Simon PM'd me to ask:
Can you please tell me how many MB's on average your drum scans are? My drawing is a little smaller than A4, but the drum TIFF is only 52MB.
I took a quick look through my folder of raw scans and... it's not as straightforward as I thought it would be. The scans (all A3 in size) vary from about 30MB to almost 180. But I know why...
Let's take these two drum scans first - both of the same Pug drawing:
PUG
400 ppi TIFF
File size: 89.9 MB
Format: LAB/16
Profile: CIELAB D50
PUG
400 ppi TIFF
File size:
30.6 MB
Format:
Grey/8
Profile: Greyscale D50
The second
smaller file is a better, more usable scan, because it's as sharp and detailed as the larger file, and it has correct contrast (white balance was set to register the paper as white). Both are D50, which is greyscale (so, no stored colour data). Both are 400ppi resolution. BUT the first one is a
16-bit scan, and the second is an
8-bit. Hence, the difference in file size. I'll return to that.
I took another, the Old English Sheepdog, which is a big
179 MB TIFF file.
B17 OES.jpg
OES
600 ppi TIFF
File size: 179 MB
Format: RGBa/8
Profile: sRGB IEC61966-2.1
That is a resolution of
600 ppi rather than 400. And it's a
full colour scan - not greyscale.
600ppi is probably overkill. In my experience, 300ppi (that's 'pixels per inch') is sufficient for a clean and sharp print. And, I believe, it's the commercial printing industry's standard resolution.
Greyscale is OK. There is no colour in graphite. Well, actually there is a faint brown tint from the clay, but you don't need that in the scan. On a
domestic flat-bed scanner I always recommend scanning at 300ppi in COLOUR (RGB). Then you can reduce that to greyscale later. That's because RGB collects 32-bits of data per pixel. Greyscale collects 8-bits. So RGB can often capture more of the subtle detail, but once captured, you can remove the unnecessary colour data.
A greyscale file is about 1/3rd the size of an RGB colour file.
Greyscale is a viable choice when using a laser drum scanner. And you don't need a 16-bit scan. 8-bit is perfectly OK.
So, I think the ideal is:
Image format: TIFF (it's lossless - if you copy/'save-as' you don't lose data)
300ppi resolution (minimum but OK)
8-bit greyscale scan
Paper set to be read as white (that's important!)