Chapter 6- Digital Printing of Photo-realistic Images

Question 1

Ink Jet Printing: The first desk top photo-realistic printers were the Stylus Photo range of printers that worked via their propriety piezo-electric method of ink delivery. What is this?

Answer 1

Small crystals present in the nozzles of the print head are subjected to an electric current which enables them to vibrate. This action forces the ejection of an ink droplet from the end of each nozzle onto the ink-receivable layer of the paper substrate, while more ink is drawn from the ink cartridge

Question 2

Ink Jet Printing: What did the early Epson Stylus Photo printers use as a colour reproduction principle? additive or subtractive?

Answer 2

Subtractive: Cyan, yellow and magenta. The next models had six colours, including light magenta and light cyan to enable better colour rendition of skin tone

Question 3

Ink Jet Printing: Why were these Stylus Photo printers producing images that were susceptible when exposed to light and moisture?

Answer 3

They used dye-based inks- these are not as popular as pigment-based dyes but have a larger colour gamut and the ability to print onto high gloss ink-receiving layers i.e swellable polymer IRL’s, enabling the colours to appear more brightly

Question 4

Ink Jet Printing: What colours do the dye-based Epson Stylus Photo printers use?

Answer 4

Cyan, Light Cyan, Magenta, Light Magenta, Yellow and Black

Question 5

Ink Jet Printing: What colours do the pigment-based Epson Stylus printers use?

Answer 5

Cyan, Yellow, Vivid Magenta, Photo Black, Matte Black, Light Black, Light Cyan, Light Light Black and Vivid Light Magenta- Others may include green, blue, orange and violet to extend colour gamut

Question 6

Ink Jet Printing: Why is black ink used together with matte black ink in pigment-based printers? Why are the additional light black and light light black added?

Answer 6

To alleviate an effect called ‘bronzing’ (this is also counteracted by the gloss optimiser cartridge). The additional two blacks are added to try and match the tonal range of conventional silver halide monochrome printing papers

Question 7

Ink Jet Printing: In competition to the piezo technology method of ink printing, there is the thermal/bubble jet equivalent (HP and Canon). How do these systems work?

Answer 7

These systems have a tiny resistor (heating element) behind each nozzle and when a current is applied, the temperature increases rapidly to 300/400 degrees C and this causes a bubble of vapour to form in the ink. This results in ejection of an ink droplet from the end of each nozzle. This creates a vacuum in the nozzle which pulls through new ink to replace the ejected ink

Question 8

Ink Jet Printing: Comparing pigment and dyes, answer appropriately what traits they have in reference to the following:

Brilliance
Gamut
Colour shift
Wicking on paper
Penetration
Metameric problems
Differential gloss

Answer 8

Pigments-

• Lesser
• Smaller
• Little as these are particles
• Little to none
• They sit on the surface and do not penetrate into the ink receiving layer
• Possible both differential gloss and coloured bronzing common on glossy media

Dyes

• Greater
• Larger
• Some colour shift after printing
• Yes
• Penetration into ink receivable layer
• Unusual
• Differential gloss on glossy polymer media is possible

Question 9

Dedicated Photo-Quality Papers: Why does dye wick on normal paper?

Answer 9

Because it is in a solvent and there is no ink-receivable layer on the paper to hold the position of the ink in place

Question 10

Dedicated Photo-Quality Papers: Ink-receivable layers tend to fit into two categories; swellable polymer and pigmented microporous/nanoporous. What are swellable polymers and what are they made from?

Answer 10

Swellable polymer IRL’s consist of a network of long polymers that swell as they absorb the solvent component of aqueous ink. Typical ones used include gelatin, polyvinyl alcohol, polyvinylpyrrolidone, methyl cellulose, carboxy methyl cellulose and polyacrylic acid

Question 11

Dedicated Photo-Quality Papers: How do swellable polymers work?

Answer 11

The ink penetrates the swollen polymer layer and the dye colorants are fixed in the lower mordant layer, which typically contains a cationic mordant or cyclodextrin. A lower mop-up layer absorbs the solvent components of the ink. Due to the dye colorants migrating through the polymer layer and become fixed in the mordant layer, this gaurantees maximum colour brightness and affords a level of protection for the image with respect to light fastness. Once the solvents have been absorbed/evaporated, the swellable polymer returns to its original state and seals the various colorants

Question 12

Dedicated Photo-Quality Papers: Due to the swellable polymer IRL’s being glossy, matting agents are required if reduced gloss is wanted. What agents are normally used for this and what other job do they do?

