Projection display apparatus

1. A projection display apparatus comprising:

a light source;

an optical modulator element for modulating incident light from the light source with an input signal;

a projection lens for magnifying and projecting outgoing light from the optical modulator element;

a pixel shift element disposed between the optical modulator element and the projection lens, and displacing an optical path of the outgoing light from the optical modulator element for shifting a display position of a pixel to be displayed on a screen in a given cycle between a first position and a second position away from the first position by a predetermined distance; and

a controller for controlling the pixel shift element in a first mode and a second mode,

wherein the controller controls the pixel shift element such that the pixel shifts between the first position and the second position and the controller operates in one of the first mode at a shift speed or the second mode at another shift speed depending on a received command.

2. The projection display apparatus according to claim 1 , wherein the first mode is a video mode in which the optical modulator element modulates the incident light supplied from the light source with a video signal, and emits the light as image light,

the second mode is an illumination mode in which the optical modulator element emits the incident light supplied from the light source as illumination light based on an illumination signal, and

the shift speed of the pixel in the illumination mode is slower than the shift speed of the pixel in the video mode.

3. The projection display apparatus according to claim 2 , wherein

the controller controls the pixel shift element such that:

in the video mode, the pixel shifts between the first position and the second position in a rising period and a falling period of a rectangular waveform that represents a relation of time vs. pixel shift quantity, and

in the illumination mode, the pixel shifts between the first position and the second position in a peak-to-peak period within a half cycle of a sign-waveform that represents a relation of time vs. pixel shift quantity.

4. The projection display apparatus according to claim 2 , wherein

the controller controls the pixel shift element such that the pixel shift quantity in the illumination mode differs from the pixel shift quantity in the video mode.

5. The projection display apparatus according to claim 2 , wherein

the controller controls the pixel shift element such that, in the illumination mode, the pixel is located at the first position or at the second position at a timing when color light of low brightness enters the optical modulator element from the light source.

6. The projection display apparatus according to claim 2 further comprising a spatial frequency detector that determines whether the input signal is in the video mode or in the illumination mode based on a spatial frequency of the input signal,

wherein the controller controls the pixel shift element based on the determination done by the spatial frequency detector.

7. The projection display apparatus according to claim 2 further comprising a letter-display signal generator,

wherein a letter display period and an illumination display period are provided in the given cycle,

wherein the optical modulator element emits display light based on a letter signal supplied from the letter-display signal generator in the letter display period, and emits illumination light based on the illumination signal in the illumination display period, and

wherein the controller controls the pixel shift element in the video mode during the letter display period, and in the illumination mode during the illumination display period.

8. The projection display apparatus according to claim 1 , further comprising a detector which detects a characteristic of the input signal to provide a result, the received command is issued in response to the result.

9. The projection display apparatus according to claim 1 , wherein

a plurality of pixels are displayed on the screen,

each of the plurality of pixels is formed of a pixel section and a black region that is observed between pixel sections adjacent to each other, and

the pixel section is larger than the black region.