Clive R. Haynes FRPS

Our goal should be ‘photographic quality’. This can be achieved providing attention to detail is maintained throughout the imaging process.

In one respect the definition of a digital picture is very similar to traditional photography – that is, the larger the original image size/information is – the better the printed picture will be.

Size is Important.

My preferred scanning-in resolution for 35mm slides or negatives is 2700ppi (pixels per inch). This scanning resolution will enable me to print an A3 size picture of photographic quality. The resolution of the print at that size will be in the order of 220 ppi. The accepted minimum is around 180ppi. Anything less than 150ppi will begin to look pixelated, especially along curves and diagonals.

Flatbed scanning should be adjusted to give 200ppi if photo-quality results are required at an approximate 1:1 ratio for original to output print. Some experimentation may be necessary to fine-tune your scanner in this respect.

Bearing the above information in mind and with respect to 35mm originals, the following information will provide a guide to resolution and file size.

Scanning at 2700ppi a colour 35mm original will produce some 9,700,000 pixels (9.7mpxl) of picture information and a file size of 20mb to 25mb (the figure does vary). At 200ppi the image will look fine at A3 size. To conserve file size, if the image was intended for no more than an A4 print, again at 200ppi, the scanning resolution could be reduced to produce a file size of 10mb to 12mb. For A5, following the same guidelines, the resulting file size would be in the order of 5mb to 7mb.

Remember, changing the scanning resolution will alter file size and therefor the picture quality of the final image.

If you’re uncertain as to the finished picture/print size, always scan in at maximum. It’s too late to change file size later as for quality the ‘re-sampling’ option is not an answer.

Many excellent digital cameras are now available and 'high end' models such as the Fuji S1 will yield excellent results from an 18mb file, with very acceptable prints of A3 size. However many 'consumer' ‘megapixel’ models will struggle to produce quality images larger than say A4 (a lot depends upon content, your requirements and needs). Never the less, I have seen excellent images produced by models producing around 4mpxl and upwards. There is also a big difference in quality (and cost!) between 'consumer chips' and 'pro chips'. Digital cameras produce texturally smooth and grain-free images, the result of which frequently looks better than scanned-in slides or negs with their inherent grain structure and surface blemishes.