Answer 12

Silica and synthetic resin beads are used. These serve as a dual purpose, as they tend to protrude over the coating, thus allowing a thin layer of air between the paper sheets to prevent them sticking together when many are printed

Question 13

Dedicated Photo-Quality Papers: What are the main disadvantages of swellable polymer IRL’s?

Answer 13

They are slower to dry than pigmented microporoud/nanoporous types and remain more sensitive to environmental humidity changes but they do give better protection against light and gases by means of fixation to the mordant layer. Another disadvantage is that these are not compatible with pigment-based inks as the pigment would be deposited on the surface and therefore would be susceptible to abrasion

Question 14

Dedicated Photo-Quality Papers: What are microporous/ nanoporous pigmented IRLs?

Answer 14

Single layers with microscopic particles of amorphous silica (silicon dioxide) and/or alumina (aluminium oxide), dispersed within a synthetic binder such as polyvinyl alcohol

Question 15

Dedicated Photo-Quality Papers: How do porous pigmented IRLs work once the ink has been dropped onto it?

Answer 15

Solvent component is immediately absorbed by capillary action into the porous particles. Dye-based inks will absorb to a certain degree into the porous base, with anionic dyes becoming bound to the cationic alumina particle surface or the modified cationic surface of silica particles. This reduces mobility of the dye colorants in high humidity and also if liquid contact occurs

Question 16

Dedicated Photo-Quality Papers: What is the key advantage to pigmented microporoud and nanoporous IRLs? What are the disadvantages?

Answer 16

The media immediately appears dry when touched- it is important to know that the total evaporation of the solvent can take some time-around 24-48 hours. Another disadvantage is that this type of IRL is less sensitive to humidity changes bur offers little protection against gases which will degrade the dyes. This IRL is ideal for pigment-based dyes

Question 17

Colour Management of Photo-Realistic A4/A3 Prints: To ensure the original colour of the image is reproduced correctly, it is important that the PC and printer are calibrated and profiled. What is meant by needing to be in a situation of ‘WYSIWYG’?

Answer 17

What you see is what you get- so that the image on the screen is what will be seen when it is printed. When you calibrate your moniter, you are matching the monitors colour and contrast to an international standard

Question 18

Colour Management of Photo-Realistic A4/A3 Prints: Which calibration and profiling system is good for wedding, portrait and event photographers?

Answer 18

X-Rite ColorMunki Photo instrument

Question 19

Colour Management of Photo-Realistic A4/A3 Prints: Moniter Profiling: Using the ColorMunki software, what are the stages of calibration and profiling of the PC monitor?

Answer 19

1) Ensure moniter has been on for 30 minutes prior to this
2) Disable energy saving settings to prevnet monitor being turned off
3) Check the screen for uniformity
4) Set screen resolution to vnormal working setting and the Bit-depth to maximum
5) Disable Adobe Gamma (or any other calibration system present) so that there is no conflict with the software
6) Ensure the monitor is the brightest light source in vision to increase contrast and therefore allow the operator to see detail in image (purpose designed monitor hood is helpful)
7) Adjustment of white point, gamma and luminance is important to achieve a match with the printer (2.2 for for gamma and 100-120 cd/m2 is good for luminance)

Question 20

Colour Management of Photo-Realistic A4/A3 Prints: Moniter Profiling: What do the colorimeter/spectrophotometer do?

Answer 20

They provide measurements for the creation of ICC profile for the screen display (Colorimeter not as able as spectrophotometer). This is a colour map of how the monitor displays different colour values and allows software such as Adobe Photoshop to ensure the accurate rendition of all images. (ICC profile= data and text description of device set up basically)

Question 21

Colour Management of Photo-Realistic A4/A3 Prints: Colour Printer Profiling: The next part of the process is to ensure the printer is calibrated correctly. What sort of devices (additive or subtractive) are all ink jet printers’ drivers? What about thermal dye transfer printers?

