FADE & LINE QUALITY TESTING

Fade testing

A fade testing standard remains a contentious issue with no immediate resolution in sight. Henry Wilhelm, secretary of the relevant ISO technical committee wrote, in a recently published report, 'In several significant aspects the new ISO 18909 is viewed by this author as a further, significant, weakening of the previous, already weak, standards.' In another part, Wilhelm takes Kodak to task for claiming fade resistance for its Ultima paper using a methodology which inflates the anticipated life between 4- and 8-fold – small wonder that the consumer is confused and it seems likely that ISO 18909 is not going to clear the air. The conclusion may be drawn that the only way to maximise fade

„` Use only pigmented ink from a reputable source.
„` Use only paper with a microporous coating.
„` Use acid-free papers.
„` Use OBA-free papers.
„`Use a postproduction spray or brushed coating, if you can.
„` Treat the prints with care; mount behind glass, out of direct sunshine.

Humidity Testing

This is an area where a lot more data has surfaced, not all of it welcome. We have for some time had a test-sample series waiting to be written up. Prepared by Martin Sellars, they are a horrifying collection of faded, discoloured and damaged dye ink-jet prints which have been subjected to little more than the passage of time in moderately damp conditions. Exposure was to indirect winter sunlight, behind glass, for 81 days between mid-November and early February. The prints were subjected to the humidity but half covered against light exposure, all were taped in the same window. The bleeding of the dark colours into the lighter ones – so-called lateral bleed – is as much as 1mm. We have been beaten to publication by Wilhelm Research which published in 2003 and 2005, but its data looks to be a close mimic of what we have observed. Wilhelm has spent its time devising a methodology for quantifying lateral diffusion of colourants under humid conditions, by using a simple spectrographic analysis before and after exposure to generate a Line Quality Retention value. Its data show that pigmented inks and microporous coatings are good and that dye pigments and swellable polymer coatings are very poor. The downside is that Wilhelm has also published data showing that ink fade due to the catalytic effect of ozone is worse with microporous ink than with swellable polymer! Again this points to a microporous/pigment ink solution, possibly with the addition of an applied coating to protect the finished print.

Grayscale card

The images on this page and the table on the previous page show some of our data. In practical terms we observe that our model was wearing silver earrings when photographed but that they turned to a rich gold colour on exposure, when imaged with dye ink onto a swellable polymer substrate. In some instances, the loss of density due to light exposure amounted to between 30 and 36 Lab Delta E points. It was not all bad news though. RA14, Kodak Dye Sub (its 8500 model), Epson Ultrachrome Ink and Epson Enhanced Matte paper (a Microporous media) fared very well. Epson Dye ink was better than third-party dye ink. Testing of this type is very complex with multiple, interactive variables. However for long-term stability the message remains as listed on the opening page, except that you can drop the Kodak 8500 and RA 14 into the good mix! Epson comes out well from all this, their dye ink was better than third-party and the hybrid, pigment/dye, UltraChrome ink set fared well.

Fade 3

ABOVE: This is the test image used by Martin Sellars (original below). The exposed sample, shown left, exhibits gross posterisation and loss of density on the left, which was exposed to daylight, and colourant migration on the right, which was shielded from light, but under the same humidity conditions. This is a dye-ink/gloss paper combination. The enlarged segment of the test, shown below, illustrates the degradation due to lateral colourant diffusion as evidenced by the change in the colour of the earring and the bleed at the edges of the print. The areas marked out in yellow show the zones referred to in the table on the opposite page.

Yellow Stain Formation

Again we must defer to Wilhelm for specific data, noting that we too have observed similar, if un-quantified effects. If a print is left exposed to light, perhaps with another print on top of it for any length of time, the chances are that a tell-tale mark will be left behind. We have observed this on Pictography prints and, in particlular with fans of ink-jet paper swatches, left about in the office. Thus, yellow staining is the appearance of a light yellow tinge to the base white of a print, infecting the highlights and spectral reflections in an image. It is not generally in the same league as the previous two problems discussed here. However we have it on record of one bride bringing back her album because she had detected the appearance of a line under the matte of an album between the exposed and unexposed portions. We are unsure if the change was due to air exposure away from the matte or acid exposure under the matte, loss of ink density or a combination of all three. However the album was returned so beware!

