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Archive for 2007

2007.11.26

Dust is everywhere. As you know, DSLR cameras occasionally get dust on their sensors which is why most modern DSLRs feature shaking sensors or low-pass filters to reduce dust accumulation. Lenses, on the other hand, get dusty far more often then imaging sensors. They even get dusty while waiting to be used because the lens caps are not dust-proof. Several companies make dust-proof and weather-proof lenses which prevent dust and moisture from entering the interior of the camera and lens. However, they still let dust slowly seep through their lens cap. It is time someone made dust-proof lens caps! Make it reasonably priced and I’ll buy one for each of my lenses.

2007.11.06

Every once in a while, it is fun to compare completely different things just to see where they are relative to each other. Among digital cameras, we have the ultra-compact models on one end of the spectrum and the digital SLRs on at the opposite end. For former are designed to provide good-enough image quality in the smallest package possible, the latter as designed to be uncompromising and produce the best image quality.

Technologically, DSLR cameras have a serious advantage over much smaller camera: Size. Specifically, the size of their image-sensors. Larger image sensors have an advantage because of their greater surface area which can gather more light. Considering image quality alone, no matter what we can obtain with a small sensor, we can also go better with a larger one. Basically, whatever technology exists to make the best sensor for an ultra-compact, the same technology could be used to make a sensor for a DSLR. If the number of pixels remains unchanged, the DSLR will have larger pixels and therefore its images which show less noise and greater dynamic range. Well, I’m over-simplifying a little, but not by much.


So here we go again, we have another silly pointless comparison between one of the latest ultra-compact digital cameras and one of the latest DSLR cameras. For those who missed it, we did this before in the full review of the Fuji Finepix F30. As we saw in that comparison, the F30 turned in quite an impressive performance if we ignore the sharpening artifacts. Here are unmodified 100% crops of matching ISO of the Fuji Finepix F50SE and the Sony Alpha A700. Results are discussed below.

Fuji Finepix F50SE Sony Alpha A700
Fuji F50 - ISO 100 - Crop 100% Sony A700 - ISO 100 - Crop 100%
ISO 100
Fuji F50 - ISO 400 - Crop 100% Sony A700 - ISO 400 - Crop 100%
ISO 400
Fuji F50 - ISO 1600 - Crop 100% Sony A700 - ISO 1600 - Crop 100%
ISO 1600

It is easy to see that the colors are not the same between the two cameras. Both were set on automatic white-balance, both on auto-exposure, taking pictures of the same scene under the same lights. Neither of them reproduced the true colors, but the Fuji Finepix F50SE did much better. For reasons I do not understand yet, DSLRs get the white-balance of incandescent lights more wrong. Perhaps fixed-lens cameras can read more sample-points when computing white-balance because they can read any point of the sensor, while DSLRs have to rely on a dedicated sensor which provides less sample points. Note to self: investigate this further.

In this comparison, the advantage of the ultra-compact seems to stop at better white-balance. Even at ISO 100, the Alpha shows a slightly sharper and smoother image. Although it cannot be seen in these crops, this scene has more contrast then either sensor can capture. The rendition of overall tonalities favor greatly the DSLR which clipped less highlights.

At higher ISO, the DSLR leaves the ultra-compact in the dust. Noise levels increase much more rapidly with the F50 than with the A700. Although both cameras keep a relatively good amount of sharpness across ISO, the Sony Alpha A700 still produces a usable ISO 1600 while the F50’s equivalent crop is a mess.

[eminimall]

The final word is that current digital SLRs produce images with much less noise and better sharpness when equipped with a good lens than ultra-compact cameras. Not only that, this image quality gap has apparently increased in the last few years. This can only be explained by the rapid expansion in resolution among fixed-lens cameras. Do not forget that differences between DSLR cameras and ultra-compacts are numerous, image quality is just one of them.

Neocamera Blog Neocamera.com © Cybernium.

2007.11.04

Sony Alpha A700The Sony Alpha A700 now has a full-review posted at Neocamera. This is the first of a new generation of 12 megapixels cropped-sensor DSLR cameras. Already for this one the results in terms of performance and image quality are good. Nikon will follow soon with its D300 aimed at even more advanced users. Pentax is expected to make an announcement shortly, presumably using the same Sony sensor as the Sony A700 and Nikon D300.

Interestingly, roughly 3 years ago, Nikon announced the D2X, the first 12 megapixels cropped-sensor DSLR. It retailed for just under $5000 USD and supported ISO sensitivities up to 800. Just under a year and a half ago, Nikon refreshed that model with the D2Xs that kept the same sensor and 5 FPS full-resolution continuous shooting but added an 8 FPS 6.8 megapixels cropped drive. Today, the Sony Alpha A700 sells for under $1500 and has ISO sensitivities up to 6400. That’s how technology progresses. Its fun to imaging what will we have in three more years.

Neocamera Blog Neocamera.com © Cybernium.

