Digital Imaging Ch. 14

what are 3 geometric factors of an image

Spatial resolution(Sharpness), Magnification (Size distortion), Shape distortion

What is spatial resolution

sharpness of the structural edges recorded in the image

what is magnification

difference between the size of the real object and the size of its projected image

What is shape distortion

difference between the shape of the real object and shape of its projected image

High resolution=

sharp, easily defined

Low resolution=

blurry, less defined

What happens to two objects in high resolution images

clearly defined and can see two separate objects

What happens to two objects in low/ poor spatial resolution

blur together, unacceptable levels of penumbra as compared to the umbra

How can you control the degree of unsharpness

eliminate motion, reduce OID, reduce focal spot size, increase SID

what is the umbra

uniform darkness of the inner most shadow, purest form

what is a penumbra

blurry, partial shadow

cause of geometrical penumbra

it is caused from an area source that causes partial shadows around the edges of the pure shadow

the more penumbra present means___

the more blurry the image appears (Less sharp)

what 3 things is dependent upon geometric unsharpness

SOD, OID, Size of focal spot

SOD+ OID=

SID

Penumbra=

FS x OID/ SOD

The higher the OID____

the sharpness decreases (penumbra gets larger)

what is SOD

Source to object distance

what is SID

Source to Image Distance

what is OID

object to image distance

Sharpness and penumbra is ____ of each other

inverse

Sharpness equation

sharpness= SOD/OID

Just because an image is more visible doesn’t mean___

they are sharper

sharpness is measured by___

how quickly the the transition from light to dark changes

an identical image can have the same geometric factor (sharpness) but different____

visibility factors (contrast)

what factors go into sharpness

prevention of motion and optimum geometry

The less magnification___

the better resolution

How can you control magnification by positioning

maximize SID while minimizing the OID

which projection minimizes the OID of a heart shadow

PA

why does PA projection demonstrate a truer size of the heart shadow

PA places heart closer to the IR

Definition of magnification

quantitatively measured by the images size and the size of the actual object in both axes

if both the length and width of the image measure longer=

magnification is present

for magnification to be present

the pure shadow of the umbra must be larger

If umbra DOESN’T enlarge it’s ____ NOT magnification

due to blurring

Magnification (Image size/ object size) equation

Magnification = SID/SOD

Which distance is the major controlling factor in magnification

OID

Increasing OID ____ magnification

Increases

What happens to OID if we increase SOD

Decreases OID, magnification lessens

what is shape distortion

any difference between the shape of the projected image and the real object

what are the two types of shape distortion

elongation and foreshortening

Definition of elongation

image length measures longer than the real object

Definition of foreshortening

image length measure shorter than the real object

Foreshortening is always the result of the ____ being improperly aligned

Part

Elongation is always the result of the ____ or the ___ being misaligned

tube and IR

Magnification is ___changes in both axes

Shape distortion is ___ changes between both axes

equal

unequal

goal is to ___ all forms of distortion and keep ___ at an achievable minimum

distortion, magnification

Definition of resolution

ability to distinguish any two adjacent details as being separate an distinct from each other

What is resolution dependent on

contrast and spatial resolution (sharpness)

What are some factors that effect sharpness

small focal point, finer pixel size, less motion, longer SID, shorter OID