Hi, we have a different opinion between my brother and me about a so basic and at once vital conception like resolution. I hope a enquiry about it be appropriate in this forum. I put below the two versions and I would be grateful for any help in order to determine which is the right one. Thank you very much indeed in advance.

Version 1:

1.a. The image size professionally is, in both analog and digital, measured in metric units (centimeters and its multiples or inches). And the resolution is always measured in pixels/metric unit. The result of this two variables (which is a specific amount of pixels) is, in general conceps in digital photography, only the resulting amount of pixels, only that. Finding a reason for what in some digital cameras is erroneously spoken about «image size» in pixels without that image being for the web, I find that really there is a fixed relation between size and pixels, independently of resolution, but it refers to the image file’s size, measured in MB, which certainly is always directly proportional to the amount of pixels.

1.b. When we do a photo with a digital camera, the size is always the same, those that lens is able to catch. And resolution is the amount of pixels in which that photo is going to turn into, in other words, the density of pixels that a size of photo is going to be: those that lens is able to catch and give to the «scanner» of the camera in order to transform it by the scanner in a whole spectrum of pixels, and which is going to determine the accuracy of the photo’s details, that is: its resolution.

Version 2:

2.a. In photography with digital camera, resolution (px/cm, px/inch) doesn’t exist, photography with digital camera exclusively works with image size in pixels, which is named resolution. The same occurs in digital image in screen (for example web, also screen proyection): photography with digital camera exclusively works with image size in pixels, which is named resolution.

2.b. In photography with digital camera, the size of the caught photo isn’t always the same: generally, the photosensor is a Area Array CCD, that consists in a reticulated matrix of hundred of thousands of microscopic photosensitive cells (photodiodes). Each photodiode matchs with one pixel, so the more photosensor the CCD have, the better the quality obtained with the camera will be. Those number of photosensors can be associated to a physical size (that which they themselves take up inside the camera, that isn’t the one of the image because it doesn’t exist as we physically know it), this physical size in any case would be variable by changing the resolution with which we take the photo (size in pixels x pixels).

Hi there, cjparra, welcome to RP :bigthmb:

Not very easy reading there, though 2) seems a little closer.
Try thinking another way....

When something is purely digital the only thing that makes any sense is total pixel dimensions.

However this purely digital image has to have some interfaceswith the real world and this is where the pixels/inch stuff comes in. The interfaces are at the entry point (scanner / camara), the manipulation (monitor) and the final product (printing).

In short there is no such thing a resolution for the digital image file, only pixel dimensions.
Resolution at the interfaces is just a measurement of the quality (or the settings) of the equipment being used to translate between the digital and analogue worlds.

Hope this helps a bit, if not just ask more.

Rô

Of course your reply definitely helps. Only a doubth: in a digital camera (even though I know this forum isn't about digital photograph), can you set the resolution (px/inch or px/cm) of the image or you only can set its size (px)¿¿?? And, could you say anything about the second question: with digital camera is possible to talk about the physical size of the caught photo or the physical size doesn't exist because in the camera we only have pixels¿?

Inside the camara there is a little array of CCD's (or something similar). This array has a pre-defined quantity of elements which correspond to the pixel capacity of the camara.
The lens adapts any analogue image (from a postage stamp to the moon) entering the camara to fall on the array. All of this optical stuff is completely variable, but the end result will always be fixed number of pixels.

Resuming: Digital Camara = Light in - pixels out.

There is no place where you can meaningfully talk about px/inch, except at the CCD sensor - and that measurement only interests camara makers and not camara users.

Rô

Quite clear. Thanks for all Rô

Just one thing to add here.

On some cameras there are settings that will allow different portions of the CCD to be used, thus the total number of pixels in the image can be varied.

This is done to enable more images of less quality, or fewer of greater quality, to be stored on a memory stick.

Yes, in fact the size of the image in pixels, I think. Thanks for reply