Colour Profiling and Soft Proofing

With the mass uptake of digital imaging, home computing, portable devices and online publishing, it has become more important than ever to ensure that images appear correctly on a range of devices.

As well as this, there is the issue of ensuring what is visible on your screen is what actually comes out of a printer or comes back from the printers you sent work to. This subject is perhaps the most complex and difficult to understand . . Once you understand this concept, you’ll no longer have any colour issues.

The solution is Colour Profiling. A colour profile is a small file, called an ICC (International Colour Consortium) file, and its job is to translate colour from one device to another in such a way as to ensure consistency between devices and colour spaces.

Step 1 is to always ensure you are working on a monitor that is calibrated. Calibrating a monitor is essential for accurate work, as developing your images on a screen that is, for argument’s sake, too blue or cold, will force you to make your images warmer in order to look correct on your screen. However, when sent to a printer, this will result in images that are excessively warm. We will look at how to actually profile a screen later , but for now, all colour critical work should be done on a screen that is profiled. The first thing you should be doing is ensuring that the monitor profile for that screen is active.

This will ensure that your Mac’s screen is accurately calibrated for White point (greys are actually neutral), gamma (how tones are spread from dark to light – all modern Macs and PCs use a gamma of 2.2), and Luminance (Brightness – measured in Candelas, or candle power… a range of 90 to 120cd/m2 is usual). If you are working at home, you will need to book out the screen calibrator and profile your home screen. We use the X-Rite Color Munky, but others are available, such as the DataColor Spyder series, the X-Rite i1 Display series. Any serious image maker should take colour accuracy seriously, and your computer monitor should be thought of as just as important as your cameras and lenses.. if not more so, as a poorly set up system will mean images can be too dark, light, or have inaccurate colour and/or contrast.

If calibrating a laptop, you should disable anything that changes the screen’s brightness with ambient lighting conditions or anything that automatically alters the screen’s settings. Once a screen is calibrated, it should NOT be adjusted at all. If you adjust the screen visually after calibration, you may as well not have calibrated in the first place. Step 2 is to ensure that Photoshop is set up to use the correct colour space, and to handle profile mismatches. (see next page) 3 In Edit/Color Settings make sure “Europe Prepress 3” is selected, and make sure “more options” is selected. Ensure that ALL profile mismatch boxes are ticked. In short, make sure it looks like the image Below. (See next page) 4 Photoshop CC, PC version This will ensure that A) Adobe RGB 1998 is the default colourspace, and B) Any image not embedded with Adobe RGB1998 will prompt you to change it to Adobe RGB1998 before editing, and when pasting an image that’s not Adobe RGB1998 into a document that is, will also prompt you to convert it before doing so.

Following these two steps will ensure that you are working in a sensible colour managed way, as a calibrated screen allows you to make accurate judgements on colour, and setting up PS is this way ensures that all mis-profiled image are converted to Adobe RGB1998 in order to work on them.

5 We’ll now look at why colour profiles are important. There are two main colour spaces that photographers use: Adobe RGB and sRGB. Their full names in order to find them should you need to are: Adobe RGB1998 sRGB IEC61966-2.1 These two colourspaces are available on both Mac and PC for all Adobe CC application, and should also be part of the Windows and Mac operating systems. (There is another profile often found called “Pro Photo” but this is a very wide colourspace that no screen yet invented can show, so avoid suing it – there’s no point) To fully understand the need for colour profiling, we have to understand how computers create colour. Colour on a computer is made up of Red, Green and Blue.

Most images when working on them in Photoshop are either 8bit (24bit) or 16bit (48bit). Image bit depths are referred to either by Bits per pixel (8bit) or the overall bit depth across all three channels. So as a ll we as photographers use are RGB, an 8bit image is sometimes referred to as 24bit. (3x 8 = 24) So using an 8bit image as an example: A digital signal is a binary signal which is either on or off… or 1 or 0. So a single bit (1bit) image will only have two states (and hence 2 colours) – black or white, or black and a single other colour, so if each colour channel (R,G,B) had only 1bit of data, each channel could only ever be black, or fully red, fully green or fully blue. As mixing R,G and B in equal measures results in white.. a 1bit RGB (3 bit) image is only ever made up of black or white. An 8bit image (such as a full colour JPEG) has 8 bits per pixel, so thinking in binary again, it has many more values available. As 1 bit image could only be 0 or 1, an 8bit images could be 00000000… or 11111111… or 01101001… or any combination of values of those 8 bits. In fact, there are 256 possible combinations of those binary bits, so there are 256 possible values per channel, or more importantly, 256 shades of red, green or blue. To explain: 8 bits per pixel available. Each bit can only ever be 0 or 1 (2 states.. on or off) so 2x2x2x2x2x2x2x2 = 256. This is referred to as “two to the power of eight”, or 28. Try it on a calculator. As each pixel is 8bits or Red, Green and Blue, the total bit depth is 24bit (8+8+8 = 24).

