Digital optical measurement of particle populations using reduced magnification

1. A method for determining a distribution of a parameter of a particle population comprising the steps of:

a) detecting on a pixel array of elements a plurality of images of particles in the particle population;

b) determining a number of pixels at least partially covered by each particle to form a pixel count for each of the plurality of images of the particles;

c) obtaining a plurality of weighting factors, which are the probabilities relating each pixel count to parameter values; and,

d) utilising the pixel counts and the weighting factors to determine the distribution for the parameter of the particle population.

2. A method as defined in claim 1 , wherein step (a) includes selecting an acceptable threshold for detecting the presence of a portion of a particle on an array element, and wherein step (c) includes the step of determining said weighting factors.

3. A method as defined in claim 1 , wherein step (b) further includes the step of rounding such that particles of a plurality of proximate sizes will be included in each pixel count.

4. A method as defined in claim 1 , wherein step (c) is performed by using a model, which successively places particle outlines randomly on a grid equivalent to the pixel array and determines pixel count outcomes, for predetermining the probabilities relating each pixel count to a parameter value.

5. A method as defined in claim 4 , further comprising inputting into said model information related to the shape of said detected images of particles.

6. A method as defined in claim 4 , wherein the characteristic is the cross-sectional area of the particles in the particle population.

7. A method as claimed in claim 1 , wherein the parameter is the cross-sectional area of the particles in the particle population.

8. A method as defined in claim 1 , wherein step (d) includes the steps of:

i) utilizing said pixel counts and said weighting factors to construct a set of linear equations, and

ii) solving said set of linear equations to determine said distribution of the parameter of said particle population.

9. In a system for analyzing a parameter in a particle population in a fluid, wherein particles are substantially randomly distributed, and particles range in value from X 1 to X 10 , in increments, values of X 1 , through X 10 being different values, a method of determining a total number of particles within a sampled volume having a predetermined parameter value, comprising the steps of:

a) using a detector array of pixels to detect a plurality of images of the particles;

b) counting a number of pixels Y 1 , Y 2 , Y 3 , through at least Y 10 corresponding to each of the plurality of images of particles;

c) determining a plurality of weighting factors P(X M :Y N ) corresponding to different pixel counts from Y 1 through at least Y 10 , wherein P(X M :Y N )=the probability of a particle with a parameter value X M will occupy a pixel total Y N , wherein M can take on values from 1 rough at least 10 and X can take on values from at least 1 through 10

d) determining D(X M )=the total number of particles within the volume sampled having a parameter value X M , by solving a set of linear equations of the form:

Y 1 =D ( X 1 )× P ( X 1 ,Y 1 )+ D ( X 2 )× P ( X 2 ,Y 1 )+ D ( X 3 )× P ( X 3 ,Y 1 ) . . . P ( X 10 ,Y 1 )

Y 2 =D ( X 1 )× P ( X 1 ,Y 2 )+ D ( X 2 )× P ( X 2 ,Y 2 )+ D ( X 3 )× P ( X 3 ,Y 2 ) . . . P ( X 10 ,Y 2 )

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Y 10 =D ( X 1 )× P ( X 1 ,Y 10 )+ D ( X 2 )× P ( X 2 ,Y 10 )+ D ( X 3 )× P ( X 3 ,Y 10 ) . . . P ( X 10 ,Y 10 ).