In an earlier post on my printing workflow, I mentioned using the ProPhoto RGB color space for editing (“working color space”) and the reasons behind that choice. This post explores this topic further, looking closer at the gamuts of photos and modern output devices and how they relate to sRGB, Adobe RGB and ProPhoto RGB. Those are the three most commonly used working color spaces for image editing, i.e. color spaces in which image data is stored and edited. The case for using ProPhoto RGB instead of either of the other two is based on three facts:
- Modern wide-gamut monitors have a gamut that exceeds sRGB and AdobeRGB in some areas.
- Modern inkjet printers also have a gamut that exceeds sRGB and AdobeRGB in some areas..
- There are real-world photos whose colors are outside of sRGB’s and Adobe RGB’s gamut.
In the following sections, we will look at each of these point in detail and in the end also try to come to some judgment on how much impact the choice of ProPhoto RGB versus a smaller color space has in practical results. As a side-note we will also talk about the importance of using higher color depth with larger color spaces such as ProPhoto RGB.
Color Space Visualization
To visualize the gamut of color spaces, they are usually displayed in relation to either the CIEXYZ, CIELUV, and CIELAB color spaces. While many articles on the web still use CIEXYZ (originally defined in 1931) diagrams, it is not ideal for comparisons, since it lacks perceptual uniformity and thus may exaggerate differences between gamuts. This issue was solved in 1976 with the CIELUV and CIELAB color spaces and differences in gamuts shown in the CIELUV and CIELAB diagrams better reflect how strong we would perceive these differences. For the remainder of this article we will use mostly CIELUV diagrams, since CIELUV generally does a better job in presenting differences in 2D diagrams, while with CIELAB many of the commonly observed differences hide in the third dimension. Still, also with CIELUV we will in some cases also show 3D diagrams to make certain points.
The pale round shape in the background of the CIELUV and CIEXYZ diagram shows the area of color visible to the human eye. While Adobe RGB and sRGB stay within that area, ProPhoto RGB actually also encompasses areas not visible to the human eye. The CIELAB diagram per definition does not show colors outside of that area, it cuts of ProPhoto RGB flat at the sides where it would protrude into non-visible areas.
If you want to do your own visualizations and analysis, I can recommend the following software. Diagrams in this article have been created with Color Think.
- ICCView: free and simple online tool for comparing two ICC profiles in a 3D CIELAB diagram.
- PerfX 3D Gamut Viewer: free and simple application for comparing up to four ICC profiles in a 3D CIELAB diagram.
- GamutVision: free and quite advanced application for analyzing the transformations between color spaces. So, opposed to the two aforementioned tools, GamutVision focuses on visualization of how image data in one color space would transform into another, using the available rendering intents. It can use built-in sample patterns or you can use your own images for analysis, e.g. to check how a certain image could be transformed to your printers color space. Among others, GamutVision provides 3D and 2D CIELAB diagrams, 2D CIEXYZ diagrams and 2D CIELUV diagrams.
- Color Think: advanced and not-free application to analyze and compare color spaces. It supports 2D and 3D views in CIELAB, CIELUV and CIEXYZ, and can generally compare color spaces (like ICCView or PerfX) and also analyse specific images (like GamutVision).
Wide-gamut monitors with a gamut larger than sRGB are already quite common. While even high-end devices cover only ~ 99% of Adobe RGB, they also exceed it in some areas. Here is an example showing the gamut of my Eizo CG277, calibrated to a white point of 5000K and brightness of 80 cd/sqm.
The first diagram below highlights those areas where the monitor’s gamut exceeds Adobe RGB, the second adds sRGB to the comparison. While Adobe RGB is very slightly larger on the left side, where the saturated greens turn into cyan and blue, on the right lower side, where the blue turns into purple and red, the monitor has a notably larger gamut than Adobe RGB. Only ProPhoto RGB fully covers all colors the monitor can display. As mentioned before, since color spaces are three-dimensional, the 2D diagrams cannot tell the full story. The last diagram below in 3D shows a comparison between the Eizo’s gamut and Adobe RGB, revealing that also in the lightness component there are some areas where the monitor’s gamut exceeds Adobe RGB.
Current inkjet printers also exceed Adobe RGB and sRGB in some areas, for example Canon’s PRO series with the Lucia PRO inks or Epson’s SureColor with the UltraChrome HD inks. Such technology and quality is easily accessible, it is offered by many print shops and A3+ and A2 printers for home starting from 600 Euro.
For this comparison we will show color profiles provided by the paper manufacturer Hahnemühle for their FineArt Baryta paper and the Canon PRO-1000 and Epson SC-P800 printers. The first diagram highlights areas where the Canon exceeds Adobe RGB, the second adds sRGB to the comparison. Clearly the Canon’s gamut exceeds Adobe RGB, especially in the cyan, purple and reds but also slightly in the yellows. The Epson has a very similar gamut to the Canon, which is shown on the third diagram. In case of the printers, the 2D diagrams already tell most of the story. In the final diagram below in 3D you can see that there is only a very small area where the printer’s gamut exceeds Adobe RGB in the lightness component. For the Epson, the diagram would look very similar, so we’ll omit it.
