Desktop Printing 101

Posted on February 10, 2014 by Andrew Astbury

Understanding Desktop Printing – part 1

Desktop printing is what all photographers should be doing.

Holding a finished print of your epic image is the final part of the photographic process, and should be enjoyed by everyone who owns a camera and loves their photography.

But desktop printing has a “bad rap” amongst the general hobby photography community – a process full of cost, danger, confusion and disappointment.

Yet there is no need for it to be this way.

Desktop printing is not a black art full of ‘ju-ju men’ and bear-traps – indeed it’s exactly the opposite.

But if you refuse to take on board a few simple basics then you’ll be swinging in the wind and burning money for ever.

Now I’ve already spoken at length on the importance of monitor calibration & monitor profiling on this blog HERE and HERE so we’ll take that as a given.

But in this post I want to look at the basic material we use for printing – paper media.

Print Media

A while back I wrote a piece entitled “How White is Paper White” – it might be worth you looking at this if you’ve not already done so.

Over the course of most of my blog posts you’ll have noticed a recurring undertone of contrast needs controlling.

Contrast is all about the relationship between blacks and whites in our images, and the tonal separation between them.

This is where we, as digital photographers, can begin to run into problems.

We work on our images via a calibrated monitor, normally calibrated to a gamma of 2.2 and a D65 white point. Modern monitors can readily display true black and true white (Lab 0 to Lab 100/RGB 0 to 255 in 8 bit terms).

Our big problem lies in the fact that you can print NEITHER of these luminosity values in any of the printer channels – the paper just will not allow it.

A papers ability to reproduce white is obviously limited to the brightness and background colour tint of the paper itself – there is no such think as ‘white’ paper.

But a papers ability to render ‘black’ is the other vitally important consideration – and it comes as a major shock to a lot of photographers.

Let’s take 3 commonly used Permajet papers as examples:

Permajet Gloss 271
Permajet Oyster 271
Permajet Portrait White 285

The following measurements have been made with a ColorMunki Photo & Colour Picker software.

L* values are the luminosity values in the L*ab colour space where 0 = pure black (0RGB) and 100 = pure white (255RGB)

Gloss paper:

Black/Dmax = 4.4 L* or 14,16,15 in 8 bit RGB terms
White/Dmin = 94.4 L* or 235,241,241 (paper white)

From these measurements we can see that the deepest black we can reproduce has an average 8bit RGB value of 15 – not zero.

We can also see that “paper white” has a leaning towards cyan due to the higher 241 green & blue RGB values, and this carries over to the blacks which are 6 points deficient in red.

Oyster paper:

Black/Dmax = 4.7 L* or 15,17,16 in 8 bit RGB terms
White/Dmin = 94.9 L* or 237,242,241 (paper white)

We can see that the Oyster maximum black value is slightly lighter than the Gloss paper (L* values reflect are far better accuracy than 8 bit RGB values).

We can also see that the paper has a slightly brighter white value.

Portrait White Matte paper:

Black/Dmax = 25.8 L* or 59,62,61 in 8 bit RGB terms
White/Dmin = 97.1 L* or 247,247,244 (paper white)

You can see that paper white is brighter than either Gloss or Oyster.

The paper white is also deficient in blue, but the Dmax black is deficient in red.

It’s quite common to find this skewed cool/warm split between dark tones and light tones when printing, and sometimes it can be the other way around.

And if you don’t think there’s much of a difference between 247,247,244 & 247,247,247 you’d be wrong!

The image below (though exaggerated slightly due to jpeg compression) effectively shows the difference – 247 neutral being at the bottom.

247,247,244 (top) and 247,247,247 (below) – slightly exaggerated by jpeg compression.

See how much ‘warmer’ the top of the square is?

But the real shocker is the black or Dmax value:

Portrait White matte finish paper plotted against wireframe sRGB on L*ab axes.

The wireframe above is the sRGB colour space plotted on the L*ab axes; the shaded volume is the profile for Portrait White. The sRGB profile has a maximum black density of 0RGB and so reaches the bottom of vertical L axis.

However, that 25.8 L* value of the matte finish paper has a huge ‘gap’ underneath it.

The higher the black L* value the larger is the gap.

What does this gap mean for our desktop printing output?

