Ink is fast becoming a thing of the past: even my local book handlers have a range of computer peripherals, GPSs, digital charts, software and interactive CD/DVD ROMs...and I live in the back end of the sticks.
However there will always be a market for books, magazines and stuff to hang on your wall without any power supply!
In the olden days, photo print qaulity was determined by ISO and resulting grain of the image, with even some 200 ASA transparancies being good enough for enlargements of several feet on photographic paper. If you didn't like the grain, then like being in the Louvre, take a step back and be impressed.
Boots the chemist or Jessops aside, there was also a certain directness when dealing with "ink" printers and the whole colour process: I came into advertising at the very end of the era of direct lithographic printing, "analogue" if you like, where each stage of printing had a different print prep or finishing company. Plates were produced one place often to get the best quality to a price, and the proofs, the large negatives of each colour litho process, were kept by us in a most guarded way! You felt a certain tactile and direct connection to what you could hold in your hand when compared to the mouse jockey world of photoshop which came in soon after.
HOW MANY PIXELS DID YOU SAY ??????????????
Today though, what quality can you expect and what should you deliver for home use?
Take my own Olympus DSLR: 10 Megapixel camera
Largest Image = 3648 x 2736 pixels
This is actually 9.8 mpx and is a ratio of 1.33 height to width: four thirds !
large size : fine means best jpeg compression on the display.
If we have a very high quality black and white print at 330dpi then we can utilise all those pixels to give a size in inches thus:
11 x 8 1/4 inches at 330dpi: in other words an A4 side! 210x270mm
We would then want to print this on a 600dpi home or shop printer to get the absolute best tonal range and depth in B/W for a delivered 330 ppi (pixels per inch). Alternatively, if it was a once-in-a-life time photo, you could either get it printed to silver-chemistry ie photographic paper at 1000-2000 dpi or if you wanted to sell it, go to a photo lithographers and get it done on a plate of maybe 660 dpi or higher.
To have an absolutely best qaulity print in colour though, the size would be one quarter this, because each dot on older printers can only have one colour in "dots per inch" so three or four dots are needed to reproduce each pixel to a degree of highly accurate hue (tonal / colour range) and tonal depth (brightness/saturation).
However, printer technology cheats: the high quality 330 dpi - 600 dpi home printer is available to reproduce large PPI quite well to an acceptable quality. The printer driver compiles the pixels into a best colour match for it's hue, saturationand tonal depth and recreates this as points composed of many dots, utilising a best compression and half tone ink saturation to process the image to a best appearance.
The Practice of Relativity
An A4 sheet is 210 by 280 mm, that will say 21cm by 28cm or 8.25 x 11inches by
A HD screen for now, has 1920 x 1080 pixels, so most digital cameras now can fill at least twice that size with an image without any "pixelation" ie a very good image!
A good quality print can be achieved at relatively low dpi, as to be seen at http://www.smugmug.com/help/print-quality. Here an image is printed out to a large size to convince photographers that the eye actually does not percieve more than 80 dpi as poor, quite the opposite. PC screens are 72dpi, while macs used to be at least, 100dpi or lines equivalent. Another reason MACs were better for graphic work.
The image shown, a racing car, lends itself to an easy reproduction though: it has good contrast, sharp details but no very thin lines or patterns, a thrown background and bright colours. It is printed at 80dpi on a large format just to show how good you can get from precieved lower than usual print quality.
So for a colour print you may expect to be able to get a perceptably high quality at 200 PPI priting out at max resolution for the printer 300 dpi or so. This means that :
18.25 x 13.66 inches
When we say high quality in this instance it means for print material seen from a normal reading distance, not under special scrutiny.
For a potrait to be hung on a wall and viewed from a greater distance then a far lower DPI may be acceptable: even 72ppi or normal screen resolution may be practical for printing:
50 x 38 inches @72dpi
Printers use either lithographic plates or screen print by in large : ink jet printing is still not cost effective enough for publishing and laser -toner printers are not there yet either.
