cgardner
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 p.3 #3 · Canon xsi vs 5D resolution | |
Many years in the reproduction game have taught me that the weakest link in the chain is the human eye and brain.
Few if any images are ever viewed at captured resolution. The irony is that as capture resolution in the camera has increased so has the amount of down-sampling required to produce web-viewable image sizes from the original. So all that extra detail which is captured gets resampled away in the resizing process. Sure the 100% crops will look different and better with more sensor resolution, but by the time the two images are re-sampled to 800 x 600 pixels and sharpened normally you will not see enough difference to loose sleep over, or disposable income if you fight the urge to upgrade at every incremental increase in resolution. Capture resolution matters more nowadays if you make large prints.
I've worked in printing related graphic arts since the mid-1970s and had been using Photoshop with high-res scanned images for years at work before deciding in late-2000 to spend my own money on a digital camera. I knew from my experience in offset printing and scanning for printing that output resolution is where the rubber hit the road in reproduction. It really doesn't matter how much detail the camera captures if the eye can't see it in the final reproduction. How much resolution can be achieved in output is a function of the physical limitations of the output medium. Only so many RGB pixels can be crammed into square-inch of a monitor and to get that image each RGB pixel value must be converted back into individual red, green, and blue glowing dots. Only so many hard dots of transparent ink or dye can be put in a square-inch of paper before they spread and mush together. There is a point of diminishing returns with output resolution...
The 300 ppi benchmark for output resolution is a result of the fact that its very difficult to print image on an offset press when the physical dots of solid ink are closer together than 1/150th of an inch or 150 DPI. To create an conventional offset printing dot digitally requires each one to be made up of grid pattern with 0/1, on/off values. Early analog/digital scanners imagesetters used a 6x6 grid and 8x8 grid was used for early laser printers resulting in dots with 36 and 64 discrete tonal values respectively. With experimentation it was found that a range of down-sampling rates from image pixels to printing dots of between 1.7:1 to 2:1 would produce an image the human eye would accept as continuous tone at normal reading distances: 240 - 300 ppi for printing with a 150 DPI line screen.
So back in the late 1990s when deciding when to jump from film to digital cameras I just did the math at the benchmark 300 ppi output resolution to reveal what camera resolution would be needed to create various standard size print images without resampling:
4x6 = 1200x1800 = 2.16 MP
5x7 = 1500x2100 = 3.15 MP
8x10 = 2400 x 3000 = 7.2 MP
11x14 = 3300 x 4200 = 13.9 MP
12x18 = 3600 x 5400 = 19.4 MP
16x20 = 4800 x 6000 = 28.8
So I pretty much had planned my life-long upgrade strategy before every buying my first digital. With a drum scanner and $24,000 24-inch wide Rainbow dye-sub proofer available I really didn't have a compelling need to buy the first one, but like any geek I just wanted one. But I'm also frugal and passed on the $3,000 3.0 MP D30, and bought a $500 2.1 MP Kodak DC290 instead.
One of the reasons I didn't make the jump to DSLR immediately was because I was a Nikon film body user (NikonosII, F, Nikonos V, N8008) but saw that the CMOS used in Canon was superior in most respects to CCD technology which I was very familiar with from scanning experince. Another was buying an Pextax WR90 film P&S for a trip in 1997 and discovering that in 80% of the situations I shot at the time it did as good or better than my SLR, albeit without as much creative control. But I'm a sucker for convenience....
I knew that 2.1 MP was enough resolution for acceptable looking screen images at 72ppi and for making a decent looking 4 x 6 print without re-sampling and degrading captured detail, and make a pretty decent looking 5 x 7 with moderate up-sampling or a reduction in output resolution, two means to the same end. I picked the 2.1 MP DC290 over other similar priced 3.0 MP P&S models because it had a lens / sensor combination which produced images with better color saturation, contrast and lens CA. For most early P&S cameras it was the lens CA that spoiled IQ, not the difference in the sensor resolution.
I did a lot of experimentation with that little camera, printing the same photo in 8x10, 16x20, and 24x30 sizes by either using the original camera file and changing the output resolution, or up-sampling in Photoshop to increase he actual physical file size to allow output at 300ppi. Genuine Fractals arrived about that time is I experimented with it as well. I found that with a bit of compensation with sharpening I could produce a pleasing 24 x 30 image from that 2.1MP image, if viewed at a distance. It didn't look as good at reading distance, but that points out another important perceptual variable: viewing conditions. How much resolution is needed in image to make it appear acceptable is inversely proportional to the viewing distance, and the amount of sharpening needed is proportional with size and viewing distance. That's something impressionistic painters discovered in the mid-1800s.
One of my favorite painters is John Singer Sargent who painted larger than life portraits which have exquisite detail and contrast - when viewed from across the room. I'm fortunate to live near DC and the National Portrait Gallery where several of his more well known works are displayed and when examined close-up I discovered the paint was literally trowelled-on with a pallete knife. LIke USM in a photograph he created the illusion of sharp detail with the use of contrasting tone.
So my point here, is that how an image is output and viewed has far more bearing on PERCEPTIONAL image quality than how the pixels look at 100% on your monitor. Depending on what you plan to do with your images a 3, 5, or 8 MP camera may be all the resolution you really need...
I went from the DC290 to a 5MP Minolta D7Hi in late 2001 more for the creative controls and the nice sharp, relatively CA free 28-200mm equivalent lens. Its still my walk-about camera of choice. I finally made the jump to Canon DSLR in 2004 after getting a set of studio lights and finding the Minolta very limiting in terms of aperture and DOF control (due to the small sensor) and image noise. The 20D was one of the first cameras with Digic II and E-TTLII which resulted in significant improvement in TTL flash metering, an important consideration for me. It also arrived at market with the 10-22mm EF-S lens which addressed the lack of extreme wide angle capability in the 1.6 crop format. All things considered I'd have preferred a 5D at the time but didn't want to spend almost 3X more for it.
With the 20D I can produce an 8x10 print @ 300 ppi output with only minor up-sampling (native size at 300ppi is 11.68 x 7.79). I rarely print larger and when I do I know how to compensate in other technical ways such as contrast and sharpening for maximum perceptual image quality at the typical viewing distance. In other words I'm experienced enough to know that the photo on the wall over the couch does need to have the same resolution as an print at normal reading distance.
It's a terrible dilemma for a geek to know rationally there is really no compelling reason to upgrade for higher resolution. More than once I've come close to pushing the "confirm purchase" button on a 5D or a 40D before the frugal genes kicked in and froze the finger in mid-air. I've purchased and used an XT at work and didn't notice any huge difference vs my 20D in the final images and didn't like the ergonomics of the smaller size.
The thing that will finally compel me to upgrade from the 20D will be improved AF performance (not Canon's forte lately) and the 14-bit tonal range. Since I never upgraded to digital for video the HD video capability of the 5DmkII is very attractive, but I know if I wait for the 60D it will likely also have that feature and I'll be able to keep using my beloved 10-22mm EF-S instead of needing to also buy a 17-40mm for a 5DmkII.
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