Clive R. Haynes FRPS
goal should be ‘photographic quality’
In one respect the one of characteristics of a digitally-captured picture is very similar to traditional film-based photography – that is, the larger the original image size/information is – the better defined the printed picture will be.
can we actually see?
is 300ppi often referred to as the standard?
a rough guide, cameras with a specification of around 6 to 7mpxls can
be considered the lower limit for acceptable A3 prints. The 6 or 7mpxl
image will become around 18mb to 20mb when opened in the computer.
Most consumer (SLR)
models will yield excellent results from pixel counts in excess of 6mpxl
to 10mpxl. We can determine this by multiplying the nominal pixel count
by a factor of three, as there are three channels (red, green & blue),
give file sizes of (6mpxl x 3)18mb, to (10mpxl x 3) 30mb thus providing
very acceptable prints of A3 size and greater.
What is acceptable is of course subjective and depends upon content and the purpose for which the image is intended.
Quality digital cameras shoot RAW file format and this allows 16 bit working to carry through into 'Photoshop'. For more information about 'RAW' click on the link below.
What if the print we are to make
is larger than the original image?
Bearing in mind the above and with
respect to 35mm originals, the following information will provide a guide
to resolution and file size.
Scanning at 2,700ppi, a colour 35mm
negative or slide will produce some 8,000,000 pixels (8mpxl) of picture
information with a resulting file size of 20mb to 25mb (the figure does
vary). When expanded to A3 size, the image will look fine at around 200
Size is Important.
Remember, changing the scanning resolution will alter file size and therefor have a direct bearing upon the maximum acceptable picture quality of the final image - which shouldn't fall below 200ppi.
If you’re uncertain as to the size
required for the finished picture/print, always scan in at maximum.
It’s too late to change file size later as for quality the option
of ‘re-sampling’ is not an answer. Re-sampling can be done
but it's best treated as a last resort - there's nothing better than getting
it right in the first place.