ICC Profiles

 

After writing about colour management, printer (and monitor) calibration and printing the photographs, both theory and practice at Burton College and via D S Colour Labs, I thought I had better do a short blog on ICC Profiles.

The term ICC refers to the International Colour Consortium.

Understanding what a profile is will help you fully comprehend what happens in colour-managed transformations. An ICC profile is a standard way of numerically defining the way a particular device (a scanner, camera, printer or monitor) renders colour for a human observer under average daylight conditions. Colour management involves linking these various device profiles together in a way that allows us to control the appearance of colours from one device to another. In order for this to work, a profile must reference the observable colours from a device to a device-independent model, a sort of absolute definition of colour. Profiles are static definitions, and the dynamic calculations that move an image file through various profiles to arrive at the final output are handled by a colour management module (CMM) that’s the mathematical engine for all the transforms.

Therefore, a profile is a special number transformer, a kind of black box called a lookup table (LUT), or more often a colour lookup table (CLUT), which takes a set of numbers and returns another set of numbers. The first set of numbers can be from any kind of colour device (RGB, CMYK or grey scale); the second set of numbers is the LAB definition of the colour represented by the first set.

The above might look confusing, but it is important to remember that all computers work on binary, and that even that picture you took on location or in Burton College’s studio, is seen by the computer as simply a series of 1s and 0s.

A profile “looks up” the LAB value for a colour in a specific colour space.

You can think of LAB numbers as being independent of any particular device but representative of colours observable under D50 graphics industry-standard lighting. Therefore, a profile gives us a real colour definition of the numbers from a digital file—in D50 light.

Some profiles are relatively simple rules based on a matrix with a few points defining a larger set of colours. Other profiles are larger plots of all possible colours in a particular set. Matrix profiles are commonly used for Photoshop’s working spaces and monitor profiles. Printer profiles are most commonly larger CLUTs, sometimes referred to as table-based profiles. The math surrounding all this is staggering. For the artist, a profile is merely a definition of the colour rendered by a device translated into LAB. When photographers need to transform one set of device numbers into numbers for another device, they use profiles to “look up” the LAB colours and generate new numbers for the next device based on those colours.

LAB Colour is the link between the two device numbers.

When the profiles for the devices you’re using are installed, you simply have to select the appropriate profile at the right time to manage the necessary colour transforms.

Printer Calibration

The final element of the digital work flow, the printer, has to be calibrated to ensure that all you hard work, composition, capture, conversion / processing, etc, is not all in vain.

 

Photographs looking different when displayed as opposed when they are printed is not a new issue that has been created with the digital revolution.  Paul, my brother, used slide film for years because he liked how the colours were more vibrant and true to what he saw when he took the photograph, when they were shown on a slide projector,  in a similar way to how our images look on the screen, but when prints were taken off the slides the photographs lacked the vibrancy and punch that he saw when it was projected on to a screen, in the same way as our photographs lack these features when our photographs are printed out.

 

It is important to note thought that a calibration has to be carried out for each printer / ink / paper combination, so basically it is best to stick to one make of ink and one type (finish, weight and even manufacturer) of photographic quality paper.  Some papers are promoted as bright white in colour as opposed to just white.

 

Some photographic paper manufacturers, for example permajet, offer a service whereby the photographer buys a pack of their paper, they produce a print using their combination of printer / ink / with the manufacturer’s paper, and send this to the manufacturer who analyses the colours against the original image.  The manufacturer then sends a custom ICC profile for their paper when used with the photographer’s printer and ink.

 

The ICC profile for a printer is created by comparing a test print result using a photometer with the original reference file. The test chart contains known CMYK colours, whose offsets to their actual L*a*b colours scanned by the photometer are resulting in an ICC profile. Another possibility to ICC profile a printer is to use a calibrated scanner as the measuring device for the printed CMYK test chart instead of a photometer.

 

A number of manufacturers, like Huey, Eye-One, etc produce kits which can calibrate monitors and printers, using colour photometers, to maintain full colour management from the beginning of the workflow right through to the end print.

 

Some software, such as Adobe’s Photoshop has a soft proofing option that can be used to simulate on screen how the photograph will actually look on paper, colour and depth wise as opposed to a simple print preview, which just shows how the image would fit on the page.

