Even when the megapixel count gets to the point where it matches film, there are still a few more issues on quality that you need to be aware of. These issues stretch beyond the megapixel problems, and reach both aesthetic value and bottom line results.
The first problem (and the most obvious) are digital artifacts which show up in images, such as "pixelation". Pixelation refers to being able to see the pixels, which is a dead giveaway that the image is digital. More importantly, if you can see pixelation in the photo, it generally detracts significantly from the image. Pixelation generally occurs from two sources; if you enlarge a digital file beyond it's limits (trying to make an 8x10 print from a 1 megapixel file) or if you increase the sensitivity of your digital camera when taking a photo (increasing the sensitivity can add "noise", which often creates an obvious pixelated look in the final prints, generally in the blacks or shadow details). Because the sensors use specialized masks to accurately read color, you can also get moire patterns and other unwanted artificats in digital images. Processing software in the digital camera and compression of image files can also degrade quality and add unwanted artifacts. These problems are unique to digital photography, and are in addition to the standard lens problems such as chromatic abberation.
Another significant issue that bothers me more than most is the lack of optical quality in most digital cameras. Currently, very few manufacturers pay attention to the optical quality of their lenses. Why? Most digital cameras are not yet capable of showing the difference between a good lens and a junk lens (megapixel resolution isn't high enough yet, except on top cameras). Another major reason? Manufacturers know that they can get away with it, paricularly if they do it to drop the price of the camera while offering higher megapixels. A bad attitude if you ask me, particularly since I don't want to spend extra time editing color balance or abberations in Photoshop just to correct the manufacturer's laziness in lens design. Popular Photography noted this issue in their Feb. 2003 article on how many megapixels you need, saying that a high quality 2 or 3 MP camera can provide better results than an inexpensive 4 MP model that uses a poor lens.
Some manufacturers are beginning to address this issue, but not fully. Sony offers models with a 10x Zeiss design lens, and Panasonic recently launched a series of cameras with Leica designed lenses. However, you need to keep in mind that while a 10x Zeiss lens may be of reasonable quality, it's still a 10x zoom, and you just can't get the highest quality results from a 10x lens. At $1500, the 35-350L for the Canon Eos line is regarded as a mediocre lens for critical purposes, and has significant distortion through the range (where the lines bend rather than remain perfectly straight, as in a good fixed lens). If $1500 is the cost for a reasonable quality (but not great) 10x optical zoom, you had better believe that the big optical zooms found on digital cameras that cost significantly less don't offer anywhere near the same optical mark, even if designed by Zeiss. Likewise, the lenses on most digital cameras only match a point and shoot lens at best, and certainly not a good quality lens on an SLR. This is a solvable issue, but will not improve until digital photographers start demanding high quality lenses on their digital cameras as they do for their film cameras. Until then, keep in mind that the lenses on most digital cameras are not the best in color rendition, sharpness, or overall resolution.
Also keep in mind that "digital zoom" features are not particularly helpful. These features crop your image to give a magnified view, which as any photographer can tell you, cuts down image quality. The true use of a digital zoom feature is to help view an image on the camera's tiny screen, but as a feature for "zooming in", it does very little. Unfortunately, a number of salepeople use the digital zoom as a big selling point, but it does not help in zooming your actual image and does not let you zoom in and keep full image quality as they may imply.
Lee Craker, a photographer who does a good deal of digital work, brought two other issues to my attention. First, consumer digital cameras and film scanners can not yet capture shadow detail or the dynamic range of film. (Professional cameras, such as the EOS-1Ds, now offer chips that offer better color accuracy and range than film, but these chips are still in the $5000+ professional models and it will take some time for the technology to get down to the consumer cameras.) This can be a significant factor in prints, particularly of large size. A digital print may look good, but the film counterpart will have better highlight and shadow detail. Second, there are no "film types" in digital photography. In film, every emulsion reacts a little differently and offers a distinctive look. Some photographers insist on a particular film, like Fuji Reala or Kodak 100VS, because they like the way it looks. Digital does not offer the option to give you a specific "look" as you do with film. To get the same effect in digital, you would have to spend a lot of time balancing the color and messing with image until you get the effect you want - time consuming and difficult.
Finally, keep in mind that most digital cameras do not offer very many manual overrides. They are basically point and shoot cameras, and do not allow you to have much control. For most images, this may not be an issue. But if you want to control depth of field, you will not be able to do so unless you buy a high end camera. Exposure compensation and other standard manual controls found on SLR cameras are likewise missing unless you get a high end digital. The lack of such controls will not affect the resolution of an image, but can hinder creative efforts or attempts to correct exposure. So if you are looking for a digital for serious photography, be sure to select a model offering reasonable override capabilities.
That, in a 6 part nutshell, is the dark side of digital. To say the least, digital is a more complex issue than the notion of "point, click, download" everyone has been bombarded with. Film, in its own way, can be just as problematic (or more so in certain situations), but film issues are generally well documented where digital issues are not. While the previous sections may seem an indictment against digital, it is important to understand that digital will be the future of photography, and you can do extraordinary things even with "outdated" equipment from a few years ago. Explore the present and future of digital in the next section:
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