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totally newbie question?!

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totally newbie question?!
« on: 31 / May / 2008, 00:11:25 »
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Hi Im thinking of getting a Canon to try out CDHK on the cameras which support CDHK. My questions is does  CDHK increase the megapixels when in RAW mode or am I limited to the 7.2 MP which is what most of the Canons on CDHK are.

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Re: totally newbie question?!
« Reply #1 on: 31 / May / 2008, 01:00:46 »
Technically, the answer is yes, RAW increases pixel count...

Practically, the answer is no.... From what I understand, the camera tosses the pixels at the edge of the frame to save processing overhead and funny fringing at the edges as the Bayer separate RGB pixels in the sensor are combined (demosaicing) into the RGB pixel of the final "picture".

3260x2445= 7,970,700 for JPEG on A720
3280x2460= 8,068,800 for RAW on A720

I measured the A720 images using RawTherapee (May be off a bit)...

Bayer filter - Wikipedia, the free encyclopedia

-Bill

Re: totally newbie question?!
« Reply #2 on: 31 / May / 2008, 12:51:58 »
does that mean that doing the CHDK might lead to results achieved by a more expensive, higher MP count camera?

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Re: totally newbie question?!
« Reply #3 on: 31 / May / 2008, 13:33:21 »
does that mean that doing the CHDK might lead to results achieved by a more expensive, higher MP count camera?

No, by itself, the few "extra pixels" are nothing... To see a difference in pixels (in my humble opinion), you would need almost twice as many to see a difference in image quality--and even then, you would probably never see the difference in quality between a 2MP camera and an 8 MP camera in a 4x6 photo printed at your local 1 hour photo shop... If you search around on places like:

Digital Camera Reviews and News: Digital Photography Review: Forums, Glossary,
        FAQ

Digital Cameras, Digital Camera Reviews - The Imaging Resource!

You can see what a suggested MP to print size would be (don't take this as "the answer", but an 8MP camera can, from what I understand, could support a 18" wide print).... Remember, how far you are from the picture matters just as much as how fine the "dots" are printed.

For example, Imaging Resource has a nice web page where you can pull up to different cameras that have shot the same scene (at different light levels--aka--different ISO settings).

Imaging Resource "Comparometer" ™ Digital Camera Image Comparison Page

For example, plug in the A720 (8MP) and the A650 (12MP) and see what differences you can fine...

There are a whole bunch of other issues that deal with Image Quality (IQ) than just MP count.

Sensor size (specifically, the size of the pixel and how much light it can capture). Lens quality, Lens size, Lens design/type, light levels, camera processing, etc. all have a huge effect on the end photograph.

In general, a dSLR is a much larger camera and can have a larger sensor... The largest about the size of a 35mm slide. This allows each site to receive a large number of photons from the subject--so there is little noise.

A P&S camera, on the other hand has a really small sensor (sometimes even more pixels than a dSLR)... The small sensor has some advantages (small lenses are easier to make accurately & cheaply vs large lenses)--so in bright light, a P&S looks like it can hold its own with a camera that costs 10x as much. However, when the light starts to fail--the small sensor can only capture a small fractions of the photons as a large sensor (each pixel is so small, only a few photons ever hit the pixal and get counted).

So, when you get to 200-1,600 ISO with a small P&S camera, you see all sorts of grain/fuzz/funny color patches, etc. because there are so few photons to count. With a large dSLR sensor, there are simply more photons to count, and less "background noise" in the counting process.

In the end, pushing up the number of pixels does not always make for a "better photograph"... and in many cases (less than full sunlight) can actually make for worst photos (all else being equal--which it never is).

What CHDK allows you to do is have better control over your camera... For example if you want to take a shot of a dark scene (nothing moving), you can now open the shutter for ~64 seconds instead of Canon's limit of 15 seconds. And instead of using 400 ISO, you can use 100 ISO and get just as bright of picture, with much less noise.

CHDK is all about control of your camera--it cannot change the hardware and make it better.

-Bill


 

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