The total number of colours in a 8bit image is 16,777,216. We arrive at this figure the same way as above: There are 256 colours per pixel, and three channels per pixel, so 256x256x256 = 16777216 (256 to the power of 3 or 2563). So if all JPEG images for example are 8bit, why can they look different on different computers? 6 This is where the concept of colour profiling becomes important. Take the red channel of a 8bit image such as any JPEG you care to download from the internet. We know that it can have 256 levels per channel, so looking only at the red channel for the moment, it can be anywhere from Black (0) to fully red (255).

If we have a red pixel with a value of 255, what that is saying, if we could translate it to English, is “Make this pixel as red as you can”. The computer will do just that, and send it to the monitor. The problem arises because “maximum” red may not be the same for all screens. Some screens can display more vivid reds (or blues, or greens) than others and without colour profiling the computer has no way of knowing just how red that red will be on screen when told to make it “as red as possible”. To keep things simple, most monitors are created to adhere (roughly) to two main Colourspaces: Adobe RGB1998 or sRGB IEC61966-2.1. A colourspace is the “range” of how saturated colours are when told to be “maximum”. These are represented often as chromaticity charts, and you may have seen some: They look like this. They show the range of colours a monitor can display; often referred to as the screen’s “gamut”.

The Adobe RGB colourspace is wider, and allows more saturated colours than sRGB. However, not all displays can show Adobe RGB. 7 Most cheaper monitors and most laptop monitors can only show roughly the same colourspace as sRGB, so making something as “red as possible” will result in something that may look acceptable on a sRGB “standard gamut” monitor, but excessively red on a “Wide gamut” monitor. This is the problem. Without colour management, images that may look fine on a standard sRGB monitor will look very over-saturated on a wider gamut screen. In short, how colourful the image looks is dependent on the screen, and NOT the image itself, and as every monitor is different, the image may look different on every single un-calibrated monitor when not colour managed.

The most basic way you can control this is to limit the colourspace dependent upon where the images are likely to be seen, which essentially boils down to either in print, or on screen. For putting image on the internet, it makes perfect sense to limit the range of colours to sRGB, so you would save a version of the image especially for internet use embedded with the sRGB profile. Most devices are set by default to use sRGB as the default colourspace, so if you embed your images with sRGB as the ICC profile, then most devices will limit the amount of saturation in colours so as to look reasonably accurate on a wide range of devices.

The danger is NOT saving the image with a colour profile at all, or the wrong profile for its use. Edit/Convert to Profile. (see next page) 8 Then set the destination RGB space to sRGB IEC61966-2.1 Then click OK, and save the image using File/Save As to prevent saving over your original. 9 This image will now be more likely to display correctly as most devices and operating systems are set to use sRGB as the default colourspace, and even on a Wide Gamut monitor, if the browser or program uses colour management, the colours will be translated to the same as you saw it on your screen. For print you should convert the image to Adobe RGB1998, or if sending files away to print, whatever profile your printer suggests you should use.

If you set up Photoshop , Adobe RGB1998 already be your default working colourspace. Colour of files work by changing the RGB numbers in a file to make sure the actual perceived colours remain the same. If you take a colour swatch showing R255, G0, B0 (full red) for an image set up as sRGB. If I pick up the dropper tool and measure its RGB values we can see this is the case. If I save this file ensuring that the embedded profile is sRGB…. And then reload it; Photoshop will prompt me that it is not Adobe RGB1998 (if your colour settings are correct). (See next page) 10 If we select “Convert the document’s colours to the working space” it will open in an Adobe RGB1998 colourspace. The image should look identical to how it did in sRGB, but…. If we know measure the RGB values using the dropper tool, something interesting has happened. The value for red is no longer 255, but 218. This is because if not profiled, it would have just translated straight through as Red 255, and as there is more red available in Adobe RGB1998, it would have appeared redder.

This is how colour profiling works, by changing the RGB values to maintain accurate perceived colour. The result is the two reds appear identical (assuming the monitor is calibrated). Colour profiling always tried to maintain (wherever possible) the correct appearance of colour, and places no importance upon the RGB numbers. If the image was not embedded with a colour profile, every computer it is viewed upon would just have told the monitor to make it as red as possible and the file would just be expanded to fill the available colourspace, and that would mean how red it was is determined by the screen’s available gamut. On a wide gamut screen it would have been unbelievably saturated, yet on a narrow gamut screen it may have looked no different from the original sRGB file. The opposite is also true.

