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color calibration

Colour Calibration

Colour space or gamut:

  • each device such as camera, scanner, monitor or printer has limits as to which colours it can represent or detect, thus in our digital world, we can decide on which color space or gamut (ie. the range of colours) we wish to work in.
  • the most commonly used colour spaces are sRGB and Adobe RBG (1998).
  • sRGB is usually the current default for most systems as it is essentially the lowest common denominator and will result in reasonable appearance on computer monitors (ie. what you and everyone else can see on computers and across the internet).
  • Abobe RGB (1998) has a wider gamut than sRGB, in particular, it can contain colour data for richer cyan-green midtones, orange-magenta highlights, or green shadows than can sRGB.
    • why not just use Adobe RGB then?
      • unfortunately, most computer monitors cannot display the Adobe RGB gamut and thus some colours will be “out of gamut” and not displayed correctly which can give less than satisfactory viewing on the computer.
      • most low-end or consumer ink jet printers will only print sRGB gamut, thus to make use of Adobe RGB's wider gamut, the main benefit will be when printing to a high end ink jet printer or CYMK printer, and then only if your image contains those colors not available in sRGB but within Adobe RGB and within the colour gamut of the printer.
  • for those wanting the widest colour gamut and who intend to print to the latest high end printers which can make use of this wider color space, there are other wider colour spaces such as ProPhoto RGB.
  • FORTUNATELY for us photographers, as long as we shoot our digital photos in RAW files, the raw data can be converted to a wide gamut later, even the ProPhotoRGB.
  • UNFORTUNATELY for photographers who only shoot JPEGs, you will be stuck forever in a small colour space (usually sRGB, although possibly Adobe RGB if you select it on the camera prior to taking the photo), and worse, you will be confined to only 256 tones for each colour channel which will be limiting, particularly if you want to edit your photos. THUS IF A PHOTO IS LIKELY TO BE IMPORTANT TO YOU, STRONGLY CONSIDER SHOOTING IN RAW MODE - it also makes white balance corrections easier.
  • IF your prime aim is high end prints, then working in Adobe RGB may be better than sRGB.
  • IF your prime aim is display on computer or on the internet then you will be best with sRGB.
  • most ink jet printers are unable to print the more saturated blues that either sRGB or Adobe RGB can hold.

Colour calibration:

Choice of monitor:

  • you need to ensure that your monitor can display the color gamut reliably, unfortunately, most LCD monitors fall short and worse, the tone (actually the gamma) alters depending on the angle you view it, even from the top of the screen to the bottom of the screen when looking at it perpendicular can markedly effect the displayed tone.
  • monitors tend to be the weakest link in the chain of colour management.
  • Due to color shift over time, expect your CRT monitor to hold up to daily use for about 4 to 6 years.  After that, it will become dark, too bright, or so far out of balance that it cannot be profiled.
  • in 2006: 
    • try La Cie electron blue IV, Mitsubishi Diamond Pro 930 w/ SpectraView or Sony Artisan monitors
    • for the best results consider a NEC spectraview 2180 LED reference which uses more stable LED technology.

Calibrating your monitor:

  • most people aim to calibrate their monitors to Gamma 2.2 and 6500K as a standard which is in line with sRGB standards.
  • if you have more than one monitor, it is very useful to be able to have them both calibrated to the same standard so that if you edit an image using one, it should look the same on the other.
  • professional photographers calibrate at least once a month and before any major job, home users may consider every 4-8 weeks as monitors do drift over time and the hardware calibration method only takes about 10min to do. Calibration should be done after 30min of turning it on as colours change in the initial warm up period.
  • a typical profiling kit will include some easy to use software and a small USB “puck” colorimeter that you place on your screen and measure the specific red green and blue values that the software puts up during it's 4 to 7 minute calibration procedure.
  • consider purchasing the Gretag Macbeth Eye One Display V2  and consider Pantone's Huey which works with Gretag Macbeth's product to continually adjust your monitor as ambient lighting changes.
    • if you intend printing with your own printer, then get the upgrade to Eye-One Design, Photo, Proof or XT which allow printer profiling as well (see below) 
  • for the less specialist operators, consider either:
    • X-rite Huey monitor color correction - but does not have mechanism to check if monitor still calibrated, thus must run full calibration each time, but cheap at ~$A110 from DES
    • ColorVision Spyder3 from Kayell
    • Monaco Optix XR 
    • LaCie Blue Eye
  • alternatively, if you have Adobe Photoshop, you can use Adobe Gamma software utility to do a visual calibration.
  • if you really can't afford this, set monitor to Gamma 2.2, 6500K white point and at the very least use your eyes to check you can see all the segments in these test strips:

Calibrating your printer:

