Hype or Hero Take 2: 16 Bit Printers
The digital photography market seems to be heating up with products that boast "groundbreaking" features not found on previous models. Are these groundbreaking products all they are cracked up to be, or are they just hype to get you to buy a new product? Last month we took a look at the potential of full color capture offered by the Sigma SD14 slated for release within the month. This month we take a look at 16 bit printing and the new printers that offer specialized 16 bit print plug-ins. Do they really offer improved color and/or control? What are the benefits and drawbacks? If you wanted to print 16 bits/channel, would you know how to do it in order to get the best results? Let's take a look. Like most things, the answer isn't simple. In the digital world, it can take a little hype to make a hero... or vice versa!
8 versus 16 bits
The most common image format is a format that offers 8 bits per channel. For the typical RGB encoded image, that would mean 8 bits to store the brightness for red, green, and blue for each pixel in an image. Given 8 bits per channel, you get values from 0 to 255 to record the darkest to lightest intensities. Since values of 0 to 255 can be recorded for all three color primaries (red, green, and blue) separately, the total number of colors that can be recorded is 256 * 256 * 256 or about 16.8 million colors. Images that contain 8 bits of information per channel are often referred to as 24 bit images.
A less popular format, but one that is gaining recognition, is the 48 bit image format. This format is similar to the 8 bit/channel format, except 16 bits are used to divide the intensities from dark to light. With this format, you get values from 0 to 65,535 to record the brightness of the primary red, green, and blue colors for each pixel. That equates to 65536 * 65536 * 65536 or approximately 280 trillion colors! All this at a cost of only doubling your storage requirements for each image. Is it worth it? It certainly can be, but let's dig a little deeper and try to discover whether or not printers really need this capability.
The benefits of 16 bits per channel
By far the greatest benefit to 16 bit/channel images and 16 bit/channel processing comes from the initial image capture, particularly when working with digital cameras that must conform to a variety of lighting conditions. Having more "quantization" points in the capture range (65536 versus only 256) allows for finer gradations between each color and allows the photographer to adjust for capture issues like underexposure and even overexposure. Ability to adjust for exposure and still end up with a usable image is very limited when capturing only 8 bits/channel.
Once the initial image capture is done and exposure, white balance, and other factors have been corrected, the performance gap between 8 bit and 16 bit imaging decreases dramatically. Once any initial exposure and white balance issues have been corrected and the image has been developed (from raw format), 8 bits/channel is almost always enough to get you from the developed image to print (or to screen) with no ill effects. I refer to raw processing here because if you record in any other format in-camera: JPEG or TIFF, you'll only be getting 8 bits/channel from the capture image to start with and at that point, the benefits of printing your 8 bit images to a 16 bit printer are almost nil. Obviously the best advice is to shoot in raw capture mode and keep your developed images in 16 bits/channel if you intend to make the most of your 16 bit printer! That's not to say that 16 bit printer drivers can't offer any benefits when printing 8 bit images, but the utility of the 16 bit printer is all but lost if you intend to send it 8 bit/channel images.
16 bits at print time
So the big question is whether or not 16 bits/channel is really needed at print time. All drivers in all Windows operating systems are 8 bits/channel as 16 bits/channel is "foreign" to the Windows operating system. That means that you will always require a special plugin to be able to print 16 bits/channel to your 16 bit printer and the normal "File", "Print" command that you use from your standard photo editor or printing tool will not be able to utilize the 16 bit functionality of the printer.
It is worth pointing out that your monitor will still be running at 8 bits/channel, and you've likely never had any problems with displaying images on your monitor so why worry about the printer? The push behind the new 16 bit printers is the fact that your printer is likely capable of printing some colors outside the range of your monitor's capabilities and due to this extended color gamut, you may need more gradations (bits) to render colors without banding or color posterization.
In reality, there are colors that your monitor can reproduce that are not reproducible by your printer as well. It is generally believed that the human eye can recognize about 10 to 11 million colors. So shouldn't 8 bits be enough since that gives us 16.8 million colors? Like most things, it is a lot more complicated than that, as the 16.8 million colors in 8 bit/channel images are not optimized to match the 10 to 11 million that our eyes see.
"Gamut" simply refers to the range of colors that can be reproduced. Your PC monitor loosely conforms to a color gamut called sRGB. sRGB is a relatively small gamut and due to its size, 8 bits/channel is enough to represent all colors in the sRGB gamut without any noticeable banding between colors. While sRGB is good enough to capture almost all colors that can be rendered by your monitor, your printer can likely reproduce colors outside the sRGB gamut: colors that we can see and the printer can reproduce, but will be "clipped" by the sRGB gamut. If you capture your images in sRGB color space or develop your raw photos into sRGB color space, that means you won't be able to print all possible colors that your printer can reproduce.