It’s simple – any tones in our image that are DARKER, or have a lower L* value than the Dmax of the destination media will be crushed into “paper black” – so any shadow detail will be lost.

Equally the same can be said for gaps at the top of the L* axis where “paper white” or Dmin is lower than the L* value of the brightest tones in our image – they too will get homogenized into the all-encompassing paper white!

Imagine we’ve just processed an image that makes maximum use of our monitors display gamut in terms of luminosity – it looks magnificent, and will no doubt look equally as such for any form of electronic/digital distribution.

But if we send this image straight to a printer it’ll look really disappointing, if only for the reasons mentioned above – because basically the image will NOT fit on the paper in terms of contrast and tonal distribution, let alone colour fidelity.
It’s at this point where everyone gives up the idea of desktop printing:

It looks like crap
It’s a waste of time
I don’t know what’s happened.
I don’t understand what’s gone wrong

Well, in response to the latter, now you do!

But do we have to worry about all this tech stuff ?

No, we don’t have to WORRY about it – that’s what a colour managed work flow & soft proofing is for.

But it never hurts to UNDERSTAND things, otherwise you just end up in a “monkey see monkey do” situation.

And that’s as dangerous as it can get – change just one thing and you’re in trouble!

But if you can ‘get the point’ of this post then believe me you are well on your way to understanding desktop printing and the simple processes we need to go through to ensure accurate and realistic prints every time we hit the PRINT button.

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Pixel Resolution – part 2

Posted on December 15, 2013 by Andrew Astbury

More on Pixel Resolution

In my previous post on pixel resolution I mentioned that it had some serious ramifications for print.

The major one is PHYSICAL or LINEAR image dimension.

In that previous post I said:

Pixel dimension divided by pixel resolution = linear dimension

Now, as we saw in the previous post, linear dimension has zero effect on ‘digital display’ image size – here’s those two snake jpegs again:

Andy Astbury,wildlife in pixels,pixel,dpi,ppi,pixel resolution,photoshop,lightroom,adobe

European Adder – 900 x 599 pixels with a pixel resolution of 300PPI

European Adder – 900 x 599 pixels with a pixel resolution of 72PPI

Digital display size is driven by pixel dimension – NOT linear dimension or pixel resolution.

Print on the other hand is directly driven by image linear dimension – the physical length and width of our image in inches, centimeters or millimeters.

Now I teach this ‘stuff’ all the time at my Calumet workshops and I know it’s hard for some folk to get their heads around print size and printer output, but it really is simple and straightforward if you just think about it logically for minute.

Let’s get away from snakes and consider this image of a cute Red Squirrel:

Red Squirrel with Bushy Tail – what a cutey!
Shot with Nikon D4 – full frame render.

Yeah yeah – he’s a bit big in the frame for my taste but it’s a seller so boo-hoo – what do I know ! !

Shot on a Nikon D4 – the relevance of which is this:

The D4 has a sensor with a linear dimension of 36 x 24 millimeters, but more importantly a photosite dimension of 4928 x 3280. (this is the effective imaging area – total photosite area is 4992 x 3292 according to DXO Labs).

Importing this image into Lightroom, ACR, Bridge, CapOne Pro etc will take that photosite dimension as a pixel dimension.

They also attach the default standard pixel resolution of 300 PPI to the image.

So now the image has a set of physical or linear dimensions:

4928/300 x 3280/300 inches or 16.43″ x 10.93″

417.24 x 277.71 mm for those of you with a metric inclination!

So how big CAN we print this image?

Pixel Resolution & Image Physical Dimension

Let’s get back to that sensor for a moment and ask ourselves a question:

“Does a sensor contain pixels, and can it have a PPI resolution attached to it?

Well, the strict answer would be No and No not really.

But because the photosite dimensions end up being ‘converted’ to pixel dimensions then let’s just for a moment pretend that it can.

The ‘effective’ PPI value for the D4 sensor could be easily derived from its long edge ‘pixel’ count of the FX frame divided by the linear length which is just shy of 36mm or 1.4″ – 3520 PPI or thereabouts.

So, if we take this all literally our camera captures and stores a file that has linear dimensions of 1.4″ x 0.9″, pixel dimensions of 4928 x 3280 and a pixel resolution of 3520 PPI.