  • each printer will produce prints that appear different depending upon:
    • printer
    • printer inks - some printers allow a choice of ink styles or 3rd party inks
    • paper
    • printing software colour management settings
    • embedded colour profile within the image
    • ambient light when looking at the print
    • and when comparing it with what is seen on the monitor - also depends on monitor calibration (see above)
  • there are 3 main methods to get a ICC profile for your printer / paper / ink combination:
    • use a ready made printer ICC profile
      • this is OK if you use the printer manufacturer's recommended ink and paper
    • use a software-only profiling method based on known printers
      • this is OK if the software knows about your printer / paper / ink combination
      • eg. Colorvision PrintFix Plus (comes with CV Spyder 2 kits)
    • measure the actual colors printed from a test chart
      • this is the most versatile method
      • eg. 
        • Eye-One Photo (~$A2599) 
          • NB. the cheaper Eye-One Design's Easy chart apparently is not accurate enough to adequately create a accurate printer profile
          • Eye-One Photo can also create profiles for scanners and projectors, and in the SG version, can create profiles for digital cameras although most photographers will not need to do this.
          • based on the Datacolor 1005 spectrocolorimeter
          • get the Spyder 3 Studio which also includes Spyder 3 Elite monitor calibrator. 
  • more information on the net:

Calibrating your RAW development color in Lightroom using an Xrite ColorChecker Passport

  • camera sensors can change the way they output colour depending upon ambient lighting and even ISO, and even using a different lens can change the color
  • using a calibrated color swatch such as the Color Checker will help you create accurate colors consistently irrespective of which camera or lens you use, and this could be critical, especially when using composited images in Photoshop
  • in general, they still require you to take an accurate white balance corrected shot using a spectrally flat neutral white balance target BEFORE taking the shot of the color swatch - HOWEVER, the Xrite Color Checker Passport LR plugin software will do this automatically for you in Lightroom when it creates the profile
  • the Xrite Color Checker Passport is $US99 and the size of a passport and a very handy tool if color calibration or accurate white balance of your subject lighting is important to you BUT ONLY works with editing tools compatible with DNG files (eg. Adobe suite BUT NOT Capture One or DxO)
  • take a photo of the color checker with it facing your light source
  • in Lightroom, use this RAW file to create a Lightroom camera profile
  • these swatches should be replaced every 2 years as the color accuracy may fall due to fading with exposure to UV light

Calibrating your image editing software using ICC profiles:

  • in PS, you will need Photoshop 7, CS or CS2 or higher to use these profiles.
  • your printer hopefully will provide a printer color profiling service
    • accurate printer profiles combined with an accurate hardware calibrated monitor allows you to accurately “soft proof” your print BEFORE you waste money and time printing it.
    • the goal of a profile is NOT to make a perfect screen to print match. It's goal is to give you the best ability to 'soft-proof' for your printer's output and to take best advantage of your printer's physical gamut.
    • Photoshop now accurately informs us which colours in an image are in or out of the gamut of our printer.
    • you can then create a version of your file that specifically targets a given printer, paper and ink combination.
    • despite this, the printer may still not be able to reproduce certain tones such as highly saturated colors that your monitor can display, including the glow of backlit images.
  • for printing on your home inkjet printer:
    • run a head cleaning cycle then a nozzle check to ensure all nozzles are completely fault free
    • determine the best paper type setting in your printer settings for the paper you intend to use
      • use manufacturer's recommendations, or, if not available,
      • print an ink density chart using different paper type settings and choose the setting which gives you the most distinguishable patches whilst still retaining general print quality, looking particularly at the shadow tones.
    • print the correct size profiling target file supplied by your profile service provider, following their instructions, usually with no colour management selected and printer colour management set to manual and print type to none.
    • mail the print to your profile service provider and they will analyse it and send you back a profile file which you can rename.
  • alternatively you could try a stock ICC profile for your printer/paper.
  • installing and using your new ICC profile:
    • copy it to the correct folder eg. Windows 2000/XP : windows/system32/spool/drivers/color folder
    • restart Photoshop and you can now select that profile and you can then create a soft-proof setup using that profile by selecting 'View→Proof Setup' and also when you print you need to ensure the correct profile is chosen.
  • a profile cannot eliminate metamerism inherent in the inkset - it can however achieve best neutrality under a particular light source while trying to minimise shifts from neutrality under other light sources.
  • the profile represents a best compromise for general reproduction, but may not be the best for certain atypical images such as bright yellow subjects.
  • for example details, see Image Science's profiling service

A comparison of colour calibration kits:

calibration kit: XRite Huey Eye-One Display 2 Eye-One Design Eye-One Photo CV Spyder 2 Suite CV Spyder 2 Pro CV PrintFix Pro Spyder3 Studio      
approx. price (2007 $Aust) $110   $1846 $2599              
monitor profiling Y Y Y Y Y Y N Y      
monitor calibration checking N Y Y Y N? N? N Y      
ambient light measurement   Y Y Y N Y Y? Y      
printer profiling N N Y Y Y* Y* Y Y      
 - scan rows of RGB print colors N N Y# Y N N Y? Y      
 - scan rows of CYMK colors N N Y# Y N N N?        
 - RGB output profiling N N opt Y N N ?        
 - CYMK output profiling N N opt opt N N N        
spot color measurement N N Y Y N N ? Y?      
scan color measurement N N Y Y N N ? Y      
digital camera profiling N N opt opt (SG version) N N ? ?      
digital projector profiling N N opt Y/opt? N N ? Y      
scanner profiling N N opt Y N N ? ?      
MS Windows Vista compatible   N N N Y Y Y Y      

 * Colorvision's Spyder comes with its PrintFix Plus software which only provides profiles for certain printers.

# only via a mini-color patch which is not as accurate as a test of almost 400 colors in the Eye-One Photo version.

photo/colorcalibration.txt · Last modified: 2017/09/16 01:40 by gary1

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