Answer 21

RGB- The driver takes in RGB data and then converts to a pattern of CMYK dots for the printer to output
Thermal dye transfer printers are also treated as RGB printers even though they use CMY transfer ribbons

Question 22

Colour Management of Photo-Realistic A4/A3 Prints: Colour Printer Profiling: Do many photo-realistic printers have their own calibration and profiling system built in? What should you do if you are using third-party paper and inks?

Answer 22

Yes, when using OEM (original equipment manufacturer) paper and ink, the results may be suitable for amateur photographers, the settings of how much ink needs to be deposited are already programmed. However if using different inks or papers, it is important to create a specific profile

Question 23

Colour Management of Photo-Realistic A4/A3 Prints: Colour Printer Profiling: If a close match is not found when using a third-party paper, what can this lead to?

Answer 23

Ink puddling (excessive wet ink)
Ink spreading and feathering
Poorly defined lines or type
Pattern development in dark colour areas of print

It is advised to change the paper in this case as even creation of an ICC won’t solve these issues

Question 24

Colour Management of Photo-Realistic A4/A3 Prints: Colour Printer Profiling: With respect to profiling, there is usually the choice of outputting between what range of colour patched for measurement purposes?

Answer 24

300-1000. Exception being X-Rite Colour Munki which only outputs 100 colours (2 sets of 50). The colorimeter is scanned over a 50 patch printed test chart and the software records the colour behaviour of the printer/ photo-quality combination. The software then generate a second set of 50 patches which are then printed and scanned, generation a profile for the printer/substrate combination

Question 25

Colour Management of Photo-Realistic A4/A3 Prints: Colour Printer Profiling: Why may the few colour patches of the X-Rite Colour Munki be considered advantageous and why might it be disadvantageous?

Answer 25

Fewer patches can make a more accurate profile, providing the printer is printing evenly across the tonal range for each individual colour. However, if this printer is not linear then more patches will be required for a more accurate profile.

Question 26

Colour Management of Photo-Realistic A4/A3 Prints: Colour Printer Profiling: How long should inkjet paper prints be left before measuring the colours?

Answer 26

At least an hour to allow the print to stabilise

Question 27

Colour Management of Photo-Realistic A4/A3 Prints: Colour Printer Profiling: Where is it best to save your newly created profile?

Answer 27

In Adobe Photoshop rather than the printer drive or operating system

Question 28

Thermal Dye Transfer Printing: This is the principle competitior to inkjet printing, especially to event photographers who want to supply images during the actual engagement. What is this process often referred to as?

Answer 28

D2T2 or Dye Diffusion Thermal Transfer

Question 29

Thermal Dye Transfer Printing: What is the main advantage of this over inkjet printing?

Answer 29

Produces continuous tone image as opposed to inidividual ink droplets so the image looks more like a conventional silver halide image- no pixelation, providing the image file is at the required resolution i.e 300 dpi

Question 30

Thermal Dye Transfer Printing: How does this process work?

Answer 30

Using subtractive colours, fuses the dyes into the thin receptor surface coating present on the specificallt designed media. The quantity of dye transferred from the colour donor ribbon, via thermal array, is directly proportional to the level of heat applied, thereby ensuring continuous tonal images. The individual pixels fuse together on the substrate in a seamless manner. As the final image is not fully fixed (only semi-bound within the receptor coating by chelating compounds that metalise the dyes), all current printers apply a protective waxy polymeric overcoat to help protect the image from UV component of light and potential migration of dye into materials interacting (e.g storage plastic wallet)

Question 31

Thermal Dye Transfer Printing: Describe the structure of a thermal dye transfer print (the layers seen through a cross-section).

Answer 31

Wax topcoat
IRL where the dye sits
White base coat
Synthetic paper
PE with TiO2
Paper
PE
PET
Anticurl layer

Question 32

Thermal Dye Transfer Printing: Fuji Autochrome Printer: This is a further thermal transfer system available; the paper substrate uses an exclusive heat-sensitive microcapsule system with new diazo compound and coupler technology held in three colour layers. Descrive the sequence of events that take place for the printing process.