Import this file into Lightroom for instance, and that pixel resolution is reduced to 300 PPI. It’s this very act that renders the image on our monitor at a size we can work with. Otherwise we’d be working on postage stamps!

And what has that pixel resolution done to the linear image dimensions? Well it’s basically ‘magnified’ the image – but by how much?

Magnification & Image Size

Magnification factors are an important part of digital imaging and image reproduction, so you need to understand something – magnification factors are always calculated on the diagonal.

So we need to identify the diagonals of both our sensor, and our 300 PPI image before we can go any further.

Here is a table of typical sensor diagonals:

Table of Sensor Diagonals for Digital Cameras.

And here is a table of metric print media sizes:

Metric Paper Sizes including diagonals.

To get back to our 300 PPI image derived from our D4 sensor, Pythagoras tells us that our 16.43″ x 10.93″ image has a diagonal of 19.73″ – or 501.14mm

So with a sensor diagonal of 43.2mm we arrive at a magnification factor of around 11.6x for our 300 PPI native image as displayed on our monitor.

This means that EVERYTHING on the sensor – photosites/pixels, dust bunnies, logs, lumps of coal, circles of confusion, Airy Discs – the lot – are magnified by that factor.

Just to add variety, a D800/800E produces native 300 PPI images at 24.53″ x 16.37″ – a magnification factor of 17.3x over the sensor size.

So you can now begin to see why pixel resolution is so important when we print.

How To Blow Up A Squirrel !

Let’s get back to ‘his cuteness’ and open him up in Photoshop:

Our Squirrel at his native 300 PPI open in Photoshop.

See how I keep you on your toes – I’ve switched to millimeters now!

The image is 417 x 277 mm – in other words it’s basically A3.

What happens if we hit print using A3 paper?

Red Squirrel with Bushy Tail. D4 file at 300 PPI printed to A3 media.

Whoops – that’s not good at all because there is no margin. We need workable margins for print handling and for mounting in cut mattes for framing.

Do not print borderless – it’s tacky, messy and it screws your printer up!

What happens if we move up a full A size and print A2:

Red Squirrel D4 300 PPI printed on A2

Now that’s just over kill.

But let’s open him back up in Photoshop and take a look at that image size dialogue again:

Our Squirrel at his native 300 PPI open in Photoshop.

If we remove the check mark from the resample section of the image size dialogue box (circled red) and make one simple change:

Our Squirrel at a reduced pixel resolution of 240 PPI open in Photoshop.

All we need to do is to change the pixel resolution figure from 300 PPI to 240 PPI and click OK.

We make NO apparent change to the image on the monitor display because we haven’t changed any physical dimension and we haven’t resampled the image.

All we have done is tell the print pipeline that every 240 pixels of this image must occupy 1 liner inch of paper – instead of 300 pixels per linear inch of paper.

Let’s have a look at the final outcome:

Red Squirrel D4 240 PPI printed on A2.

Perfick… as Pop Larkin would say!

Now we have workable margins to the print for both handling and mounting purposes.

But here’s the big thing – printed at 2880+ DPI printer output resolution you would see no difference in visual print quality. Indeed, 240 PPI was the Adobe Lightroom, ACR default pixel resolution until fairly recently.

So there we go, how big can you print?? – Bigger than you might think!

And it’s all down to pixel resolution – learn to understand it and you’ll find a lot of the “murky stuff” in photography suddenly becomes very simple!

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How White is Paper White?

Posted on December 2, 2013 by Andrew Astbury

What is Paper White?

We should all know by now that, in RGB terms, BLACK is 0,0,0 and that WHITE is 255,255,255 when expressed in 8 bit colour values.

White can also be 32,768: 32,768: 32,768 when viewed in Photoshop as part of a 16 bit image (though those values are actually 15 bit – yet another story!).

Either way, WHITE is WHITE; or is it?

Take this Arctic Fox image – is anything actually white? No, far from it! The brightest area of snow is around 238,238,238 which is neutral, but it’s not white but a very light grey. And we won’t even discuss the “whiteness” of the fox itself.

