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does anyone know what the standards are for print download? from what i can gather, .tiff is the best format to store my archived copies, but will be waaaay to big to offer as downloads. it seems that most print outlets (newspapers and magazines) are accepting hi res jpgs.
is 300dpi the standard? do i need to think about pixels? or should i be saving in inches?
i've just started researching this and don't want my photographer to go ahead and start scanning in 20,000 images, only to have to re-do them all at a later stage!
very new at this side of things, would be very grateful for any help.
I would recommend that you give Photoimpact from Ulead a shot. It is an excellent program! If you do a search in Google you will find a number of forums that discuss this great graphics program.
Now, the filesize of a picture is dependent on
1) the relation between final size and original size
2) the dpi (dots per inch) or ppc (points per centimeter) of the final product
3) the number of lines per inch/cm (lpi/lpc) used to represent a picture
Now, as an exercise for the readers, try using a magnifying glass on
1) your daily newspaper
2) a normal magazine
3) a high-quality printed art-magazine
4) an advertizing poster / billboard
5) your computer screen
5) your tv screen
notice first of all the difference between the printed medium and the screen: the screen uses three pixels to represent all colours and achieves this by varying the intensity in each of the three pixels. The printed medium uses pixels of varying sizes that fools the eye into seeing continuos colours.
Now, I'll pass over most of the nitty-gritty details of the printing process and focus on the scanning side of things.
Each of the examples in example 1-4 uses different lpi/lpc. The dpi/ppc isn't of much interest to us. The value of the lpc goes from about 4 for the billboard poster up to about 144 for the art magazine and a normal magazine is at about 48 lpc. So lets do some calculations:
A4 is 210 x 297 mm ; a 35 mm negative is 24 x 36 mm : magnification : ~8.5
48 lpc means we need 21x48 = 1008 pixels and 30x48 = 1440 pixels
correction/quality factor : either the square root of 2 or the fourth root of two.
Now, of course if you only want to use a little part of the negative and blow this detail up, you magnification factor increases correspondingly. And it dcecreases if you don't want to do an A4 magazine page.
Taking these into account we get:
memory needs : 1440x1008x1.41x24bits = ~6MB
scanning density : 48x1.41x8.5 = ~600ppc or 1500dpi
In the memory needs I've calculated using 3x8 = 24 bit scanning. If your scanner can do 30bit or 48bit scanning your memory needs of course increases.
It's left as an exercise for the reader to do the calculations for other examples - now you at least know how to do them and the factors involved :-)
And I do know that you'll be surprices about some of these numbers.
Now, you are asking : where does the printing dpi enter into the picture?
The answer is, that you take the printing dpi and divide by the lpi, square this number and get the number of colours you are able to represent per colour channel.
Example 600dpi printer at 48lpc/120lpi = 5 which means that you'll only be able to represent 25^3 = 15,625 colours which is a far cry from 16M!
Now, going the other way : how many lines can you get if you want 16M colours in your output?
Answer: 16M is 256^3 ; the square root of 256 is 16 ; dividing 600 by 16 and you get 37,5lpi/15lpc which is half of the quality you typically get in a newspaper!
Now, for processing pictures the prepress people really like to work with loss-less compression, so for the highest quality go for tiff.
[edited by: BjarneDM at 10:40 am (utc) on Mar. 5, 2003]
BjarneDM i really appreciate your mail - it's really getting into nitty gritty. but frankly i got lost half way through and wondered if you would do some mathematics for me as this is VERY important for me at this stage.
if i have a 35mm slide and i want my highest res .TIFF file to be able to be used for magazine front cover quality (anything else i can scan in as a special job) say 8 x 10 inches, what would my file output be?
the format i want is TIFF and i know the file size will be huge (i can compress), but what else should i ask the scanning bureau to do? should i ask for a specific size in inches and dpi? or inches and lpi?
this is the one area i just can't figure out...some people say dpi, some say ppi and some say lpi.
your recommendation?
You will have to send them to a DECENT bureau, that means not one of those ones that knock out scans in a hour for a tiny amount of money but one with someone who actually understands about colour space and resolution. The next problem is that we always scanned to the size we needed the image. Obviously with your downloads you won't be. I think here you have to think about what you need to do. Honestly I don't feel the idea is that great. When I was studio manager I would rather see a site where you could download some jpegs that would work in a visual and if approved we could buy the 5x4 and get that scanned by someone we knew would give us a good result and to the right size.
there are also big issues with tracking who has which slide and their return. my guy is not big on administration and has lost thousands of slides over the years!
most customers are happy using my client's hi res jpgs which he scans in himself and emails to them (he has a very unique portfolio so publications put up with it for now) but frankly his scanning technique is so appalling that i want to get something far more flexible that can cover 80% of internet orders abroad. for the rest i am happy to have custom scans done....
i guess the question comes back to the best format i could have done for a portfolio of 40,000 35mm scans bearing in mind cost, quality and time. i do think a bureau will be better at the moment. just really not sure what to ask them to do!
so, dpi = 2.5 x ppc ; lpi = 2.5 x lpc. Where it gets confusing is when the scanning and printing people are mixing per inches and per centimeter in the same sentence
your memory needs are also dependent on
1) the number of lines (read: quality) that the printers want to reproduce,
2) the number of bits per pixel that the scanning people can give you
as to the scanning people a good recommandation is just to ask them to deliver in the highest resolution and the greatest bit-depth they can give you.
try reading my post again :-) there shouldn't be any units or numbers that aren't explained (except that 8b (bits) = 1B (Byte) - which I used to calculate memory needs); and try to do the math by yourself - it really isn't that hard, but the number of variables makes it hard to give any specific calculation beyond the general algorithm.
The nitty-gritty I left out are:
RGB to CMYK converting - pointspreading in the printing process - rasterisation angles - rasterisation point type (square, circle, ellipsis) - gammacorrection - etc etc :-D
I work for Newsquest Cheshire, responsible for local papers and publications like the Warrington, Congleton, Northwich, Newton Guardians and some supplement magazines such as Twos Company.
We use minimum 300 dpi for our high quality magazines
we use minimum 150 dpi for our newspaper images
we use 72 dpi for our web graphics.
Until recently we used eps files, however nowadays we have started to use high res jpg's and pdf files.
Package wise, we use Adobe Illustrator and Photoshop, and that allows us to do everything we need to!
I would rather see a site where you could download some jpegs that would work in a visual and if approved we could buy the 5x4 and get that scanned by someone we knew
Jane, I think he means he'd rather get a preview JPEG and then get a photographic print of the image... not sending out your original slides. Prints might be a very good sales option to offer on the website, as a tiered pricing structure:
As far as downloads go, it's probably easier just to invest in a (couple of) CD burner(s) and overnight/second-day-air CDR's with the desired images on them. A low-res JPG can be used, as they say, FPO (for position only), to do layout prior to the arrival of the CD...
And any customer who absolutely, positively needs that file TODAY should still be able to download it... For around a 50% extra fee. :)
