Unit 2B-Digital Image Post Processing Flashcards
What does the S curve in a film system show?
S curve shows the relationship between the amount of exposure and the optical density
T/F
For film screen images, the curve is S shaped with a short dynamic range (lattitude)
True
T/F
In digital imaging, we have infainate shades of grey
True
What shape is the graph depicting shades of gray in digital receptors?
Linear
Why does the raw image in DR systems look washed out?
The human eye cannot process all of the shades of gray, which is why a washed out appearance is visible prior to post processing
In electronic imaging processing terms, the S shaped charecteristic curve is called what?
The look up table (LUT)
How does the LUT change your image?
It relates an input optical density value to an output optical density to create a good contrast image by the computer selecting the correct LUT for the body part
What is the purpose of histogram equaliztaion?
To bring all portions of the image into the range in which the LUT has a steep slope so that maximal contrast is provided
How many steps are there in unsharp mask filtering?
3 steps
(almost like dual energy scan)
What is step one of unsharp mask filtering?
An image is created from the original image that has detail removed by a low pass filter
What is step two of unsharp mask filtering?
A postive of the unsharop mask is made by inverting the pixel values
What is the third step of unsharp mask filtering?
Subtract the positive mask in step 2 from the original image in step one
What are the pros of unsharp mask filtering?
-High detail image
-Good for identifying lines and tubes
What are the cons of unsharp mask filtering?
Image is noisy
What are the pros of image smoothing?
Reduction of noise and increase of contrast resolution
