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Monday, November 16, 2009

Basic in Image Sensor

Since I started this blog, there are more and more people asking me questions regarding dSLR. Most of them didn't rush out the door to get one after I've told them the advantages, mainly due to the price, of course. But I can see all of them are very interested in photographing. The main obvious advantageous is, of course, the sensor size. In which I realise lots of people do not understand how it works. So here go a short tutorial on sensor & megapixels myth. (to fill my blog coz no updates also =P)

Image Sensor found in Nikon D90

Ages ago when we are still living in the caves, we do not know what is megapixels. It does not exist, and all we care is not the camera built quality, but the film itself. There are high & low quality films that determines the outcome of our photos. Film SLR is only used by professional with professional interchangable lens.

Things started to get complicated when the 0 and 1 come into pictures, the logic for electronics world. Imagine a sensor is actually a solar panel, it's the same actually, so no need to imagine. It take in lights wavelength and convert it into electrons. This electrons will then be fed into the image processor for processing.

35mm Full Frame:  Nikon D700, Nikon D3, Canon 5d

APS-C (Nikon) : Nikon D300, Nikon D90, Nikon D5000

APS-C (Canon): Canon 50D, Canon 500D, Canon 1000D

Four Thirds System: Olympus PEN-E-P1

1/1.63": Panasonic Lumix DMC-LX3

1/1.7": Canon Powershot G9, Canon Poweshot SD950IS

1/1.8": Nikon Coolpix P5000

1/2.5": Canon Powershot A570IS, Canon IXUS 860IS, Sony Cybershot DSC-W80, Sony Cybershot DSC-H9

The sensor size is actually equivalent to a film size. The normal film size we normally used is 35mm measured in sensor length. Same goes to sensor size. Looking at the table, the only equivalent quality of sensor to the normal 35mm film we used ages ago is the full frame sensor in highest specifications of dSLR! After so many years, we finally picking up to what our grandfather is using. Funny, but true. Most compact are 1/2.5" sensor size, and that explains why the quality is not comparable to a dSLR.

The 2nd affecting factor is the pixels. Imagine a piece of land (the sensor size) is built with concrete divider that separate the the entire piece of land into 800 equal lengths and 600 equal widths. Each concrete box is a pixel. The land now have 800x600 pixels or equivalent to 480,000 pixels. Pixels is defined without considering the size of the sensor, therefore, imagine cramming 10,200,000 pixels (10.2megapixels) into that tiny 25mm2 (1/2.5") size while the same pixels is comfortably fit into the 864mm2 (35mm) sensor. These small pixels/dots will combine becoming a photos. That my friend, is the power of technology and different in quality.

Pixel Art in low pixel array arrangement

Once you understand this, you will know that why megapixels does not matter because the sensor size is limited. No matter how many megapixels you throw in, the size is still the same. Of course that it's still important that higher megapixels sensor do provide higher resolution, in which avoid pixelisation during large printout. However, it's still only a very minor unnoticable improvement over the advantageous offer by larger sensor.

However, do take note that pixelisation (boxy edge) still will happen if you use a small megapixels setting in dSLR and print out the photo in a very large poster paper. That's when the megapixels come into the picture. Other than that, it's not noticable in small printout out like 4"x3" photos we normally keep. Considering the photos printer is 300dpi (dots per inch), then your 4"x3" photos will need 1,200 x 900 pixels/dots only. All other pixels will be deleted during printing, just because the printer cannot make use of the rest of the pixels. So, why bother shooting higher resolution?

I kept my D90 setting to highest resolution but maximum jpeg compression. That give me the highest resolution, and I rely on the camera processor to "intelligently" compress the non-relevant pixels in my photos. I will normally get 3-4Mb for each photo that I've taken in 4288x2848 (12.2megapixels). If you take raw, you should get size of the photo similar to the megapixels, in this case, 12.2Mb. As I said, each pixel is converted into 0 or 1, therefore 1 bytes for 1 pixel =)

Jpeg compression in Fine or Normal determines the rate of compression you choose. It's similar to zip or rar program that we used in documents. Just that this time, the camera will determine which pixels is not important / repetitive in the photos to human eyes, that will still produce the same quality. It should be the best quality to size combination. If there is a job, then I will start shooting RAW, but not now.

There are still other technology considerations in sensor advantageous, which too vast to cover. Maybe next post. Those are like CCD, CMOS, sensor built, how lights is captured, noise, colour, different in Nikon / Canon system and etc. I shall write more when I'm free. Thanks for listening and do correct me if I'm wrong somewhere.


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