Fade 5 One of the bad actors in this is the optical brightener added to a paper media to create a brighter base and more 'bite' in the image. Optical brighteners (OBAs) work by absorbing light at longer wavelengths and emitting light of lower (more blue) wavelength, by a process known as fluorescence. The presence of OBAs is detected most easily by viewing the paper in 'cold' light, of the type used in discothèques. In practice it produces whites that are 'whiter than white' (to quote the Persil advertisement). The problems start when the OBAs start to break down under the action of ultraviolet light, when the underlying yellow of the paper base starts to show through. This is even more visible if the image is partly obscured during the exposure to light – this can occur if prints are left out in an untidy stack (never we hear you cry!).

The higher life expectancy of pigment inks has taken the outlook period beyond that of traditional silver halide prints and yellow staining now looms as a life-limiting factor of prints stored in nominally dark conditions (eg a wedding album).

The variability and complexity of the ink-jet substrate has muddied the waters yet further. Initial data from Wilhelm is reasonably encouraging but the user should beware of OBAs, non-acid-free papers, and the use of unbuffered, or poor quality, backing boards. As ever, storing the family archive in an old shoe box reeking of acid is a sure way of eliminating a good chunk of the family from your visual heritage! The measurement of yellow staining is further complicated by the fact that the yellow stain bleaches rapidly if the print is exposed to daylight.

Fade 6 And now for the good stuff!

You could be forgiven for thinking that things were in a bit of a mess from what we have talked about so far. However it is not our intention to cast a gloomy cloud over ink-jet, in-house printing; things are relatively bright, especially for the likes of Epson, which seems to have cornered the market for making good stuff. If you take gamut volume as an example, this has been progressively pushed upwards with the high spots being achieved by The Epson R1800 and the Epson K3 ink sets. With its additional inks in red and blue, the R1800 got the gamut volume up to 98.5% of the sRGB gamut. This is not to say that they are the same all over just the same total volume. There is therefore headroom for the next generation of inks to bring in additional colours to expand the gamut yet further. Currently the yellows, some reds, the cyans and the cyan greens are outside the sRGB gamut (ie better than) but the blues and magentas have some space that they can move into. The blues remain an anomaly – always the least accurate colormetrically, but the eye is very accommodating in that part of the spectrum and does not notice any deficiencies. Providing the blue does not drift towards magenta (as it can easily) any improvements are likely to help the copy-line writers but not markedly affect the visual impression given by a print. Sorting out the blacks so that the depth of both art papers and glossies are the same, offers scope for improvement and Epson is some way along the path with their micro-encapsulation technology and hybrid pigment systems – don’t imagine they won’t keep tempting us with yet further goodies in the future!

On the light fastness front, lives of between 100 and 200 years are being projected for K3 inks especially when combined with spray-coated varnishes. PremierArt Spray has been the most tested at Wilhelm Research, but the DCP Giclée varnish has always offered a massive toughening of a surface, as well as both ozone and moisture protection. With DCP varnish, the most savage test we have heard of is from member, Andrew Williams, who spilled paint onto a varnished canvas and still got away with it via a turpentine-loaded rag – not recommended, but a spectacular test! DCP has also improved on one of the niggles with aqueous-based, paintedon varnishes, by the addition of an anti-foaming agent. Varnishes applied to stretched canvas both before and after are assisting in toughening up the surface to provide both abrasion resistance and edge-cracking resistance.

Metamerism has always been the bane of the printer’s life. For those who are unfamiliar with the term it describes the apparent colour shift when you move a print from one type of illumination to the other. It has always been more of a problem with pigment inks compared to dyes but as you read earlier, we don’t do dyes! Various solutions have been proposed, from specialist ink sets such as Permajet MonoChrome Pro and VT Blax, through to specialist RIPs which slice out the badly-behaving yellows. Epson has made massive strides in that the K3 ink set has reduced the metameric index by quite a way, whilst giving the photographer superb colour as well – this is vital for combined mono-colour effects on a portrait or album page. The introduction of the original Epson Gray Balancer in a user-friendly guise as Advanced Black and White is also most welcome. Making fine-tuned toning biases to your mono is now a piece of cake.