 

Below is an example of how an image looked on the computer screen, and how it looked on the soft proofing simulation from Adobe Photoshop:

This example shows how prints can lack the punch that on screen images have.

 

The problem is that no matter how ‘bright white’ you paper might be, it would never look as bright as a monitor screen.

 

 

Using ICC profiles

 

When you choose the print option from Adobe Photoshop, you will get this requester:

 

When the print dialog comes up, make sure you have Colour Management selected in the drop-down at the upper-right corner; most of the important printing options for our purposes are in this area (Figure 4). This is where you set up all the Profile options for your prints.

At the centre of the dialog, Position controls how the image lays out on the page. The Centre Image check box provides a quick way to place the image. Directly below that is the Scaled Print Size area; by default, this is set up for 100%. If the image is way too small or way too big on the page preview, click the Print Settings button and make sure you’re using the right-sized paper. Checking the Scale To Fit Media check box is a quick and dirty method of sizing the image to fit the paper; just beware that your quality will suffer if the reported Scale percentage is overly high. It’s far better to set the size properly in Photoshop before using the dialog. The Bounding Box check box is useful when you have an area of white canvas in your image—the bounding box shows the edges of the image against the white of the paper.

 

The important colour settings reside in the right third of the dialog box. The two radio buttons directly under the Colour Management drop-down identify whether you’re going to print the document directly or generate a simulation proof; if you’re making prints for your portfolio or to sell to a client, you’ll probably check Document because this generally will provide the highest-quality print for your image. This sets the profile to the document colour space and determines from where the colour starts in its journey to the print.

Next is the Colour Handling area. For RGB images, the Colour Handling drop-down shows Photoshop Manages Colours, Printer Manages Colours or Separations.

 

Photoshop Manages Colours. Selecting Photoshop Manages Colours allows you to select the Printer Profile in the drop-down menu just below this one. This is the most straightforward way to set up colour management for the print. If you select Photoshop Manages Colours, remember to turn off colour management in the printer dialog!

 

Printer Manages Colours. If you select Printer Manages Colours, the Print Profile option will be greyed out, and you’ll have to set the Colour Management options in the printer driver. The Printer Driver dialogs are usually a lot more confusing in this regard, so you would be wise to stick with Photoshop.

 

Separations. Separations will be available only if you’re printing from a CMYK document; otherwise, it will be greyed out. This is used only when printing separate cyan, magenta, yellow and black “plates” or simulations, and for the most part, you can ignore it.  This type of printing is only really for use with printing companies who use the traditional plates method of printing.  Below is a screen grab from PhotoPlus with the colour separations and Prepress options:

 

The last choice is Rendering Intent. Here you can choose: Perceptual, Saturation, Relative Colorimetric or Absolute Colorimetric. 90% of the time, Relative Colorimetric will give you the best result. Occasionally, certain very saturated colours will tend to posterize and lose detail in the print. If this is the case, you can try to solve the problem with Perceptual rendering.

 

Generally though, Perceptual rendering will give a less saturated colour in the print, and your skin tones could become dull. The other renderings are applicable for custom profiles and unusual circumstances; however, for the most part, you can ignore them with people images.

 

Beginning with Photoshop CS5, the large preview in the dialog is colour managed and has some check-box controls underneath the preview. Checking Match Print Colours, by default, checks the other two boxes you can uncheck them if you desire. Gamut Warning renders flat areas of grey over any colour that’s out of gamut for the selected printer profile. Show Paper White puts a tone into the white areas of the preview in an attempt to simulate the effect of the paper colour on the image (much as you can with the Custom Proof Setup under the View Menu). The preview also can be used to reposition the image directly. If you uncheck the Centre Image check box in the Position area, you can click the image preview and move it around on the page and/or rescale it by dragging on the corner handles in the bounding box (if you uncheck the Bounding Box, you won’t be able to do this).

 

Once all your options are set, you’re free to click Print. The only additional thing you need to remember is that if your colour management options are being set in Photoshop, you have to turn off any such options in the Printer Driver dialog. All of the colour transformations will have taken place already in Photoshop before the data hits the printer driver, so make sure you don’t “double colour manage” and introduce an additional transformation. Every printer driver is a little different, but yours will have some option to select no colour management in the printer driver.

