PIA Color Management Conference - Advanced RGB Workflows
Perennial conference favorite Don Hutcheson of Hutchcolor, LLC again presented his thoughts on the values of RGB workflows at the PIA Color Management Conference held last month at the Hotel Valley Ho in Scottsdale, Ariz.
His presentation was broken out into two different sessions — one to cover basics and another for advanced concepts. In the Advanced RGB Workflow session, he began by talking about the different RGB working spaces. He said that the RGB color space you use should have a color gamut equal to or greater than your output device (press) and your input device (camera or scanner). Converting into too small a color space causes clipping.
Don reviewed all the most frequently used RGB color spaces:
- Smallest space
- Best for Web only images
- Bad space for photo editing
- Best safe, general-purpose working space
ProPhoto RGB (below)
- Larger space, but parts of Pro Photo RGB (greens and blues) have illegal RGB values
The image above shows the ProPhoto RGB color space and how colors in the deep blues and greens are outside the CIE color space - beyond the limits of human color vision (illegal RGB values).
- Don't use it unless you REALLY know what you're doing
- Similar to his own DonRGB.
Xtreme 16 RGB (below)
Extremely large RGB space
- The largest possible Photoshop-legal tricoordinate RGB space.
- Must use 16 bit images only
- Contains a lot of illegal RGB values
- Bad space for photo editing
- Extremely large RGB space
You can see from the graphic above just how crazy large the Xtreme16 RGB color space is. In his typical humorous fashion, Don added that viewing XtremeRGB images may cause hallucinations or eye cancer (i'll take his word for it).
He went on to discuss Matrix vs 3D table based display profiles and how they work when viewing out-of-gamut RGB color. If you want to see beyond the monitor gamut, you should create a table based monitor profile. Printer-like gamut compression will approximate out-of-gamut colors.
Don showed his RGBXplorer8 image (shown above) which is used to check any source or destination profile for reversals, hue shifts etc. Limitations of table based profiles are that saturation areas may appear weaker; they are not recommended for soft proofing.
Don then covered soft proofing in Photoshop as he went through the Proof Setup options. He illustrated how, when soft proofing in Photoshop, you should use a white color around the image instead of black, because with a white background any changes in color balance and lightness are obvious. A black background makes it difficult to judge color balance and lightness in an image. Don has a free action (DonzRGBactions) that adds a temporary white border around an image on his website (www.hutchcolor.com).
Don on Bit Depth: Use 16 bits when importing RAW camera data or editing in wide gamut space like Pro Photo RGB. He showed an example of editing a dramatically underexposed 14 bit image in 16 vs 8 bits. The image edited in 8 bits showed obvious signs of color breaking and posterization in dark shadow areas.
For images destined for Web
- Convert all images to sRGB
For images destined for offset print
- Embed the working profile
- Optionally convert to Adobe RGB for safety
For images destined for Wide Gamut (ink jet)
- Embed the wide gamut working space
- Set RIP to recognize embedded profiles
Safe standby: PDF X-1a
- Convert all colors to CMYK output space.
- Can't repurpose wide gamut data.
Most RGB-flexible: PDF X-4
- Allows multiple color spaces
- Not compatible with older RIPs
- Requires very careful set up and testing
When it is better to work in CMYK
- When you have solid vector elements
- When you have colored headline text
- Small edits to a legacy CMYK file
When you have uncertain recipients
- May not understand RGB files or embedded profiles
- Non-automated custom or hybrid CMYK conversions
When converting RGB to CMYK in Photoshop it is always important to go to: Edit - Convert to Profile and choose the proper Destination profile and Rendering Intent as shown in the image above. Never use Image - Mode to convert an RGB file to CMYK.
In-RIP conversion to CMYK:
- OK, but you must test it first
Most RIPs don't offer the ideal rendering intent -
- Relative colormetric with Black Point Compensation
- Avoid Postscript conversions at all costs
Don added a few important thoughts on CMYK profiles:
- Avoid custom press profiles if possible
Use generic GRACoL2006 or SWOP2006 for normal work
- GRACoL2006_Coated 1v2.icc
- Both profiles along with SWOP Coated5 are free at www.idealliance.org
- Only make a custom press profile if your process is not typical commercial or publication offset
The three images above illustrate how having just one bad target patch during the process of creating a custom ICC output profile can cause problems. Here, one skin tone-colored patch is off. And the resulting image converted with the custom profile shows a young woman with bad, posterized make up job.
He then discussed the concept of controlling the black channel in an RGB workflow with proper use of GCR (Gray Component Replacement)... Black is the most visible dot on press - not wanted in skin tones, so keep them off these areas. But maximize black in saturated colors - CMY inks reduce chroma, while black ink increases chroma.
To prove his point on why it's important to maximize black in saturated colors, Don showed his audience the color chart shown above which has two saturated red patches made with identical component colors (100M, 100Y) but each made up of different dirty colors - one with 0C and 80K and the other with 80C and 0K. You can see that the red patch made with 80% black is much deeper and richer than the patch made up of 80% cyan.
Customized GCR trick - Don showed a technique whereby you convert an RGB image twice - through both high and low GCR profiles. Paste the image with high GCR separation over the image containing a low GCR spraration as a layer and restrict areas with a mask. It's a quick way to give you a customized image with optimized GCR.
The image above shows how you can select the Intelligent Black box which allows you to control the black generation when making a custom profile in Xrite's i1Profiler software. The settings on the left would create a light, skeletal black, while the settings on the right would create more of a full-range black.
Don wrapped up his presentation by summarizing his list of safe RGB editing rules in prepress production:
Stay in RGB as long as possible
- But soft proof RGB in CMYK (Command-y)
- Stay in 16 bits as long as possible
Keep edits in Adjustment Layers
- Don't flatten the layers unless absolutely necessary
- Only judge color on a calibrated, profiled monitor
- Embed the profile when saving
All images used with permission of Don Hutcheson - Hutchcolor, LLC - www.hutchcolor.com