Lithographic means the process of chemical etching the colour separations from the original negative : in the old days when I worked with printers, these were best achieved from wide format camera negatives or positive transparencies (slide film) using a series of different filters to create the plate for each colour ink.
Chemicals were used to mask and etch from exposing the plate to light,
and plates for say A4 book printing at 4 sides a plate plus "bleed area" were between £300 and £1000 per set.
The print plates are then loaded up on the press and in use, coated with ink and pressed to the paper which is moved very accurately through the different parts of the print line. Hence the registration is very good as time is taken to ensure problems are eliminated by good preparation or stopping the press asap.
A usual "screen" or lines per inch equated to 330dpi and images in photoshop were handled at that level of ppi, with some leewaywith a "positional" associated to the quark express file such that the printer could use their expertise in preparing : often delivered up to 20% larger than needed to a quality printer image before and during the production of colour separations.
Litho' as it was affectionately called, was at one time too expensive for reproducing ordinary print. Books as late as the 1970s when I was a nipper, often had sections of colour "plates" bound in at convenient points in the book : these were often a pain to refer to from the story or reference as the convenience was only for the printer to sew in the better quality paper such that each insert spanned four pages.
You can still see this today in many biographies in paper back, where images of exploits in the SAS or whatever are collected in the centre or at two points in the book. Paperbacks, like newpapers and most large catalogues are screen printed.
Screen print works by having a mesh screen over a drum with ink being rolled on continuosly and another drum compressing the paper roll onto the print area. The paper like a gigantic toilet roll. Thus it is continuous for huge quantities of thin and therefore cheaper paper than could be used in plate presses.
Originally screen was just in black and white with maybe an extra colour, red most often, for the banner line being used. This is where "half tone" and other screen adjustments came into use to produce reasonable quality black and white photo reproduction by creating a better tonal depth and contrast in a print image than the dpi or Lpi as they call it, would permit. However colour separations came into use in the 1980s: some seem to use RGB for colour areas with a usual black screen being used in both images and text, others CYMK.
The great advantage of screen printing is the huge volume of paper that can be printed in a short time: however it is limited in dpi and also is prone to poor registration: the fuzzy or double images you often see in colour images or graphics. It is very expensive to reset a whole print run if this arises or even to scrap a minutes production, so these are sent out anyway for sale at newsagents etc. Usually you would need to travel to another newsagent chain or even town to get part of the run which was okay!
To save on costs and reduce issues with registration in colour screen printing, many catalogues are printed in three colours : black and two special corporate or style pan tone matched inks. Even some high qaulity art books and magazines use just one colour in addition to black : this can be very dramatic in landscapes with say only the blue or green being there on top of the grey tones.
Today, I would say that all plates on litho and screen is done with laser etching : the image is either purely digital in jpeg format or scanned from a negative or transparency by coloured lasers : the separations are then produced in digital format directly from the latter and by computation from jpegs. The famous "heidelberg" machine for A4 x 4 print plate laser-etching fits nicely in half a squash court with room to walk around it!
Even in 1999 when I was up for moving back to the Ad' industry in Scotland, I went to a printer who still used the grand daddy of them all: type set printing which has it's roots in the wood cut presses used to produce the first printed paper money, and the Lutherin bible in German and English.
The university printers a decade before still used these presses and the prepared litho plates for BW logos, drawing or other images. These lacked any real grey tones!
To cut you data nuts down to size in a little Luddite fashion, the term "upper case" refers to the case containing capital lead letters the type setter would reach into when required in assembling scentences onto the type face for printing!!
The CYMK was industry standard but by the mid nineties all printers I knew could have atleast a fith colour or technical process, like a UV spot filter or spot varnish. K was used for black : to do with not being confused with
"Blue" which was used before cyan was the colour chosen.
The trouble with CYMK is that it does not produce all colours equally well, eg orange, and where printers used to mix specific inks to match hues in a book say on birds by James Bond with colour plates in the 1950s, that art is no longer seen as cost effective. Blue skies often have a purpely appearance with notable red dots and this is due to the clash between the cyan and the magenta fighting to make a blue which is near cyan but not near enough.
