If pixel sizes differ from sensors... why they are equal when printing?

[ricardo_villagran]

Maybe is a dumb question, but I cannot find an answer to this...

 

 

I read at DPreview.com:

 

"Sensors of digital compact cameras are substantially smaller than those of digital SLRs

with a similar pixel count. As a consequence, the pixel size is substantially smaller, which

is a key reason for the image quality difference, especially in terms of noise and dynamic

range.."

 

My question is, If there are different pixel sizes, why when open in Photoshop an 8MP

image coming from a Olympus 8080 with its 2/3's sensor, and one from an Oly Evolt with

a 8MP 4/3's sensor, they both have the same print dimensions? I mean, pixels have to fill a

physical space at the moment of printing, so if pixels are from different sizes, don't they

come up with different print sizes too? what is the answer?

 

 

Thanks in advance for any comment!

 

 

Ricardo V

[minicucci]

Ricardo: Take a look at this article: http://luminous-landscape.com/essays/pixel-

count.shtml. I think it answers your question.

[outrageousphoto]

A typical case of "what's in a name" What in daily life is called a pixel of a digital camera is in fact a photosite. A photosite is an electrical analog device that transformes light into an electrical current. Once that electrical signal is digitized,it is called a pixel. it is an collection of bits and- this is important- has no size at all! (How would you measure the size of an elecrical current with your caliper?)It is just something that tells your computer to put a dot with given colorvalues in given coordinates on your screen

The size of that dot depends on what you tell your computer to do with it. (print the picture 4x6 inches, show on the screen with a 600 percent magnification or show on the screen at a 100%) Hope this helps.

[mark_houlder2]

a pixel is a pixel is a pixel. whatever size the photosite it came from (ie pixel in the camera) is irrelevant to the size of the print. one camera pixel will always be equivalent to one pixel on screen (when viewing at 100%) or 1/300" on the page (printed at 300dpi), 1/1200" on the page (printed at 1200dpi) etc etc.

 

the difference in size between camera pixels (photosites) does, however, affect other things - like noise. generally speaking, the bigger the sensor, the lower the noise.

 

so if you have a 5M APS sensor vs a 5M full-frame 35mm sensor, the prints you get will be exactly the same size (if using the same resolution, eg 300dpi). BUT the larger sensor will probably look better, because there will be (among other things) less noise, due to the larger 'pixels' in-camera.

[kaur_virunurm]

Images are usually enlarged for printing. Images from smaller-sensor cameras are enlarged more and their pixels are "stretched" accordingly.

 

(It is true that a pixel itself has no real dimensions, but the image parameters assign size to them. So image resolution of 72 pixels per inch tells you - and the printing device - that each pixel is 1/72". However this parameter gets often ignored and the image is scaled to fit whatever size you want to.)

[kelly_flanigan1]

For a given technology of sensor; a smaller pixel site on a sensor is noiser. Kids are like this too; sometimes. 100 babies in a room can be noiser that 100 60 year olds.