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Resolution Loss During Transfer                 Back to Notes on Photography
by Makoto Honda                September 13, 2005


General

As described in the previous article, we can obtain the total dot count in the image from the resolution, given the area size: Resolution -- Area Size -- Height & Width Dots -- Total Dot Count.

1.  Resolution - expressed in lp/mm (line pairs per millimeter)
2.  Area Size - expressed in width and height in mm
3.  
Dots (height & width) - dot counts along the height and width of the area
4. 
Total Dot Count (area) - height dots times width dots

We are mainly interested in the total dot count of the image captured on the film or the digital sensor. Here, we show how the resolution is decreased at each step in the photographic process where the transfer of image takes place, such as transfer to film and transfer to digital sensor (digital capture) during digital shoot/digital scan.

(1) Taking Pictures with Film

This is a traditional film photography. An image is formed by the lens at its focal plane. The total dot count in the image is based on the lens resolution. A film is placed at the focal plane to capture the image on the film (transfer of image to film). The film resolution dictates the total number of dots the film can possibly capture. The image actually captured on the film has the total dot count based on the final image resolution, which is a function of both lens and film resolution.

(2) Scanning the Film

The film created by the process (1) above is scanned by the digital scanner (transfer of image to scanner sensor). The image (on the film) being scanned has the resolution described above. The scanner sensor has its own resolution (often expressed in dpi). The final digital image captured by the scanner has the total dot count dictated by the resultant image resolution, which is a function of the resolution of the image (on the film) and the scan resolution.

(3) Taking Digital Pictures

Here, we are using a digital camera to take a picture. As in the film photography, an image formed by the lens is captured by a recording medium, in this case, a digital sensor (transfer of image to camera sensor). Again, the total dot count in the digital image captured on the sensor is calculated from the final image resolution, which is a function of the lens resolution and the digital sensor resolution. Since the camera directly produces a digital image, the additional scanning process is not needed, thus forgoing the loss of resolution in the scan.

 

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