LabVIEW pictures look bright or dark after being cast from 16 bits to 8 bits

LabVIEW The picture is from 16 Bit cast to 8 Look bright or dark after bit

I captured a picture with my camera 16 Bit image , And use IMAQ Cast Image VI Convert it to 8 Bit image . The image looks brighter or darker . The bit depth of the camera is 10 position . Why is that ？

answer :

If you use 10 Bit camera captures the original image , Then we are going to change it from 16 Bit representation is converted to 8 Bit indicates after , There are several reasons why the image looks different .IMAQ Cast Image VI There is one named # Shifts The input of . Although it is I32 Long integer , But its scope is forced in 0 To 8 Between integers of . When LabVIEW take 16 Bit images are converted to 8 Bit image , It shifts the data by the number of bits specified in the input , Then use only low 8 Bit represents a new image .

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If the bit depth is 10 Bit camera captures images , There will be an exception . The bit depth of the buffer that holds the image will also be explicit 10 position . When using the conversion function to convert to a 8 Bit image , If # Shifts The input is 0, Then the function will still move the image 2 position . This will make the new 8 Bits indicate that the image looks the same as the original image . If # Shifts Other non 0 Value , Function will shift the specified number of bits to the left . therefore , If the value is 1 Words , The new image will look brighter , The value is 0 or 2 Will make the image look the same as the original image , And when the value is greater than 2 The image will appear darker than the original image .

This is when deciding what target cache to use for the result of the transform function , There's a certain relationship . For example , If you use one 10 The image captured by the bit camera is converted to 8 Bit image , And then back to 16 Bit image , So depending on whether you are reusing the same image buffer , Or create a new buffer , The result will be different . If you reuse buffers , You will keep the original image 10 Bit depth . But before you will 8 Bit images are converted to 16 Bit image , The conversion function does not move the number of bits back . therefore , The values of all pixels are constant , But now their bit depth is 10 instead of 8. When you convert to 8 Bit image , First, shift , But when you switch back , They will not be displaced back . On the other hand , If you use the new buffer as the target of the conversion function , Then the new image will have the same pixel value , And its bit depth will still be 8（ Even though it is 16 Bit image ）. therefore , It looks the same as the original image .

Here's a VI Examples to demonstrate the phenomena described above . The following tests can be carried out ： Change the number of bits shifted , Or decide whether to reuse the buffer （ Be careful ： To see more clearly the difference between reusing buffers and using new buffers , take # Shift Set to 0 or 2）. This example should be matched with one set in MAX To read 10 Bit monochrome image camera use .

More details , Participate in the introduction of the following annex .

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LabVIEW The picture is from 16 Bit cast to 8 Look bright or dark after bit - Beijing Hanwen Wangxing Technology Co., Ltd (bjcyck.com)