Adobe RGB is probably the most popular gamut being used by professionals. It is a larger gamut and can therefore capture a wider range of colors, and it is still small enough that 8 bits/channel is enough bit depth to render smooth color throughout the gamut. Adobe RGB is easily large enough to accommodate your monitor, but your printer will still be able to reproduce some colors that are beyond even Adobe RGB.
When you go beyond Adobe RGB and start using color spaces with very large gamuts (such as ProPhoto RGB or Wide Gamut RGB), the gamut is so large that 8 bits/channel may not be enough and you may start to see banding in smooth but gradually changing colors such as a blue sky just before sunset. Here, 16 bits can help because you have more gradations to work with. To put it simply, spreading 16.8 million colors across a large color gamut may be spreading things too thin and you may end up with noticeable difference between "adjacent" colors and that, in a nutshell, is what causes color banding in areas that should be smooth.
How bad is the problem to start with though? Is Adobe RGB really inadequate to reproduce your photos on your printer? The answer to that question depends on many factors including the colors in the image being printed and the printer you are using. Generally printers with more ink colors produce larger gamuts, so printers like the Canon i9900 and Epson R1800 have larger gamuts just because they have a wider range of ink (colors). Let's take a look at the color gamut of the i9900 on Canon's Photo Paper Pro compared to Adobe RGB:
As you can see, there are many colors in Adobe RGB (represented by the wire frame above) that the i9900 printer (represented by the solid shape) cannot reproduce, but there are some "slivers" of color that the printer can reproduce that Adobe RGB will clip. These problem areas where the color space isn't large enough to hold the color reproducible by the printer are represented by the small sections of solid surface that poke through the wire frame above. The biggest problem area is the swatch of mid-brightness cyan/green on the bottom left above. As you can see by the area of cyan/green that pokes through the Adobe RGB wire frame, there are some cyans and greens that cannot be printed using Adobe RGB. Whether or not this is a problem in your photographs depends on how many photographs you print that happen to have that shade of super-saturated mid-brightness cyan and/or green. But wait. It gets even more complicated. Can your camera even record that information to begin with? We'll get to that in a minute.
The biggest selling point for 16 bit printers/drivers is that you need more bits to support the larger gamut of the printers. Given that the color gamut of the new 16 bit printers isn't really any larger than current 8 bit 8+ ink printers, it doesn't follow that 16 bits would be required to support the full gamut of the printer. In the end, it comes down to selecting a color space that has a gamut big enough to support all printed colors but not so large that it requires 16 bits/channel to cover the gamut "smoothly". Yes, if you shoot in raw mode, convert to the super-large ProPhoto RGB, and keep all your developed images in 16 bits/channel all the way to print, the 16 bit printer/driver may help. Part of the reason it helps, however, is that there's a lot of overkill in that workflow.
At first it might appear that you are losing a good chunk of highly saturated cyan/green colors if you decide to use Adobe RGB for the color space of your developed images, along with a small sliver of magenta and yellow. When we dig a little deeper, however, we find that the color gamut of the camera's image sensor is even more limiting than Adobe RGB on the cyan/green edge. This is the color gamut of a Canon 5D Professional dSLR camera. The color gamut that the camera is capable of recording is the wire frame and the color gamut of the i9900 printer is the solid shape.
Due to the way CMOS and CCD sensors are constructed and the light filters that they use, other cameras like Nikon Professional dSLR cameras have the same limitation on the cyan/blue edge of the gamut, meaning that you gain almost nothing from developing your photos into a super large color space like ProPhoto RGB because your camera cannot capture much more data than Adobe RGB anyway, at least where it is needed!
What all this boils down to is the fact that you need to compare the color capabilities of the camera combined with the reproduction capabilities of the printer itself and when you do that, Adobe RGB is an excellent match and using anything larger is really just overkill. For the purist who is worried about losing a tiny sliver of highly saturated yellow or magenta that will likely go unnoticed in the few photos that actually contain those colors, I have developed a color space slightly larger than Adobe RGB that is designed to cover the entire gamut of today's printers without being excessively large and requiring the jump to 16 bits/channel.
This printer-optimized color space, called pRGB (for "Printer RGB") automatically installs in the Qimage program folder (usually \program files\qimage) when you install Qimage, so give the Qimage demo a try as it may help you with color managed printing anyway, and as a benefit, you automatically get the printer-optimized color space that works well with any 8 bit printer. If you want to use it for your other work (like using it in your raw conversion tool or your photo editor), simply right click on the pRGB.icm file in your Qimage install folder and select "Install". At that point, you can use that color space in any Windows application and you can use it the same way you would any other color space like Adobe RGB, ProPhoto RGB, etc..
Given the fact that 8 bits/channel is enough for finished/developed Adobe RGB images and enough to reproduce almost the entire color range that can be captured by your camera and later reproduced by the printer, I'm going to have to call 16 bit printers/drivers mostly hype at this time, at least given the current state of printing and display technology. Shooting in raw capture mode, correcting exposure/color issues there, developing into 8 bit Adobe RGB or pRGB images, and printing to an 8 bit driver is all anyone, even the most critical professional should need.
