By definition, JPEG is a lossy compression scheme, meaning it decreases the file size by throwing away the data. This is as opposed to lossless compression schemes such as ZIP, which typically do something like reducing redundantly repeated data to shrink the file size. Because JPEG is going to throw away data whenever you save, it *will* decrease in quality (as measured by pixel value differences from the original). You’ve noticed in your own tests, since the brightness values in your subsequent images have changed from the original.

For the most part, however, image degradation at Photoshop’s JPEG 12 setting is negligible – you could save over an image 20 times and you will still have something that more or less matches the original, certainly to the naked eye (as opposed to mathematically calculating the differences).

Eric Westling
Houston, TX
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1) “A TIME-BASED CMOS IMAGE SENSOR,” Qiang Luo John G. Harris
http://www.cnel.ufl.edu/hybrid/_private/publications/tcmosimager_01329135.pdf

2) “A time-to-first spike CMOS image sensor with coarse temporal sampling,” Qiang Luo, John G. Harris and Zhiliang J. Chen

3) US Patent 6069377

=Matt=

And of course, either way it’s DEFINITELY gonna hafta be tripod-only for the type of work I do at f/8 with a polarizer etc, where my average shutter speed is a 1/10 or 10″ even in half-decent light…

I’m sure the main problem will be in designing the circuitry for a sensor that has individually sensitive pixels. Having a different “shutter speed” for each pixel individually could be a monumental programming task…

The closest thing, and an indicator that you may be on the right track, is a sensor like Fuji’s legendary DSLR sensor, with completely different types of pixels on the same sensor. Using the same “shutter speed” but different photosite size / type, you definitely get added DR as Fuji has proven. I think their S3 or S5 still tops the charts for it’s JPG default output DR.

My bet, however, is that this concept is as probable as a digital B&W or digital panoramic sensor. ;-) What we’re more likely to see is, improved DR using different ISO’s, through simple advances in current “Active D-Lighting” technology. If for example I shoot a landscape at ISO 100 or ISO 50, but the sensor can boost shadow sensitivity to 200 or 400, well, that’d be decent. Or if I shoot a D3s at ISO 1600 haha, I could gather better shadows by blending ISO 3200 and 6400 into the shadow pixels… Not perfect, but a small advantage with no jeopardizing of shutter speed for low-light sports / action photographers.

=Matt=

What I would like to do is compare the 1D Mk IV to the 7D to see if the nearly $3,000 price difference is worth it. Some of the reviews I’ve seen that it’s definitely not, apart from higher ISOs and 2 more fps.

I found your post looking for information of another idea that I had. What if like in your scenario you only measure full saturation but instead of sampling over time you sample over space. Imagine an array of pixels with decreasing saturation limits (for simplicity assume halving). If in any time interval we reach saturation we record a bit. Now we have a 1 bit posterized image of the places where light hit with greater than a certain intensity. Now the section with half as much sensitivity gives us a one bit image of where the light hit with twice as much intensity. We continue building this array with as many steps as the total number of stops we wish to capture letting us choose the amount of dynamic range we capture. Now we have a heavily posterized image (film was binary in this manner as well) we can sub sample with another binary string offset by 1/2 and get twice as many gray scale graduations.

The merit of this idea is that it allows for very high resolution DSLR sensors are not feature size limited (as shown by 1/2.3″ sensors with comparable resolution) the limiting factor for this system is then decoupled from the read noise and dependent only upon thermal noise. Furthermore if we build our sensor in such a way that we can program the initial charge (like memory and likely rather slow) we can then set the sensitivity and the dynamic range (we can choose our significant figure -> range ratio) on the fly per scene.
Truly though I see the strength of my idea simply to be as a novel idea in order to increase resolution. flash memory has much higher densities than sensors so the resolution is possible. This also opens ideas for different modes of sensing instead of using the photovoltaic effects we could use photoresistive materials to act as our photon counters.

Viewfinders are not just viewfinders for pros who rely on the viewfinder for every shot to compose the image. Any improvement in the viewfinder is welcome and advantageous. The viewfinder in the 7D is very good.

The movie making capability of both the 7D and 1D4 is remarkable, as evidenced by what is being accomplished in the short time since it has been available. Nikon’s movie capability is paltry in comparison.

I do totally agree that it is nonsensical and nothing more than marketing hype for Canon to increase pixel density to a point that is beyond what their lenses can resolve and to a point that results in a less than steller signal-to-noise ratio. In fact, that is the reason why I will not be purchasing the 7D for myself. [Had the 7D been issued as a 10mp or 12mp APS-C camera, I would have purchased one.]