Answer 32

1) First cycle- yellow dye layer developed first using low thermal energy. Yellow image then fixed by a 420 nm UV lamp (decomposes undeveloped colour elements)
2) Second cycle- magenta layer is developed using mid-range thermal energy and then fixed using 354 nm UV lamp
3) Third cycle- cyan layer is developed using high range thermal energy

This is similar to normal film but no chemicals are involved, just UV

Question 33

Electrophotography: This form of printing is based on light and electrostatic charge. The process itself is centred around a light-sensitive photoreceptor drum. What are the 6 key stages?

Answer 33

1) The photoreceptor drum receives a uniform electrostatic charge
2) The laser then writes image info onto the photoconductor drum and at the same time the electrostatic charge is dissipated
3) This results in a latent image being formed in the uncharged image and charged non-image areas of the photoconductor drum
4) Latent image then made visible by means of toner application which is repelled to the uncharged image areas due to the particles having the same charge as the non image areas
5) The toner-filled image areas are then transferred to the oppositely charged paper surface
6) The toner is fused to the paper surface as it passes through two pressure rollers which are heated

Question 34

Print Systems incorporating Silver Halide Technology: What are the 4 key criteria in order for a printing system to be deemed successful?

Answer 34

Photo-realistic appearance and feel (this is very well done by silver halide printers)
Print output speed
Image stability
Cost factors

Question 35

Print Systems incorporating Silver Halide Technology: Fuji Photography Imaging System (general silver halide printer): What is this system based on (the methods) and what sort of photography is it used for?

Answer 35

Photothermography and dye diffusion principles
It is a low volume (not mass production) printing system and is used for studio photography, aerial, retail stores and proofing applications

Question 36

Print Systems incorporating Silver Halide Technology: Fuji Photography Imaging System: Describe the photothermographic transfer process.

Answer 36

Exposure of emulsion layers to light containing the three colours

Donor paper moistened by water to active a base generating chemistry

Donor sheet then sandwiched with receiving layer and thermally processed at 80-90 degrees C for 30 seconds, causing latent image to develop

DRR groups associated with the silver halide crystals are activated by the heat and alkaline environment, causing reduction of silver ions to silver, thereby releasing the dyes.

Small volume of water causes the cyan, yellow and magenta dyes to diffuse into the receptor media where the dyes are anchored to mordants present within receiving media.

Final stage involves peeling apart the donor sheet and receiving media which is then ejected from printer as the finished print and donor sheet shaved for silver recovery

Question 37

Print Systems incorporating Silver Halide Technology: Digital Exposure to Photographic Processes: This exploits advantages of digital imaging whilst using light-sensitive silver halide based photographic materials such as paper and film so essentially the result is an image identical to its analogue equivalent but it has been generated from a digital file. What sort of colour reproduction method does it use?

Answer 37

This uses the additive colours- there is a red, blue and green light that exposes the digital file to photographic material

Question 38

Print Systems incorporating Silver Halide Technology: Digital Exposure to Photographic Processes:
What three common devices are used to produce large scale photographic prints from digital files?

Answer 38

Durst Lambda Printer, Oce LightJet Printer and LumeJet Printer

Question 39

Print Systems incorporating Silver Halide Technology: Digital Exposure to Photographic Processes: Using the Durst Lambda Printer, what sort of lasers are used and what format photographs does it produce?

Answer 39

Constant intensity RGB lasers are utilised
Each beam passes through a modulator device which has capability of altering input brightness to one of 256 levels that correspond to the individual RGB values of each pixel of a standard 24-bit digital file (v. high quality for v. large format). The three beams then converge into one using lenses when exposing the roll substrate material. Very good for banners as there is no limit on width of photo

Question 40

Print Systems incorporating Silver Halide Technology: Digital Exposure to Photographic Processes: How does the Oce Light Jet Printer work?

Answer 40

A spinning mirror traversing the centre of axis of the drum exposes the photographic paper dot by dot and line by line.

Question 41

Print Systems incorporating Silver Halide Technology: Digital Exposure to Photographic Processes: How does the LumeJet Printer work?

Answer 41

Uses multiple-parallel independent beams of photons
of various wavelengths and spot sizes to generate the image
The multi-LED exposure head is approximately the size of an inkjet cartridge
Works in a similar fashion to inkjet printing but sprays light onto photo-sensitive silver halide media instead of ink onto ink receivable coated papers
As with inkjet, the multi-LED exposure head can move and traverse the media (for large format printing), or be mounted in a static bar configuration while the media passes underneath (ideal for highspeed printing). In the moving head version,light (photons) from an LED array is directed through a custom designed fibre-optic taper and focused onto the media via a 1:1 relay lens

Question 42

Print Systems incorporating Silver Halide Technology: Digital Exposure to Photographic Processes: Why id the LumeJet Printer so successful in the industry?

