FLIR Camera Adjustments LWIR Video Camera Application Note FLIR Commercial Systems 70 Castilian Drive Goleta, CA 93117 Phone: +1.805.964.9797 www.flir.com Document Number: 102-PS242-100-01 Version: 110 Issue Date: June 2014...
FLIR Camera Adjustments Table of Contents FLIR Camera Adjustments ........................... 1 LWIR Video Camera ............................ 1 Application Note ............................1 Document Number: 102-PS242-100-01 ....................... 1 Document ............................4 Revision History ........................... 4 Scope ............................. 4 Automatic AGC Parameters......................5 Introduction to Histograms ......................6 Linear Histogram ..........................
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FLIR Camera Adjustments Figure 19: Illustration of Active Contrast Enhancement (ACE) ..............17 Figure 20: Illustration of Smart Scene Optimization (SSO) ............... 18 Figure 21: Illustration of ROI ........................19 Figure 22: Illustration of the difference between Plateau Equalization, Information-based, and Information-based Equalization algorithms ....................
This document applies to the FLIR Quark, Quark 2, Tau, Tau 2 and Neutrino cameras. These cores can be found in most FLIR Commercial Systems products. The FLIR website will have the newest version of this document as well as offer access to many other supplemental resources: http://www.flir.com/cvs/cores/resources/...
FLIR Camera Adjustments 2.0 Automatic AGC Parameters The first thing to understand is that the detector data is directly streamed from the sensor as 14-bit values for each pixel in the array. The analog image is displayed using 8-bit values and almost all commercial displays are 8-bit devices.
Generally speaking, FLIR recommends the plateau equalization algorithm, but there are scenarios where each of the other algorithms may be better suited. The FLIR GUI provides auto presets that can be used to tune AGC to the specific scene.
FLIR Camera Adjustments has a narrow spike whereas the mug has different temperatures in the handle and above the coffee line. For this reason, the data is more spread in the histogram at point 3. Figure 2: Image of scene 2.2 Linear Histogram...
FLIR Camera Adjustments The linear histogram algorithm performs a linear transformation from 14-bit to 8-bit of the form: 8bit = m * 14bit The slope of the transformation is computed automatically based on the ROI histogram: m = 255 / (14bit_(100 – Tail Rejection)% - 14bit_(Tail Rejection)%), where 14bit_(Tail Rejection)% is the 14-bit value corresponding to the user selectable tail rejection percentage point on the cumulative ROI histogram and 14bit_(100 –...
FLIR Camera Adjustments redistribute the data to achieve this goal. This prevents wasted levels of grey on regions that have no scene content and can visually be seen in the histograms by noticing that peaks are much smoother and the data is spread much more evenly.
FLIR Camera Adjustments Low Contrast Histogram Equalized Low Contrast conversion Linear 14 to 8 bit Lots of Contrast Figure 6: Image Transform Table for Linear and Plateau algorithms In many applications, there are objects with different temperatures that all need to have contrast. In this case, the plateau value can be increased from the default setting of 150 to 250 or 300, depending on the content of the scene.
FLIR Camera Adjustments It is also important to note that changes in levels of grey are more perceptible to a human observer at lower levels of illumination. This is because a change from 5 to 10 counts is 100% and a change from 245 to 250 is about 2%.
FLIR Camera Adjustments Figure 9: Low contrast scene in 14-bit space. The large spike from the wall is the same value as in initial histogram. The following histogram shows the 8-bit data with the default Max Gain setting of 8. Notice that there is a large amount of unused levels of grey on the left and right of the signal.
FLIR Camera Adjustments Figure 13: Low contrast scene: high gain Figure 12: Plateau: 250, ITT: 127, Max Gain: 25 Figure 14: Plateau: 250, ITT: 127, Max Gain: 50 Figure 15: Low Contrast Scene: very high gain The plateau equalization algorithm performs a non-linear transformation from 14-bit to 8-bit based on image histogram.
FLIR Camera Adjustments Plateau value. When plateau value is set high, the algorithm approaches the behavior of classic histogram equalization – gray shades are distributed proportionally to the cumulative histogram, and more gray shades will be devoted to large areas of similar temperature in a given scene. On the other hand, when plateau value is set low, the algorithm behaves more like a linear AGC algorithm –...
FLIR Camera Adjustments Maximum Gain. For scenes with high dynamic range (that is, wide 14-bit histogram), the maximum gain parameter has little effect. For a very bland scene, on the other hand, it can significantly affect the contrast of the resulting image. Figure 17 provides an example.
FLIR Camera Adjustments ITT Midpoint. The ITT Midpoint can be used to shift the 8-bit histogram darker or brighter. The nominal value is 128. A lower value causes a darker image, as shown in Figure 18. A darker image can help improve the perceived contrast, but it is important to note that more of the displayed image may be railed (8bit value = 0 or 255) by moving the midpoint away from 128.
0 do the opposite by decreasing contrast for hotter scene content and leaving more of the gray-scale shades to represent the colder scene content. Figure 19 illustrates the effects of ACE. FLIR recommends a conservative setting of 3 for generic use-case scenarios.
14-bit histogram prior to AGC. This feature is useful for excluding outliers and the most extreme portions of the scene that may be of less interest. FLIR recommends tail rejection settings less than 1% to avoid the exclusion of important scene content.
FLIR Camera Adjustments For Tau 2.0, separate ROI are automatically applied for un-zoom, 2X, 4X, and 8X zoom. Coordinates for the ROI are as follows: Top / Bottom: 0 = center of the display, negative values are above center, positive values are below center, units are in pixels ...
FLIR Camera Adjustments AGC Filter. The AGC filter is an IIR filter used to adjust how quickly the AGC algorithm reacts to a change in scene or parameter value. The filter is of the form n' = n * + n'-1 * (256-)/256...
FLIR Camera Adjustments (a) Plateau Equalization (b) Information-based (c) Information-based Equalization Figure 22: Illustration of the difference between Plateau Equalization, Information-based, and Information-based Equalization algorithms Information Threshold. The information threshold parameter defines the difference between neighboring pixels used to determine whether the local area contains “information” or not. Lower thresholds result in...
FLIR Camera Adjustments Manual The “manual” algorithm performs a linear transformation from 14-bit to 8-bit, with slope based solely on a specified contrast value and offset based solely on a specified brightness value as shown below: m = specified contrast / 64 b = 127 –...
(b) DDE index = 70 Figure 25: Illustration of Detail Enhancement with DDE Note: The recommended DDE mode is “dynamic”. “Manual” is provided for customers of previous FLIR cores that have familiarly with the manual DDE mode. Rev110 June 2014...
FLIR Camera Adjustments Manual mode: The following three parameters are user-specified: o DDE Gain: ranges from 0 to 65535 for Tau 2.7 and later releases and represents the magnitude of high-frequency boost For gain = 0, DDE is disabled ...
FLIR Camera Adjustments The Tau2 and Quark cameras contained the normal imaging LUTs which contain 256 colors or greyscale and map that to the 8-bit AGC data from the cameras. The imaging palettes are shown below. The palettes only affect the analog and BT.656 outputs of the Quark 1, Tau 2.3 and earlier releases. The Quark 2 and Tau 2.4 releases and later have an option for color in the CMOS and LVDS 8-bit data.
2 seconds (60 frames) prior to the FFC operation. The duration of the FFC Imminent Symbol can be set in the FLIR Camera Controller GUI using the FFC Warn Time setting in the Analog Video Tab. Setting the Warn Time to less than 15 frames turns off the warning. When using analytics, this warning might induce false alarms and it is recommended to either disable this feature or create a region to ignore this area.
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