ppi) x cm x conversion factor(0,39) = numbers of pixels

Use Photoshop to calculate

Now that we understand the calculation behind the different resolutions, we open Photoshop or any other photo editor and let the program do the work. I open a photo and choose Image > Image Size and see this:

image at 72 dpi
  • Pixel dimensions: Width: 3872 pixels and Height: 2595 pixels
  • Document Size: Width: 136,6 cm and Height: 91,44 cm (choose cm) and Resolution is 72 pixels per inch
  • 3 checkboxes below are checked by default!

We want to know the maximal print size of this picture at 300 pixels per inch.

image at 300 dpi
  • deselect the last option of the checkboxes: Resample Image!This is an important step because we don't want to loose any pixel information stored in the image. Notice that you are no longer able to adjust the pixel dimensions of the image.
  • Change the Resolution of the picture from 72 to 300 pixels per inch, or the resolution you want, you will see that the document print size will change accordingly
  • Document Size: Width: 32,78 cm and Height: 21,95 cm. This is the maximal print size of the picture at a resolution of 300 pixels per inch.
  • let the other 2 checkboxes below checked

Check your camera first

So, before buying a digital camera, check if the maximal image dimensions are sufficient for the print dimensions you want.

Here you find a short list of the amount of megapixels of your camera and the maximal print dimensions at 300 dpi:

Camera resolutions and print sizes:

megapixels max.optical resolution (pixels) printdimensions in cm at 300dpi
2 1600 x 1200 14 x 10
3 2048 x 1536 17 x 13
4 2272 x 1704 19 x 14
5 2560 x 1920 22 x 16
6 3072 x 2048 26 x 17
7 3072 x 2304 26 x 20
8 3264 x 2448 28 x 21
10 3648 x 2736 30 x 23
12 4000 x 3000 33 x 25

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