Answer 42

It has the ability to produce pantone colours much better than others

Question 43

Image Stability and Print Durability: Are dyes or pigments more stable?

Answer 43

Pigments have better stability

Question 44

Image Stability and Print Durability: Visible Light and UV Radiation: What sort of printers showed poor image stability in early days of development when the image was exposed to sunlight?

Answer 44

Ink jet photo-quality printers

Question 45

Image Stability and Print Durability: Visible Light and UV Radiation: What are the three main mechanisms associated with light and UV radiation that can affect image stability?

Answer 45

Photo-oxidation, Photo-reduction and UV-related bond cleavage. These cause the dye/pigment to fade and rarely occur due to light alone and require the presence of oxygen and water. The actual fade process is by reactions that break colourants down into different components that have different absorptions (dyes) or reflection (pigments) compared to original ones.

Question 46

Image Stability and Print Durability: Visible Light and UV Radiation: Why will dyes fade faster than pigments?

Answer 46

A pigment is present on IRL as crystalline particulate so only a tiny percentage of the molecule that make up particles is present on the actual surface. This means that if the molecules on the surface fade then the bulk of the particle will still have colour. Dyes exist on the IRL as either single molecules or small aggregates meaning they are more susceptible to fading

Question 47

Image Stability and Print Durability: Visible Light and UV Radiation: What is catalytic fading?

Answer 47

A synergistic effect associated with dye-based ink jet inks and is cause by mixed colourants- this tends to occur in darker areas where more ink is present

Question 48

Image Stability and Print Durability: Temperature and Relative Humidity: What is ‘dark fading’?

Answer 48

Deterioration of images stored in the dark by temperature and humidity. It causes colour fading, colour balance shift (darker colours may shift into lighter colours) and yellow staining

Question 49

Image Stability and Print Durability: Temperature and Relative Humidity: What does high humidity alone cause?

Answer 49

Migrating of magenta ink jet dyes and growth of mould and bacteria especially on gelatin based media

Question 50

Image Stability and Print Durability: Temperature and Relative Humidity: What does high temperature alone cause?

Answer 50

Drying out of prints causing mechanical stress between the layers of the material such as ink jet and thermal dye transfer prints

Question 51

Image Stability and Print Durability: Water: Why are dye-based ink jet images more susceptible to damage by water than pigment based?

Answer 51

Because dyes are water soluble

Question 52

Image Stability and Print Durability: Air Pollutants: What are the consequences of air pollutants on images? What air pollutants can affect image stability?

Answer 52

Cause them to change to an orange hue when using dye-based ink set on microporous media. This is due to the fact that there was chemical degradation of the organic colourants and of the polymeric binders found in digital prints

Nitrogen oxides
Peroxides
Sulphur oxides
Hydrogen sulphides

Question 53

Image Permanence Standards for Digital Prints: What does the ISO standard tell you about film and paper images? Is there an equivalent for digital prints?

Answer 53

Method for determining the long-term dark storage stability of colour images and the colour stability of such images when exposed to certain lights at certain temp. and humidity

There is no such thing for digital images

Question 54

Image Permanence Standards for Digital Prints: Why is there no ISO standard like method for digital prints?

Answer 54

Due to disagreements between Wilhelm and Kodak companies on test parameters for light and dark stability methods. This has led to different ‘years-of-life’ predictions for a range of inks/ media. The Japanese now have their own standard for digital prints and there is hope that soon we will too due to an improving relationship between the two companies

Question 55

Image Permanence Standards for Digital Prints: What have the range of test methods being used at the moment focused on extending?

Answer 55

Test target to encompass skin tone colours by ink jet printers

Question 56

Image Permanence Standards for Digital Prints: What is the current situation involving stability standards as of 2011?

Answer 56

A test of print water fastness testing has been introduced
A test on humidity fastness will be published soon
Predictive test on thermal stability and pollution will be published soon
A standard for light seems far away