Image conversion

[Hugh]

Hi there,

I need to convert 16-bit gray-scale images into 8-bit images for image analysis.
I can use two VIs to do this: one is IMAQ Convert and another is IMAQ Shift16To8.
But all three images (16-bit original, 8-bit from IMAQ Shift16To8, and 8-bit
from IMAQ Convert)look different. I understand that such a conversion causes
resolution loss. But even two 8-bit images look different. I use vision
5 with Labview 6 for Windows 98. Thanks in advance. I could e-mail my sample
code and image file to anyone who are interested.

Hugh

[Jiri_2]

Yes, there is a difference:

IMAQ Convert: recopies the bit value of 16-bit image to 8-bit images. If the value is less than 0, it is coerced to 0, if the value is more than 255, it is coerced to 255. I think there will be a lot of white area in your image after this conversion.

IMAQ Shift16to8: It divides by 256, it is probably better. If the result is not the same, it is probably because the pixel value in 16-bit image is signed (I16), while the pixel value of 8bit image is unsigned (U8). So white in 16bit image will become half gray in 8bit image, I think. You should multiply the resulting image by 2, if you want that it is the same as 16 bit original.