Tech bytes for tea?

First decide what size the photos are to be printed out and crop them based on the corresponding aspect ratio.There are a number of standard sizes that photo shops print in. I have tabulated below some of the traditional sizes together with their physical dimensions in millimetres and inches.

For each of the standard sizes, some shops print variants of the standard dimensions to cater to varying aspect ratios. For example, although traditional 4R has an aspect ratio of 3:2, some shops give the option of printing similarly sized prints at 4:3 aspect ratio.

The resolution of a photo is the number of pixels per inch (ppi). To work out the number of pixels a photo should have, multiply the physical dimension in inches by the desired image resolution.

For example, a 5R print is 5 x 7 inches. Multiply by 300 ppi and your image should, therefore, be 1,500 x 2,100 pixels.

For optimal quality, use an image resolution of 300 ppi. For printing on a personal printer, 150 ppi is usually good enough, although some studios accept resolutions down to 100 ppi. Since all my prints are 4R in size, all my images are at 300ppi. This way, they are optimal for 4R and still good enough if I want to print up to A4 size.

Note that studios usually crop a small margin of up to 3%  around the photo. The cropped margin could be bigger on one side compared to the other. This is usually unnoticeable for most photos. Unless the subject is really tightly framed, in which case part of the anatomy, say a ear or finger-tip could be cut off the edge.

However, if your photo has a decorative frame or border that you’d added using a photo-editor, it will turn out uneven. Choose a studio that can crop the photo evenly all round. I find it easier to show the studio a sketch to illustrate when explaining.

Likewise, when using your own printer, it pays to do a few test prints to determine the right settings for even borders.

Standard print sizes, aspect ratios and optimum/minimum image resolution for printing.

Print Size	Size (inches)	Size (mm)	Aspect ratio	Optimum Resolution (300 ppi)	Minimum Resolution (150 ppi)
3R	3.5 x 5	89 x 127	7:10	1050 x 1500	525 x 750
4R	4×6	102 x 152	2:3	1200 x 1800	600 x 900
5R	5×7	127 x 178	5:7	1500 x 2100	750 x 1050
6R	6×8	152 x 203	3:4	1800 x 2400	900 x 1200
8R	8 x 10	203 x 254	4:5	2400 x 3000	1200 x 1500
S8R	8 x 12	203 x 305	2:3	2400 x 3600	1200 x 1800
10R	10 x 12	254 x 305	5:6	3000 x 3600	1500 x 1800
S10R	10 x 15	254 x 381	2:3	3000 x 4500	1500 x 2250
11R	11 x 14	279 x 356	11:14	3300 x 4200	1650 x 2100
S11R	11 x 17	279 x 432	11:17	3300 x 5100	1650 x 2550
12R	12 x 15	305 x 381	4:5	3600 x 4500	1800 x 2250
S12R	12 x 18	305 x 465	2:3	3600 x 5400	1800 x 2700