Advanced Photography Course

Range--the difference between the largest and
smallest numbers of the set

Deviation--the amount each element of the

population is away from the mean

Standard error--the average percent of

deviation from the mean

CONTROL CHART INTERPRETATION

Control charts for film processing should be

maintained as long as the process is in operation. For
control charts to be of value, you should remember
the following guidelines:

There must be a continuous analysis of a
statistical nature of photo-processing control
charts.

It is pointless to maintain control charts, then
fail to act when the chart indicates a problem

in the process.

Control charts let you visually determine a
definite processing problem occurring among
random process variations.

There is always a certain amount of natural
variability in a process.

There can be overcontrol, as well as

undercontrol, in precision quality assurance
processing. Overcontrol of a process can be
needlessly expensive.

These guidelines cannot be overemphasized and

should become an integral part of your processing
philosophy. Each process control chart you maintain

can illustrate five possible conditions of that process.
These conditions depend upon variations within that
process. These five conditions are shown in figure
2-15.

A normal pattern exists in all processes that are

operating correctly. This pattern reflects the

variability that cannot be controlled or eliminated
completely. When an out-of-control condition exists,
immediate action should be taken to correct the
problem. When the chart shows a trend in five
successive recordings, this is a good indication that
the process is changing and requires investigation with

possible corrective action. A run is when five
successive recordings appear above or below the mean
line. This also requires investigation and possible
corrective action. A jump may indicate that a problem
exists and requires correction before the process gets
out of control.

Evaluating Process-Monitoring Charts

To be useful, you must be accurate with a control

chart and you must analyze it at least daily.

PLOT PATTERNS.--

Plots, or points, on a

control chart should be thought of as patterns or
groups and not as individual points. It is not enough
to know where a plot is; you must also know how it
got there. In process monitoring, you must be able to
recognize patterns that indicate when a process is
moving toward an out-of-control condition. After a
value is plotted on a chart, the point is connected to
the previous point with a straight line. This provides
a graphic representation of variations in the process
and whether the desired processing conditions are
being maintained.

TRENDS.--

A drift of plotted points either

upward or downward, away from the established
mean, with no sudden change in direction is called a
trend pattern. A trend usually consists of at least five
plotted points. An upward or downward trend usually
indicates over- or underdevelopment, respectively.
The processed images will be either increasing or
decreasing in both density and contrast. A trend that
is gradual may be an indication of too much or too
little replenishment.

JUMPS.--

A plot point that jumps or suddenly

moves away from previously plotted points may be

caused by contamination of the chemistry, improperly

mixed chemicals, or mechanical breakdowns, such as

replenisher systems or thermostats. A jump pattern is
likely to occur after a process has been shut down,
especially if the process has not reached the proper
operating temperature.

RANDOM PATTERN.--

Whereas trends and

jumps must be analyzed to determine their probable

cause and corrective action taken when necessary, a
random pattern within control limits indicates that the
process is in control and is not moving toward an
out-of-control condition. When an in-control random
pattern is maintained, solution strength is probably
normal and no correction is necessary; however, when

2-28

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Advanced Photography Course

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DOFMaster for Windows On-line Depth of Field Calculator DOFMaster for Mobile Devices On-line Depth of Field Table Hyperfocal Distance Chart Articles FAQ Recommended Books Support Contact Links Home As an Amazon Associate I earn from qualifying purchases.	contents <- previous page next page -> Range--the difference between the largest and smallest numbers of the set Deviation--the amount each element of the population is away from the mean Standard error--the average percent of deviation from the mean CONTROL CHART INTERPRETATION Control charts for film processing should be maintained as long as the process is in operation. For control charts to be of value, you should remember the following guidelines: There must be a continuous analysis of a statistical nature of photo-processing control charts. It is pointless to maintain control charts, then fail to act when the chart indicates a problem in the process. Control charts let you visually determine a definite processing problem occurring among random process variations. There is always a certain amount of natural variability in a process. There can be overcontrol, as well as undercontrol, in precision quality assurance processing. Overcontrol of a process can be needlessly expensive. These guidelines cannot be overemphasized and should become an integral part of your processing philosophy. Each process control chart you maintain can illustrate five possible conditions of that process. These conditions depend upon variations within that process. These five conditions are shown in figure 2-15. A normal pattern exists in all processes that are operating correctly. This pattern reflects the variability that cannot be controlled or eliminated completely. When an out-of-control condition exists, immediate action should be taken to correct the problem. When the chart shows a trend in five successive recordings, this is a good indication that the process is changing and requires investigation with possible corrective action. A run is when five successive recordings appear above or below the mean line. This also requires investigation and possible corrective action. A jump may indicate that a problem exists and requires correction before the process gets out of control. Evaluating Process-Monitoring Charts To be useful, you must be accurate with a control chart and you must analyze it at least daily. PLOT PATTERNS.-- Plots, or points, on a control chart should be thought of as patterns or groups and not as individual points. It is not enough to know where a plot is; you must also know how it got there. In process monitoring, you must be able to recognize patterns that indicate when a process is moving toward an out-of-control condition. After a value is plotted on a chart, the point is connected to the previous point with a straight line. This provides a graphic representation of variations in the process and whether the desired processing conditions are being maintained. TRENDS.-- A drift of plotted points either upward or downward, away from the established mean, with no sudden change in direction is called a trend pattern. A trend usually consists of at least five plotted points. An upward or downward trend usually indicates over- or underdevelopment, respectively. The processed images will be either increasing or decreasing in both density and contrast. A trend that is gradual may be an indication of too much or too little replenishment. JUMPS.-- A plot point that jumps or suddenly moves away from previously plotted points may be caused by contamination of the chemistry, improperly mixed chemicals, or mechanical breakdowns, such as replenisher systems or thermostats. A jump pattern is likely to occur after a process has been shut down, especially if the process has not reached the proper operating temperature. RANDOM PATTERN.-- Whereas trends and jumps must be analyzed to determine their probable cause and corrective action taken when necessary, a random pattern within control limits indicates that the process is in control and is not moving toward an out-of-control condition. When an in-control random pattern is maintained, solution strength is probably normal and no correction is necessary; however, when 2-28 contents Advanced Photography Course <- previous page next page ->	As an Amazon Associate I earn from qualifying purchases.
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