Embedding an image with Adobe RGB and putting it online can make the colours weak when viewed in a non-colour managed environment. 11 So how do you know what colour will look like in any given profile? Fortunately Photoshop allows you to view an image under the conditions of any ICC profile. It is referred to as Soft Proofing. If you have created an image with really deep blacks, but intend to print it on a paper that cannot produce a full black, then you will not be able to correctly adjust that image for that printing process. However, if the printer has a ICC profile created for that paper, the paper’s colour space will be reproduced if you use that profile.

Here’s a scenario: I have produced an image working in Adobe RGB1998 as my default working space, and saved that as my master, archived and finished version. I wish to send this off to be printed, and chose to send it to The Printspace, a well-known online printing service, how would I know what my prints would look like when they come back? Most decent printing services will either ask you to submit in sRGB and they will make the adjustments required for their printers, or they will allow you to download an ICC profile for the paper of your choice. The Printspace, like many others allow you do download a profile for their papers.

https://www.theprintspace.co.uk/ThePrintSpace/assets/profiles.zip Once downloaded and unzipped, you will have a folder that contains all Printspaces paper profiles. To install a profile on a PC, right click it and select install. On a Mac, it is more complicated, and the ICC profile will need to be manually copied to Library/Colorsync/Profiles. However, from 10.7.3 onwards, this folder is hidden by default, making it very difficult for the inexperienced to install profiles. If this applies, launch a terminal window (applications/Utilities/Terminal) and type chflags nohidden ~/Library 12 Then reboot the system.

Screen Shot 2016-04-25 at 18.57.30Once the profile for your chosen paper is installed, you can then soft proof your images using this profile to see how they will look. Because subtle changes may be made to the image, it is always best to convert the image to 16bit by using Image/Mode/16bit. Once your image is open in Photoshop, use View/Proof Setup/Custom • Select the device/paper to simulate in the “Device to Simulate” drop down. • DO NOT select preserve RGB Numbers. (As discussed on p.9, this is how profiles work, by changing numbers to preserve colours) • Ensure Black Point Compensation is checked. • Ensure “Preview” is checked. • DO NOT check anything in Display options.

Screen Shot 2016-04-25 at 18.58.28

The one variable control here is whether to select Perceptual or Relative Colorimetric for rendering intent. 13 Do NOT select anything other than these two options. Click OK to soft proof. Relative Colorimetric will simply clip out any out of gamut colours, so anything that’s too saturated for the paper or anything too dark to print will just be removed. This option has the least visible effect on the image, but can harm shadow detail if there are fine, subtle details in the shadows, and can effect very saturated colours. Perceptual will translate all colours, even those out of gamut or too dark to print to within the visible range of colours available in the paper. This has the most visible effect on appearance, especially in shadow areas that will nearly always appear lighter.

Screen Shot 2016-04-25 at 18.58.32

The idea is, that once soft proofed you can make adjustments to ensure the profiled image is the same as the original Adobe RGB or sRGB image. Before adjusting, ensure the soft proof is active by looking at the image name tab. If soft proof is active, it will also show the name of the ICC profile being used.. Not soft proofed Soft proofed The idea is to make adjustments to get the profiled image as close as possible to the original. Which rendering intent? Anything with fine, subtle shadow detail should be soft proofed in Perceptual, and adjustments made to match the appearance and shadow detail retained. You can quickly switch soft proofing off and on again at any time by suing CTRL+Y (Cmd+Y on mac). Once adjustments have been made to match the soft proofed image to the original, you are ready to actually embed the image with the profile by using Edit/Convert to Profile. (see next page) 14 IMPORTANT! If you soft proofed with Perceptual, you MUST embed the profile using the same rendering intent. If you soft proofed with perceptual, and then embed the profile with Relative Colorimetric, the image will come back too dark. Whichever rendering intent you used to soft proof, you must also use to embed the profile. Important! Never use Edit/Assign Profile when converting an image to a destination profile. Always use Edit/Convert to Profile. Finally, save a copy of the file to be printed using File/Save As and making sure the chosen profile is shown, and checked.

Screen Shot 2016-04-25 at 18.59.03

Be careful to NOT save over your original, as converting to a colour profile is a one way process and cannot be undone. Use a different file name. My advice is amend the file name with the profile, for example: Yourfilename_Fuji-C-Type_matt.tiff If your screen is correctly profiled, this method should result in consistent results.

Screen Shot 2016-04-25 at 19.04.26.png

 

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