What about the reviews of 16 bit printers?
I've seen a handful of reviews on the new 16 bit capable printers and some reviewers do claim to see some differences in the 16 bit versus 8 bit output of the new printers. I've seen some claims of "more vibrant" or "smoother" colors for example. I'm quite skeptical at this point at the notion that these differences are really the result of 16 bit/channel capability! I believe there are a lot of potholes in trying to review these printers. As an example, I asked one professional photographer to send me prints from his Canon iPF5000, one done in 16 bit mode and one in 8 bit mode because he claimed he could see benefits to the 16 bit mode in several more demanding shots. I did see that the 16 bit version looked a little smoother in a few places so I asked him how he printed the two versions. He told me that he started from a raw image, converted to ProPhoto RGB, and then printed. Knowing that ProPhoto RGB can show some banding for 8 bit images, I asked him to go back and convert the original raw image to Adobe RGB and reprint the 8 bit version. The banding was gone. This was simply a case of needing to know how to best utilize both technologies (8 bit and 16 bit) and how to make the most of the 8 bit technology. I wonder if some reviewers may have fallen into the same pothole and come to the same (misleading) conclusion.
I will have to say that the 8 and 16 bit versions still looked a bit "different" with respect to slight color casts and certain colors, but one really didn't look "better" than the other to me. I attribute the minor differences in look/feel to the fact that the 8 bit and 16 bit drivers are two completely different drivers and may handle color just a bit differently. I also have to wonder if slightly different optimizations in the 16/8 bit drivers alone lead to some reviewers giving the 16 bit specialized driver the nod over 8 bits. As a matter of interest, the same raw file when developed into Adobe RGB in 8 bits/channel and then printed to an older Canon i9900 (which is not capable of 16 bit printing) produced a print every bit as good as the iPF5000 print in either 8 or 16 bit mode. While these tests are hardly definitive, at this point, logic has to step in and you have to wonder how we've been using 8 bit/channel printers for decades, profiling them in raw (no color adjustment) mode, using different papers, etc. and have never had a problem. Yes, sometimes it's hard to realize what you were missing until you see the new technology, but I'm not seeing any real benefit to 16 bit printing at the moment. As technology on both ends (camera to printer) improves over time, I may have to revise my outlook in a future article. :-)
I do think 16 bit printers can make workflows easier if you choose to go the overkill route all the way (raw to ProPhoto RGB color space, keeping the 16 bit/channel image format all the way) because you don't really have to worry about being careful. That does have some appeal, but as long as you shoot in raw, do any "heavy handed" manipulation like large changes to exposure and/or white balance at the raw stage before you develop, you can still develop to Adobe RGB, print to the standard 8 bit driver, and get results that are as good as the 16 bit driver plugin on the same printer. One final thought to keep in mind is that storing developed images at 16 bits/channel doesn't just fill up your hard drive faster. It creates added burden at the processing stage as well by doubling the amount of memory needed to process (interpolate, sharpen, spool, etc.) and that can result in problems when doing things like printing very high resolution scans or photo montages or printing large prints. I think that 16 bit printers are new enough that the jury is still out as far as the total benefits offered by 16 bit printing. I would simply caution that changing your entire workflow to 16 bits at this point simply because you own a 16 bit printer may be a bit premature and may lead to unnecessary side effects.
Certainly, we live in a "more is better" world. Just look at how manufacturers are still able to sell consumer level cameras with more pixels and pixel counts continue to increase every year despite increased image noise and a general decline in overall image quality. Right now, with the current state of technology considering cameras, monitors, and printers, I really don't see any real benefit to 16 bit printing over 8 bit printing when 8 bit printing is done properly. That said, it can be easier to foul up 8 bit printing and end up with artifacts like banding and color posterization if heavy editing like exposure correction or white balance is done at the wrong stage or one tries to use a super large color space like ProPhoto RGB in 8 bit mode.
The bottom line is that I believe there will be little or no difference between 8 bit and 16 bit printing provided you follow an acceptable workflow for both. If you've been thinking of shelling out a few thousand dollars on a new printer because it is touting 16 bit printing, my advice is to hold on to your money for a little while longer. As with anything in the digital imaging industry, a general consensus will emerge in the next 6 to 12 months about how useful the 16 bit printing really is, and certainly these new printers (which I'm sure you have noticed will go unnamed in this article just to be "politically correct") have benefits above and beyond just being able to print at 16 bits/channel so as more and more people use them, the benefits and costs will become clear over time. The handful of 16 bit capable printers offered at the time of this writing are excellent printers, just don't buy them solely for their 16 bit print capabilities. In closing, I do believe 16 bit printing capability is a good feature and wouldn't mind seeing it on all printers, but it certainly should be low on the priority list when evaluating what you need in a photographic printer as the real world benefits are quite limited.
-- Mike Chaney