Monitor Calibration

 

When we use a computer (windows based, Mac, Linux, etc) we see everything via the computer’s monitor.  Whilst everything might look alright on the screen when creating documents, when it comes down to working with photographs, it can be another matter.

Ambient lighting, where you are working, is very important as it can lead to subtle differences, for example normal tungsten lighting can sometimes produce a slight colour cast, not only when taking the photographs, but later when you are working on them.  So it is important to make sure that the room in which you are working is well lit, not just for obvious health and safety purposes.

Basically there are two types of computer monitor CRT (the older bulky monitors) and LCD (flat screen monitors).

Whilst LCD monitors are becoming more common place, some do suffer from the problem that if it is viewed from an angle the colours do look different.

There are two methods of calibrating a monitor:

1. Visual
2. Mechanical

 

Visual Calibration

Visual involves either using the standard built in tools for setting the screen:

Some will choose to make use of more accurate colour calibration charts, which show a wide range of colours, and different levels of grey, can help detect more subtle colour differences:

Close together lines can be used to check for sharpness of the printer.  In fact the above chart is available for calibrating printers as well.

But visual calibration does rely on the eye of the photographer.

 

Mechanical Calibration

This type of calibration is more accurate, but can be very expensive.

There are tools like the Eye-One which can be used to calibrate both your computer monitor and your printer.

For calibrating the monitor a colorimeter is attached flat to the display's surface, having been shielded from all ambient light, to avoid errors caused by colour casts.

Below is the colorimeter from the Eye-One package analysing the red square on the computer monitor

The calibration software sends a series of colour signals to the display and compares the values that were actually sent against the readings from the calibration device. This establishes the current offsets in colour display. Depending on the calibration software and type of monitor used, the software either creates a correction matrix (i.e. an ICC profile) for colour values before being sent to the display, or gives instructions for altering the display's brightness/contrast and RGB values through the OSD. This tunes the display to reproduce fairly accurately the in-gamut part of a desired colour space.

Preparation for Printing

I have decided to produce two A3 prints, one from each section, via the college printer, and the remaining eighteen prints via D S Colour Labs.

The paper used at the college is HP Satin Matt A3+ 250g/m2 (Q5462A):

Specifications shown below:

for which their HP Photosmart B9180 printer is calibrated for.

Above the printer is a set of calibration charts that have been used during the calibration process, just in case there is a problem later, where the original charts can be compared to newly printed charts.

Because the printer is calibrated to suit the paper that the college request the students to use on this printer, the images should come out to match the image perfectly.

This paper will give a fine finish to the printed images, without reflection or glare, which I found when I had some prints for last year's exhibition, twenty-ten at the college.  The reflections that resulted as a result of using pearl finish paper, which is glossy, showed up any marks that were the results of the photograph being mounted, which I felt let down the final work.

The printers use genuine HP ink cartridges and are checked on a regular basis to prevent any common printing problems such as banding (horizontal lines), ink run (vertical lines) and general poor printing quality.

Printer Problems - Inkjet Printers

One thing about printing your work at home is that you have been in full control of the whole process from choosing your position and taking the photograph to seeing your print emerge from the printer. With this control though comes a few drawbacks including hardware and software issues.

As inkjet printers are the most common printers used at home for printing, I will cover this type of printer.

 

Most inkjet printers have a built-in diagnostics program to help you troubleshoot. Typically, running a test page involves pressing a button or two as you turn on the printer. Many inkjet printers also use a combination of indicator lights to help you pinpoint the problem.

 

Below are some of the problems that you could encounter at the printing stage:

Prints are lighter than expected or prints contain white spots or horizontal lines.

These signs point to a clogged print head - especially if you haven’t used your inkjet printer for some time. Banding (fine horizontal lines across the print are a common problem, sometimes encountered after changing a print cartridge.

