Pentax K10D has a 10.0MP APS-C
(23.5 x 15.7 mm ) sized CCD sensor . On the other hand, Pentax K-7 has a 15.0MP APS-C
(23.4 x 15.6 mm ) sized CMOS sensor and features Prime II processor.
Pentax K-7's sensor provides 5MP more than Pentax K10D's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the K10D and K-7 sensor size comparison.
Pentax K10D and Pentax K-7 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.
DxOMark Sensor Scores
Both Pentax K10D and Pentax K-7 sensors have been tested by DxoMark. DxoMark scores camera sensors for color depth (DXO Portrait), dynamic range (DXO Landscape) and low-light sensitivity (DXO Sports), and also gives them an overall score. Of the two cameras that we are comparing, K10D has scored 66, 5 points higher than K-7.