2007.10.28

In our last post, we discussed the difference between noise and noise-density. Basically, noise-density is noise relative to resolution. Output quality, on a particular medium, is more related to noise-density than to noise because most mediums have an optimal resolution. For example, a typical computer display running at 1600×1200, needs about 2 megapixels. More pixels are simply wasted. The quality of an image seen at 1600×1200 is therefore related to the amount of noise that appears at 2 megapixels.

To illustrate the difference, I shot the same scene at 3, 6 and 12 megapixels using the Fuji Finepix F50SE. The experiment was repeated for various ISO sensitivities. The difference is striking: As the resolution decreases, noise decreases in proportion. What is a very noisy ISO 1600 image at 12 megapixels, becomes much less noisy at 3 megapixels. At ISO 400, the crop is noise at 12 megapixels but rather clean at 3 megapixels.

ISO 400
ISO 400 - 12 MP - Fuji F50SE ISO 400 - 6 MP - Fuji F50SE
ISO 400 - 3 MP - Fuji F50SE

All these images come from the same camera yet they show very different noise characteristics. The only difference is resolution. The top left image was shot at 12 megapixels, the top-right at 6 megapixels and the left image at 3 megapixels.

For an ultra-compact digital camera with a tiny sensor, the performance at 6 megapixels is excellent. At 12 megapixels, it does not seem so great, although it would take a relatively large print to take advantage of all those pixels. When using a medium that requires a resolution lower than that of the image, pixels are down-sampled to the optimal resolution anyways.

ISO 1600
ISO 1600 - 12 MP - Fuji F50SE ISO 1600 - 6 MP - Fuji F50SE
ISO 1600 - 3 MP - Fuji F50SE

Here is the same setup except at ISO 1600 rather than 400. While the 12 megapixels crop shows strong image noise, the 6 megapixels crop is good for an ultra-compact. Indeed, other than previous F-series Finepix cameras, no ultra-compact digital camera can produce 6 megapixels images that are this clean. At 3 megapixels, which is sufficient for 8″x6″ prints, only a little noise remains visible.

Note that these tests were made with the camera set to the desired resolution but nothing prevents users from taking their images at full-resolution in the camera and reducing the resolution later. Actually, this method is generally preferable because you can effectively reduce the resolution in software but not vice-versa. There are advantages though to reducing the resolution of images in-camera: reduced memory requirement and increased speed of operation.

Neocamera Blog Neocamera.com © Cybernium.

2007.10.23

Fuji Finepix F50 SampleMegapixels are increasing. Ultra-compacts such as the just-reviewed Fuji Finepix F50 now sport 12 megapixels sensors. Some people love it, some don’t. The controversy is mostly about image noise. More megapixels generally means more image noise, right? Well, it depends how you see it.

What we have to think about is our medium. How do we look at – not analyze – our pictures? How do we share them? For digital pictures, there are 3 common answers:

  • Upload them to an online gallery.
  • View them full-screen in a slide-show or screen saver.
  • Print them. 4″x6″ is still very popular. Up to 9″x12″ is common now.

If we think about these different mediums and ask ourselves how many megapixels are needed, the answer is less than what most modern cameras offer. For on-screen viewing, the most megapixels of any screen still in-production is 4 megapixels. And that would be for a 30″ LCD such as the HP LP3065. The typical monitor has less than 2 megapixels and so does 1080p HDTV. Prints are more demanding, but even a 300dpi 12″x9″ print only uses 9 megapixels.

So if we have a camera with too many megapixels, what happens to the megapixels we do not need? They do not simply get discarded, they get filtered. The difference? Discarding pixels is skipping pixels and making an image with the rest. Filtering is producing new pixels from a greater number of original pixels.

By filtering, we are affecting the noise-characteristics of an image. When an image is filtered to produce an image with less megapixels, noise decreases. The reasons can be explained by signal processing, but the details are not important for this discussion.

Consequently, the amount of noise a camera produces is not the same as the amount of noise appearing in our prints or on our screens. These noise levels are related, but they are different. Obviously, we want to judge a camera’s image quality based on our medium since that is our ultimate use for images. To this effect, we should not measure noise itself but something like noise-per-megapixel. Lets call this noise-density.


Noise is what we see when view an part of an image on our monitors because we called the image to 100%. Noise-density is what we see when view a photograph in our medium of choice. For large prints, noise and noise-density can be the same, but, for most prints and on-screen viewing, the former higher than the latter. Between a 12 megapixels image and a 4″x6″ print, the difference can be quite striking.

The conclusion from all this is that a camera should be judged on the quality of its output in the medium we use, not by 100% viewing. Viewing at 100% is informative and interesting, but alone it cannot determine wether one camera’s output is better than another. To judge which of two cameras produces better output, they have to be compared using the same medium. That means the same print sizes and the same screen resolution.

For the Fuji Finepix F50’s review, there was a hesitation on wether to give it a Good or an Excellent rating because its image noise is higher than that of its predecessors. However, after seeing that the quality of its prints were so good, the decision became clear: the F50 could not be punished for having that many megapixels if it ended up producing prints that were comparable in quality to other cameras rated Excellent.

Neocamera Blog Neocamera.com © Cybernium.

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