首先需要使用CaptureRequest.Builder来设置相机参数，并设置CaptureRequest.CONTROL_AE_MODE的值为CONTROL_AE_MODE_OFF，这将禁用自动曝光程序，使我们可以手动设置所有的曝光相关参数。然后，需要使用CaptureRequest.Builder.set(CaptureRequest.SENSOR_SENSITIVITY, iso)和CaptureRequest.Builder.set(CaptureRequest.SENSOR_EXPOSURE_TIME, shutterSpeed)来设置曝光时间和ISO值。同时，我们可以使用CaptureRequest.Builder.set(CaptureRequest.CONTROL_AWB_MODE, awbMode)来设置白平衡模式。最后，可以使用CaptureRequest.Builder.set(CaptureRequest.CONTROL_AE_EXPOSURE_COMPENSATION, exposureCompensation)来设置曝光补偿值。这些参数都需要根据实际的情况来进行调整。以下是设置伽马值的代码示例：

//禁用自动曝光程序
mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AE_MODE, CameraMetadata.CONTROL_AE_MODE_OFF);

//设置曝光参数
mPreviewRequestBuilder.set(CaptureRequest.SENSOR_SENSITIVITY, iso);
mPreviewRequestBuilder.set(CaptureRequest.SENSOR_EXPOSURE_TIME, shutterSpeed);

//根据实际需求设置白平衡模式
mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AWB_MODE, awbMode);

//设置曝光补偿值
mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AE_EXPOSURE_COMPENSATION, exposureCompensation);