Orange is never well reproduced as it is a mix of yellow and red: magenta is not red enough and some cyan comes in the litho process or digital separation: thus orange on any CYMK standard pallette if you like, is a mucky brownish orange.
Correspondingly, Orange telecom in the UK were the first company I heard of who stipulated a fifth colour process with of course, the proper corporate pan tone orange for their block logo and fonts.
The extra processes, colour or treatment, use the same basic component parts of the four colour process; a machine unit which very accurately places the paper from the last print onto the next plate. Thus software skills, investment and pure physical factory area are the external limiting factors, while there are limits to how much ink a paper will take.
Even in CYMK, when printing black areas with photos supposed to be frameless, mysterious "chinese window frames" would appear where a positional frame around the image became "super saturated" and shiny with layers or ink.
Many of the top printers for corporate material went over to seven colour process print lines for litho printing, which may seem a bit like "being the last to make buggy whips: darn good buggy whips" while everyone goes new media.
On the topic of new media, jpeg is in RGB which suits of course LCD monitors very well. However now four colour TV Flat screens are available with a yellow which gives a more pleasing and realistic colour than RGB. Although this may take some time to come to the general market for computers, the technical challenge of "re-separating" an RGB signal to a fourth colour is now practical for better reproduction!
Technically RGB in an LED screen should be perfect colour reproduction as the transmitted, addative colours are bright enough to give hue, saturation and BW tonal depth is better due to the "black ness" of the LEDs which are not transmitting.
A pixel contains a given value for both the hue and the tonal depth: the shade if you like. The LAB set up is actually far better at handling images for print and absolute quality (even when considering CYMK as final out put) but because RGB is the standard for monitors then this is the prefered handling.
I would expect , or wishfully think, a move over to image production using the LAB system where the BW is it's own separation: red green and blue yellow are the other two separations so the fourth colour would be a yellow, making probably for better judgements from eye to screen in what is a good colour adjustment in the "ring" of images shown in most software packages.
I would look to Mr. Jobs' job when that frickin iPaddy makes the stock fall and they move back to their home land of graphic arts.
The requirement to produce a better quality image nearing the ppi x 4 required is driven in part by the content of the image.
Obviously if the subject of the image contains a lot of fine detail or pattern which the eye is lead to, then a high dpi will produce the best results.
Conversely, lack of detail and contrast can require experimentation for best print outs.
Both high light and low light images have subtle tonal differences in BW alone, and any noise from the CYMK compression / conversion detracts from the qaulity: Also the tonal depth will need to be enhanced due to this subtle changes over areas of the picture such that they don't appear "posterised" with harder changes between areas appearing as bands or lines not present in the original.
Hence you need to have four colours per pixel to make an acceptable print quality and thus on a 330 dpi printer you need to divide your megapixel size by 1320 to get how many inches would be absolute best.
Best Fit ; ppi: dpi and image scaling
Practically it would be quicker to use some trial and error, by first printing out a small scale size at 330dpi in colour, or lower quality like 100dpi to see the areas which may be problematic in percieved image qaulity.
Then take a crop of these potentially troublesome areas and vary the size of the image output, writing a text comment with their details so you can keep track of them after printing : view then from a distance and determine which size is acceptable. Calculate out your total size achievable: it will probably be bigger than your printer's width and height!
A picture with less tonal depth and more primary colour composition, more contrast and stronger colours in other words, would maybe be a direct conversion to 330 ppi to dpi or lower upon some scrutiny.
At this stage it would be far easier to move away from using ppi and the whole pixel thing, and use PS's, or light room or Corel's etc etc, image scaling function which gives you dpi and actual inches size or metric E-Qs.
Notes on sizes
YSF YF YN YB
3200 x 2400
2560 x 1920 XSF XF XN XB
1600 x 1200
1280 x 960
WSF WF WN WB
1024 x 768
prints and use
on a web site
640 x 480