how to render in spectral mode correctly?

Summary

I'm attempting volumetric rendering with spectral rendering, but the results are somewhat unusual compared to what I expected. Due to my lack of experience with spectral rendering, I'm unsure whether the issues are due to my settings or if there are inherent errors in my parameter choices.

Description

I'm rendering in scalar_spectral mode, and my XML configuration is as follows:

<scene version="3.0.0">
    <default name="integrator" value="volpathmis" />
    <default name="spp" value="50000" />
    <default name="res" value="512" />
    <default name="max_depth" value="65" />
    <integrator type="$integrator">
        <integer name="max_depth" value="$max_depth" />
    </integrator>
    <sensor type="perspective" id="sensor">
        <string name="fov_axis" value="smaller"/>
        <float name="near_clip" value="0.001"/>
        <float name="far_clip" value="100.0"/>
        <float name="focus_distance" value="1000"/>
        <float name="fov" value="39.3077"/>
        <transform name="to_world">
            <lookat origin="0,  0.25,  -2.5"
                    target="0,  0.25,  0"
                    up    ="0,  1,  0"/>
        </transform>
        <sampler type="independent">
            <integer name="sample_count" value="$spp"/>
        </sampler>
        <film type="hdrfilm">
            <integer name="width"  value="$res"/>
            <integer name="height" value="$res"/>
            <rfilter type="tent"/>
            <string name="pixel_format" value="rgb"/>
            <string name="component_format" value="float32"/>
        </film>
    </sensor>

    <!-- Light -->   
    <emitter type="point">
        <point name="position" value="0,  0.25,  -2"/>
        <rgb name="intensity" value="15.0,15.0,15.0"/>
    </emitter>

    <!-- Shapes -->
    <shape type="obj">
        <string name="filename" value="head.obj" />
        <transform name="to_world">
            <scale value="1"/>
            <translate x="0" y="0" z="0"/>
        </transform>
        <medium type="homogeneous" name="interior">
            <spectrum name="sigma_t" value="400:0.8163, 410:0.7474, 420:0.6861, 430:0.6315, 440:0.5827, 450:0.5389, 460:0.4995, 470:0.4641, 480:0.4320, 490:0.4030, 500:0.3766, 510:0.3527, 520:0.3309, 530:0.3109, 540:0.2927, 550:0.2760, 560:0.2606, 570:0.2465, 580:0.2335, 590:0.2215, 600:0.2104, 610:0.2002, 620:0.1907, 630:0.1819, 640:0.1737, 650:0.1661, 660:0.1590, 670:0.1524, 680:0.1462, 690:0.1404, 700:0.1350"/>
            <spectrum name="albedo" value="400:0.1536, 410:0.1567, 420:0.1599, 430:0.1634, 440:0.1670, 450:0.1709, 460:0.1749, 470:0.1792, 480:0.1837, 490:0.1883, 500:0.1932, 510:0.1982, 520:0.2035, 530:0.2089, 540:0.2146, 550:0.2204, 560:0.2264, 570:0.2326, 580:0.2389, 590:0.2454, 600:0.2521, 610:0.2590, 620:0.2659, 630:0.2731, 640:0.2803, 650:0.2877, 660:0.2952, 670:0.3028, 680:0.3105, 690:0.3183, 700:0.3262"/>
            <float name="scale" value="25257"/>
        </medium>
    </shape>
</scene>

Is there anything wrong with how my XML is written? Additionally, to achieve accurate spectral results, do I need to make any further adjustments to the sensor or emitter settings?

mitsuba-renderer / mitsuba3

how to render in spectral mode correctly? #1180

Summary

Description