Image signal processor, method for operating image signal processor and image sensing device

An image sensing device comprising:

• an image sensor including different first to third areas;
• and
• an image signal processor configured to receive a first pixel signal generated from the first area, a second pixel signal generated from the second area, and a third pixel signal generated from the third area, wherein:
• the image signal processor is configured to:
• perform correction on the first pixel signal to generate a first corrected pixel signal, perform correction on the second pixel signal to generate a second corrected pixel signal, and perform correction on the third pixel signal to generate a third corrected pixel signal;
• calculate a first pixel signal variance value based on the first pixel signal, calculate a second pixel signal variance value based on the second pixel signal, and calculate a third pixel signal variance value based on the third pixel signal;
• calculate a first corrected pixel signal variance value based on the first corrected pixel signal, calculate a second corrected pixel signal variance value based on the second corrected pixel signal, and calculate a third corrected pixel signal variance value based on the third corrected pixel signal;
• and
• calculate a first gradation probability value based on a comparison result between the third pixel signal variance value and the third corrected pixel signal variance value, and
• the third pixel signal variance value is greater than the third corrected pixel signal variance value.

A method for operating an image signal processor, the method comprising:

• receiving a first pixel signal including a plurality of first pixel values, a second pixel signal including a plurality of second pixel values, and a third pixel signal including a plurality of third pixel values;
• estimating a first gradient of the first pixel values, estimating a second gradient of the second pixel values, and estimating a third gradient of the third pixel values;
• correcting the first pixel values based on the first gradient to generate first corrected pixel values, correcting the second pixel values based on the second gradient to generate second corrected pixel values, and correcting the third pixel values based on the third gradient to generate third corrected pixel values;
• generating a first variance value based on the first pixel values, generating a second variance value based on the second pixel values, and generating a third variance value based on the third pixel values;
• generating a fourth variance value based on the first corrected pixel values, generating a fifth variance value based on the second corrected pixel values, and generating a sixth variance value based on the third corrected pixel values;
• determining the first pixel signal as a flat area based on a comparison result between the first variance value and the fourth variance value;
• determining the second pixel signal as an edge area based on a comparison result between the second variance value and the fifth variance value;
• and
• determining the third pixel signal as a gradation area based on a comparison result between the third variance value and the sixth variance value.