The Hen Pheasant above was shot very late on a winters afternoon when the sun was at a very low angle directly behind me – the colour temperature has gone through the roof and everything has taken on a very warm glow which adds to the atmosphere of the image.

We can take the ‘snow at sunset’ idea even further, where the suns rays strike the snow it lights up pink, but the shadows go a deep rich aquamarine blue – what we might call a ‘crossed curves’ scenario, where shadow and lower mid tones are at a low Kelvin temperature, and upper mid tones and highlights are at a much higher Kelvin.

All three of these images might look a little bit ‘too much’ – but try clicking one and viewing it on a darker background without the distractions of the rest of the page – GO ON, TRY IT.

Showing you these three images has a couple of purposes:

Firstly, to show you that “TRUE WHITE” is something you will rarely, if ever, photograph.

Secondly, viewing the same image in a different environment changes the eyes perception of the image.

The secondary purpose is the most important – and it’s all to do with perception; and to put it bluntly, the pack of lies that your eyes and brain lead you to believe is the truth.

Only Mother Nature, wildlife and cameras tell the truth!

So Where’s All This Going Andy, and What’s it got to do with Paper White?

Fair question, but bare with me!

If we go to the camera shop and peruse a selection of printer papers or unprinted paper samplers, our eyes tell us that we are looking at blank sheets of white paper; but ARE WE?

Each individual sheet of paper appears to be white, but we see very subtle differences which we put down to paper finish.

But if we put a selection of, say Permajet papers together and compare them with ‘true RGB white’ we see the truth of the matter:

Paper whites of a few Permajet papers in comparison to RGB white – all colour values are 8bit.

Holy Mary Mother of God!!!!!!!!!!!!!!!!

I’ll bet that’s come as a bit of a shocker………

No paper is WHITE; some papers are “warm”; and some are “cool”.

So, if we have a “warmish” toned image it’s going to be a lot easier to “soft proof” that image to a “warm paper” than a cool one – with the result of greater colour reproduction accuracy.

If we were to try and print a “cool” image on to “warm paper” then we’ve got to shift the whole colour balance of the image, in other words warm it up in order for the final print to be perceived as neutral – don’t forget, that sheet of paper looked neutral to you when you stuck it in the printer!

Well, that’s simple enough you might think, but you’d be very, very wrong…

We see colour on a print because the inks allow use to see the paper white through them, but only up to a point. As colours and tones become darker on our print we see less “paper white” and more reflected colour from the ink surface.

If we shift the colour balance of the entire image – in this case warm it up – we shift the highlight areas so they match the paper white; but we also shift the shadows and darker tones. These darker areas hide paper white so the colour shift in those areas is most definitely NOT desirable because we want them to be as perceptually neutral as the highlights.

What we need to do in truth is to somehow warm up the higher tonal values while at the same time keep the lowest tonal values the same, and then somehow match all the tones in between the shadows and highlights to the paper.

This is part of the process called SOFT PROOFING – but the job would be a lot easier if we chose to print on a paper whose “paper white” matched the overall image a little more closely.

The Other Kick in the Teeth

Not only are we battling the hue of paper white, or tint if you like, but we also have to take into account the luminance values of the paper – in other words just how “bright” it is.

Those RGB values of paper whites across a spread of Permajet papers – here they are again to save you scrolling back:

Paper whites of a few Permajet papers in comparrison to RGB white – all colour values are 8bit.

not only tell us that there is a tint to the paper due to the three colour channel values being unequal, but they also tell us the brightest value we can “print” – in other words not lay any ink down!

Take Oyster for example; a cracking all-round general printer paper that has a very large colour gamut and is excellent value for money – Permajet deserve a medal for this paper in my opinion because it’s economical and epic!

Its paper white is on average 240 Red, 245 Green ,244 Blue. If we have any detail in areas of our image that are above 240, 240, 240 then part of that detail will be lost in the print because the red channel minimum density (d-min) tops out at 240; so anything that is 241 red or higher will just not be printed and will show as 240 Red in the paper white.

Again, this is a problem mitigated in the soft proofing process.

But it’s also one of the reasons why the majority of photographers are disappointed with their prints – they look good on screen because they are being displayed with a tonal range of 0 to 255, but printed they just look dull, flat and generally awful.

Just another reason for adopting a Colour Managed Work Flow!

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