| 摘要 |
PROBLEM TO BE SOLVED: To precisely measure the crystal grain size of a spangle even when the concentration difference between the spangle and other crystal grains is small by reflecting the light irradiated to a surface to be measured by the surface of the crystal grain to be measured, and taking the image thereof. SOLUTION: A light source 2 adjustable in the irradiating angle and light quantityθto a surface to be measured 11 is provided on the side of surface to be measured 11 of a matter to be measured 1, for example, using an Al-Z plated steel plate after surface coating treatment. An image pickup equipment 3 such as camera, CCD or the like is provided on the same side in opposition to the surface to be measured 11. The pickup image data by the image pickup equipment 3 is transmitted to an image processing device 4, and the crystal grain size in the surface to be measured 11 is calculated by the image processing device 4. By providing the light source 2 set to a prescribed irradiating angle and a prescribed light quantity, the concentration difference between a spangle and other crystal grains can be increased in the step of taking the image of the surface to be measured.
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