Below is an example of banding:

 

To solve these problems select the printers cleaning and diagnostic utilities application for your printer, this is installed when you install your printer:

 

Below is the utilities screen for my Epson Stylus Colour 860:

 

 

Below is the utilities screen for my Canon Printer:

 

 

Then carry out a test print to verify if any of the print head nozzles are blocked:

 

 

If the resulting print has gaps in it then you need to run the head cleaning tool:

 

 

 

then carry out a test to ensure that the problem has been fixed.  If necessary repeat the cleaning and testing, until you are happy.  Bear in mind though that during the test print and cleaning cycles ink is used so beware if you are low on ink.

Vertical lines are jagged

This is usually a sign that the print head is out of alignment. There’s not much you can do to avoid this problem - all print heads become misaligned over time.

You can usually recalibrate the heads using the alignment tool that comes in your printer’s utility section. This involves printing a pattern of lines on normal paper and choosing which pattern looks best.

 

Below is a screen grab of the Epson print head alignment tool.

 

Colours look dull and sometimes run into each other

Check that you have loaded photo quality paper into the printer. I know this sounds odd but sometimes the printer may not catch the piece of photographic paper properly and feed through another sheet below if the photographic paper is not loaded properly. Also if the photographic paper is put in the wrong way around (some photographic paper, especially thinner matt you will be printing on the back of the paper which is not prepared for printing on.

In this case it is simply a case of checking what paper the printer has used and if it's the right way round.



Colours are missing or prints lack shadows and contrast

Colours may print inconsistently even before your printer instructs you to replace a cartridge. If the ink cartridges are low on ink when the problem occurs, try replacing them, this may improve colour quality.

If there’s enough ink but your print seems to be missing a particular colour, you probably have a clogged nozzle, so you’ll need to clean your print head. Colour quality can also suffer if ink cartridges have been in the printer for more than six months. Try swapping in a new cartridge.

Vertical lines down the print, either on the front or on the back

This means that at some stage ink has got onto the guide or rollers of the printer.

This means a lengthy cleaning, I use cotton wool buds, to clean the guides and rollers where the ink is coming from. Feed through the printer old printouts afterwards to check the guides and rollers are clean before printing again. If the guides and rollers are clean and you have the problem again there could be a serious fault with the printer.

Odd looking text being printed out instead of your photograph

This is usually a sign that there is a problem with the printer driver, which translates what the computer is sending to the printer to what is printed out.

If you're experiencing problems visit your inkjet printer manufacturer's web site and download the most current printer driver. Once you have reinstalled your printer software you will need to reboot your computer and then try printing again.

Paper constantly jamming

This can mean that there is something is blocking the path of the paper through the printer.

 

Check inside the printer for anything like torn paper, staples, paper clips etc. If a piece of paper jams inside the printer carefully remove it checking for any missing areas of paper, if this does happen check inside the printer for the missing paper and remove this as quick as possible.

Multiple pages fed through at once

This can either mean that the paper is sticking together, often through static, or that the paper thickness setting is set too thick.

 

Check the paper thickness setting, if there is one on the printer, and set it correctly, and remove the paper from the printer, fan the paper (to separate it) and re-insert the paper into the printer.

 

 

Colours do not match what you see on the screen

This is usually a case of not using any form of colour management.

Basically it is a case of setting up your camera, monitor and printer to interpret colours in the same way, so that skin tones come out correctly, matching what you actually saw before you took the photograph.

This might sound odd, but, I have noticed a distinct difference when printing out the same photograph on my Epson printer and Canon printer.  The Epson seems colder, with a slight green cast, whereas the Canon produces a warmer tone.

 

No print out at all

Check the printer queue or status monitor, to see if the print has gone to the printer, if you have more than one printer make sure it has gone to the correct printer:

often under the status heading a warning will appear if the printer is offline or out of paper or ink.

 

General Printer Care

Basically, it is a case of taking care of the printer,

• watching ink levels (many now have utilities that warn you when the ink is getting low) both on the printer (flashing LEDs) and sometimes on the computer (a window opening up).
• Make sure all connectors are in securely.
• carefully remove paper from the printer, if you have to pull the paper out, which could damage the paper feed mechanism, check that there are no missing pieces, which could lead to paper jams.
• only use good quality ink, poor quality ink will produce poor quality prints and may clog up the print heads
• only move the printer when you have to, certainly not when it is printing.
• Always keep plenty of ink, a spare cartridge of each if possible, because you never know you might run out of ink at a bad time, or late at night, trust me, I know !