Ink-jet printing speeds have been improved such that we usually print at 2880dpi these days and to heck with the additional time! This is however, not for everybody and for balance we should point out that the specialist laboratories are now offering very competitive prices for high-quality digital printing to traditional media. They also have the edge when it comes to the gorgeous metallic finishes, which add such a lift to your album pages.

Looking to the future it seems unlikely that the paper chase will be called off just yet, the hounds are still hungry and there are no foxes to chase any more! With both Focus and Photokina to come, who knows what the future has in store – happy hunting!

Fade 7 All about the Lab

At the prompting of David Anthony Williams during a discussion at the Convention, we repeat and expand on how to interpret an error plot set out in Lab. Lab mode splits the components of a colour into three parameters, two of which deal with colour and the third which defines the lightness or darkness. They are the lightness value L, the a value which specifies the redness to greenness of the colour and b which defines the yellowness to blueness of the colour. Thus you divorce the lightness-darkness from colour and if you have an image of a person’s face lit from the side, the Lab a and b values will be the same on both cheeks (give or take a point) but the lightness value will change quite lot.

Using Lab makes assessment of colour easier as you can look at the colour elements (the colour – is it green or blue and the saturation – is it pure and vibrant or dull and neutral?). Small values of a and b represent colours close to the neutral point (a=0 b=0) large values of a and b represent strong vibrant colours. The actual mix of a and b determine the hue to define the colour as green, cyan, blue, etc.

There is no single measurement of goodness to describe how accurate a colour is perceived. The eye is most sensitive to changes in colour close to the neutrals and least sensitive to variations within the bright vibrant blues. Sensitivity around the Lab plot is variable. The error between two colours is a measure of the length of the line that connects them in the three dimensional Lab space – this is why we cannot show you the diagram on a flat page. To overcome the sensitivity close to the neutral and the goofy effects around the blues (for example) we use an additional measure called ÄE2000 which attempts to take care of the perceptual variations. Even when you have pinned down the measurement, you are not out of the water as the perception of the error is also size dependent and sometimes a small print looks OK but changes to being unacceptable when you blow it up into a larger print.

So – in summary:
1. Values from near the centre of the graph are more neutral.
2. Values found in places around the plane of the graph are different hues – when they are the same distance from the middle they are roughly the same saturation.
3. Values on the graph origin (the 0, 0 point) are neutral, black and neutral at the bottom and white and neutral at the top end, all shades of neutral grey in between.
4. The error between two colours is the length of the line within the 3-D graph – small lines are better!
5. It is never possible to show the 3-D graph in a magazine because it is flat.

What’s good and what’s bad?

1. Unprofiled printers deliver average error values between 15 and 25 and at this level look quite poor even to the untrained eye.

2. Colour-managed printers can usually get to between 9 and 12 points and can look quite good, providing the errors in the neutrals are low and that any colour bias in skin tones is not green.

3. Well-profiled printers deliver errors between 4 and 5 over most of the gamut (the deep blue sometimes drifts out to about 12).

4. Contract proofing is usually agreed at between 4 and 7 points.

5. Tuned profiles, and considerable care, can get error values down to 2 points but only experts, in perfect lighting conditions, tend to worry at this level.

6. Under perfect conditions a normally visioned person can detect a difference of about 1 Lab error point. That is making comparisons between two swatches, not between two pictures.

The SWPP 2008 Convention was an outstanding success,
we have 174 days to get ready for the 2009 convention - which starts on January 14, 2009

Photo Quote: You learn to see by practice. It's just like playing tennis, you get better the more you play. The more you look around at things, the more you see. The more you photograph, the more you realize what can be photographed and what can't be photographed. You just have to keep doing it.- Eliot Porter