*Appendix 1*

*Area measurements for
"gain in image size" and pixel density*

This
appendix is part of * this article* about the “telephoto advantage”
and "pixel density advantage" of an APS-C camera.

We have dealt with the “pixel density advantage” of
APS in terms of the **width **of the
full sized image of APS, compared with the
**width** of the cropped image of FF.
However, it is also possible to look at this advantage in terms of the
percentage difference between the pixel count (expressed in **
megapixels) **of the comparable images of APS and FF. Calculating
megapixels, is just like calculating the
**area **of a photograph. For example, a photograph that measures, say,
6 inches x 4 inches, has an area of 24 square inches.

**Gain in image
size based on the pixel counts of the images (expressed in megapixels)**

The uncropped image of APS has 15.36 megapixels (4800 pixels x 3200 pixels). In contrast, the cropped image of FF has 10.67 megapixels (4000 pixels x 2667 pixels).

Therefore, the “total area” gain in image size of APS is 44%, because the pixel count of APS is 44% greater than the pixel count of the cropped image of FF (15.36 megapixels / 10.67 megapixels).

We shall now use the *megapixels per square
centimetre *method to show that this 44% gain can be reconciled with the
percentage difference between the pixel densities of APS and FF.

**
Megapixels per square centimetre method**

Under the *
megapixels per square centimetre method,* pixel density is calculated by
dividing* *the*
*number of megapixels on the sensor, by the sensor area in square
centimetres. Therefore, in this example, the pixel density for APS is
**4** (15.36 / 3.84), and for FF it
is **2.778** (24 / 8.64). So, in this
example, the pixel density of APS is 44% larger than that of FF (4 / 2.778).

This reconciles with the pixel count (expressed in
megapixels) of the full sized image of APS, which is **also **
44% greater than the pixel count of the cropped image of FF (15.36
megapixels / 10.67 megapixels).

** Note: **The above arithmetical
reconciliation works exactly,

*
Appendix 2*
of the above article provides calculations of the estimated width
and area of one pixel, and shows the relationship of these calculations to
image size and pixel density.

*
Appendix 3* provides a very valuable summary of the
mathematical relationships between image size, pixel density,
and pixel size. The information in Appendix 3 can be used as a template for
calculating the pixel density and pixel size of any camera with a 3:2 aspect
ratio.

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