Monitor and Printer Comparison
One argument sometimes heard in regards to using ProPhoto for printing is, that even if the printer exceeds Adobe RGB and sRGB, those colors cannot be shown on monitors and are thus difficult to work with. To look at this a bit closer, the diagram below shows a comparison of the gamuts of the Canon PRO-1000 and Eizo CG277 in relation to Adobe RGB. In the purples and reds it shows clearly that the areas where the Canon exceeds Adobe RGB can still be displayed on the monitor, while in the greens and cyans you’d be “flying blind”. In the yellows both devices extend beyond Adobe RGB, with the printer going a bit further.
In any case, for me personally “flying blind” is not a big issue. Even under perfect circumstances, the monitor will never show the same thing as the print and this is something anyone making prints has to deal with, regardless of gamuts and color spaces.
After all this rather theoretical comparisons, the question looms whether this matters in the context of real-world photographs. To analyze that, here a comparison between a few color photos from my portfolio.
First here are the photos I have analyzed. The two portraits are from a Canon 5D Mark III, the four other photos from a Canon 30D. All photos have been imported to Lightroom and edited according to my preference at that time (no special editing for this analysis). Lightroom internally uses a working color space similar to ProPhoto, and thus editing in Lightroom can easily lead to having colors outside of sRGB and Adobe RGB.
The main argument for retaining those colors outside of sRGB and Adobe RGB would be printing, since presentation on the Web still largely relies on sRGB anyway. So, the following following diagrams show the colors of those photos in relation to the Canon profile and Adobe RGB. The first diagram merges all photos together. The second does the same, highlighting those areas where the printer profile exceeds Adobe RGB, thus pointing out where the printer can make good use of the colors that only the larger, ProPhoto-like color space can manage. The subsequent diagrams show the same diagram for each individual photo.
You can see that even the portraits with very muted colors exceed Adobe RGB significantly in some areas. However, when focusing on those areas where that excess can still be printed, you’ll see that the areas where the printer exceeds Adobe RGB the most (the green, cyan, blue and purple edges) are not used very extensively. The most notable area are the reds, where in the second-to-last photo there are a lot of tones falling in the area that exceeds Adobe RGB but is still printable. Also the oranges and yellows are heavily used, but here the advantage of the printer over Adobe RGB is not so significant. Of course this analysis is also based on my own choice of color photos - there may well be other photos out there that will paint a different story and for example use the cyans more excessively.
However, even for those colors that exceed both Adobe RGB and the printer’s gamut, having the color information available in ProPhoto RGB (and 16 bit) is advantageous: for the perceptual rendering intent, there is more and better information available to retain fine gradients instead of clipped colors when transforming into the printer’s gamut.
What I cannot show you here is the comparison in print. I printed some of those photos, in each case one copy via Adobe RGB and another via ProPhoto, all via the printer profile shown here with the PRO-1000 printer on Hahnemühle’s FineArt Baryta paper. My impression is that the differences are visible when putting the two copies next to each other under good light. However, if looking at the print via Adobe RGB alone, I would not say that anything is amiss or the print is of inferior quality.
ProPhoto RGB and Color Depth
And now a final note on color depth: you may have noticed that above I have mentioned storing data in 16 bit. When using a larger color space like ProPhoto RGB, then having a greater color depth is more important than for smaller color spaces to support smooth gradients and to avoid banding. Thus I would always recommend using ProPhoto RGB together with 16 bit color depth instead of 8 bit. As long as you keep your files in RAW and work with a tool such as Lightroom, this has no real impact on your storage, but if you store files in TIFF or PSD format in 16 bit, they will take more space. If storage costs are an issue for you, this is of course a factor to think about.
Based on this analysis, I stand by the previous recommendation of ProPhoto RGB as working color space for a workflow that goes beyond presentation of photos on the Web and into high-end printing. Summarized the reasons are:
- Current wide-gamut monitors and high-end printers all exceed Adobe RGB by some margin and sRGB significantly.
- This excess is actually relevant in real-world photos.
- Future development of monitors and printers will only widen those margins.
- A workflow in ProPhoto RGB (and 16 bit) retains color information and fine gradients, and gives you the best material to work with when in the end having to fit your photo into a smaller color space, like that of a printer.
Of course especially when compared to Adobe RGB the significance of ProPhoto RGB’s advantages is up for debate. However, with enthusiasts investing in the latest and greatest full-frame cameras and expensive lenses to maximize image quality, and high-end printers also being relatively accessible, I do not see why you would want to limit your workflow on the software side with a smaller working color space.
I hope that you found this article interesting and helpful! As always I am happy to hear your comments, you can contact me here.
All the best, Robert