van Hateren J H
Department of Biophysics, University of Groningen, The Netherlands.
Proc Biol Sci. 1993 Jan 22;251(1330):61-8. doi: 10.1098/rspb.1993.0009.
Fourier transforms of the spectral radiance of natural objects were investigated. The average spectral power spectrum Sc(fc) is well described by Sc(fc) = exp (-beta fc), with fc the spectral frequency (cycles micron-1), and beta = 0.419 +/- 0.097 microns. Average spectral contrast (Cc = [epsilon fc not equal to 0 Sc(fc)/Sc(0)]1/2) was 0.224 +/- 0.127. Optimal filters for colour pre-processing were derived using a recently developed theory of early vision (van Hateren (J. comp. Physiol. A 171, 157 (1992))). The theory assumes that the surrounding world is first sampled spatially, temporally and spectrally by an array of pre-filters, and subsequently filtered by an array of neural filters that maximize the information delivered to an array of noisy information channels. These optimal filters show lateral inhibition and spectral opponency for high signal-to-noise ratios (SNRs) and low temporal frequencies (ft). Decreasing SNR or increasing ft eventually produce filters that are spatially and spectrally low-pass, resulting in a visual system lacking lateral inhibition and spectral opponency. The optimal filters for high SNR lead to responses in the spectral channels approximately independent of the spectrum of the illumination, which is a first step towards colour constancy. Finally, the optimal spectral pre-filter has a half-width of about 100 nm; this is close to that of the common rhodopsins.
对自然物体光谱辐射率的傅里叶变换进行了研究。平均光谱功率谱Sc(fc) 可以很好地用Sc(fc) = exp (-βfc) 来描述，其中fc为光谱频率（每微米周期数），β = 0.419 ± 0.097微米。平均光谱对比度（Cc = [εfc≠0 Sc(fc)/Sc(0)]1/2）为0.224 ± 0.127。利用最近发展的早期视觉理论（范·哈泰伦（《计算生理学杂志A》171, 157 (1992)））推导了用于颜色预处理的最优滤波器。该理论假设周围世界首先由一组预滤波器在空间、时间和光谱上进行采样，随后由一组神经滤波器进行滤波，这些神经滤波器能使传递到一组有噪声信息通道的信息最大化。对于高信噪比（SNR）和低时间频率（ft），这些最优滤波器表现出侧向抑制和光谱对立性。信噪比降低或时间频率增加最终会产生在空间和光谱上为低通的滤波器，导致视觉系统缺乏侧向抑制和光谱对立性。高信噪比的最优滤波器会使光谱通道中的响应大致与照明光谱无关，这是迈向颜色恒常性的第一步。最后，最优光谱预滤波器的半高宽约为100纳米；这与常见视紫红质的半高宽相近。
