Datenblatt-Suchmaschine für elektronische Bauteile |
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ADCS-2021 Datenblatt(PDF) 4 Page - Agilent(Hewlett-Packard) |
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ADCS-2021 Datenblatt(HTML) 4 Page - Agilent(Hewlett-Packard) |
4 / 8 page 4 Setting Exposure and Gain The exposure of an image is a function of the exposure and gain registers. Exposure sets the length of time each pixel inte- grates the light (shutter speed). Gain settings allow pixel values to be amplified. Gain values from 1x to 40x are allowed, but higher gain settings amplify noise (much like higher ISO film speeds are grainier). It is best to use the lower gain settings for better images. Gains from 1x to 10x are generally recommended. Note in Table 2, there are two green gain registers, one for the odd number row green pixels and one for the even number row green pixels. The green color filters can be slightly different between rows and this allows fine-tuning. Using the same gain setting for both green registers is usually enough. Since the blue channel is not as sensitive, using blue gains approximately double that of red and green will allow the A/D full range on all three channels. Using a MacBeth Color Checker is a good way to judge exposure and color balance. A good raw image will have a good grey scale (the bottom patches on the chart). Gain settings should be adjusted so the red, green, and blue values are equal on any one grey patch. After setting gain, the exposure registers should be adjusted for a good exposure. There are three exposure registers (see Table 3). Table 2. PGA Gain Register Settings. Register Name Mnemonic Address (hex) PGA Gain Register: Green ERECPGA 0x0F PGA Gain Register: Red EROCPGA 0x10 PGA Gain Register: Blue ORECPGA 0x11 PGA Gain Register: Green OROCPGA 0x12 Table 3. Row Exposure Register Settings. Register Name Mnemonic Address (hex) Row Exposure Low Register ROWEXPL 0x13 Row Exposure High Register ROWEXPH 0x14 Sub-Row Exposure Register SROWEXP 0x15 The row exposure high register (upper 8 bits) and row exposure low register (lower 8 bits) act as a single 16 bit register. This 16 bit register sets the integra- tion time (shutter speed) of the sensor. The sub-row exposure register is used for very small changes to exposure and allow fine-tuning for exact shutter speeds. Proper exposure will result in black values near 0x00 and white values near 0xFF (assuming 8 bits). All six grey patches on the MacBeth chart should have different average intensity values in the image. If the two brightest patches both appear white then the exposure is too long. If the two darkest patches both appear black then the exposure is too short. Remember that the raw image does not have gamma correction applied yet. The final grey scale image needs to be evaluated after gamma correction. Image Processing The raw data from the sensor requires image processing before a digital image is ready for viewing. Some standard steps of image processing are as follows: 1. Defective pixel correction 2. Lens flare subtraction 3. Auto-exposure 4. Auto-white balance 5. Color filter array interpolation (demosaic) 6. Color correction (3x3 matrix) 7. Gamma correction 8. Color space correction (3x3 matrix) 9. Data compression Image processing is not part of the sensor and must be supplied separately. Image processors that are compatible with these sensors are available from Agilent Technologies and selected Agilent partners. |
Ähnliche Teilenummer - ADCS-2021 |
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Ähnliche Beschreibung - ADCS-2021 |
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