What is the characteristic curve.
The relationship between the exposure and density is plotted in a curve is called characteristic curve. The characteristics curve was published in England in 1890. It is also called H and D curve because this curve was published by F. Hurter and V.C. Driffield . The film density is plotted on the vertical axis and the film exposure on the horizontal axis. The shape and location of this curve is very important. The curve is sigmoid shape and it have three portion called toe, straight line and shoulder. The toa is the low exposure region and the shoulder is the high exposure region of the curve. Base plus fog level is the film blackening in the absence of any radiation exposure and typically range from 0.1 to 0.2 OD units. It refers the background fogging and the tinting ( blue) of base . The maximum film density ranges from 2.5 to 3.0 OD.
All the radiolological technique should produce a density in The straight line portion. The contrast is related to the slope of linear portion of the curve. Higher the slope higher the image contrast. The parameter which describes the contrast of the film is called average gradient.
Fig :- Characteristic curve
What is the importance of the characteristic curve.
The practical importance of the characteristics curve are:-
1) The characteristics curve shows the fog length of film used
2) The characteristics curve help to two film can be compared for their speed.
3) The contrast of film can be read from the slope of curve
4) To compare relative screen speed.
What are the three parts of a characteristic curve.
The curve is sigmoid shape and it have three part called toe, straight line and shoulder.
What is the H and D curve.
characteristic curve is also called H and D curve because this curve was published by F. Hurter and V.C. Driffield.