[Image-SIG] Auto level with PIL?

[Fredrik Lundh]

Chris Barker wrote:

> I need to do something like Photoshop's Auto Level to a bunch of images.
> Honestly, I have only a vague idea of what it does, but I saw that
> someone posted a script to do it here about 6 years ago, but I can't
> seem to get that code from the list archives.

this one?

http://aspn.activestate.com/ASPN/Mail/Message/image-sig/582729

here's the code from that post:

# adjust levels to fill histogram
# Kevin Cazabon, 1999.  kcazabon at rogers.wave.ca  kcaza at cymbolic.com

def levels(data, all_same = 0, clip = 0):

    if data.mode not in ['RGB', 'CMYK']:
        return data

    lut = makelut(data, all_same, clip)

    data = data.point(lut)

    return data

def find_hi_lo(lut, clip):
    min = None
    max = None

    for i in range(len(lut)):
        if lut[i] > clip:
            min = i
            break

    lut.reverse()

    for i in range(len(lut)):
        if lut[i] > clip:
            max = 255 - i
            break

    return min, max

def scale(channels, min, max):
    lut = []
    for i in range (channels):
        for i in range(256):
            value = int((i - min)*(255.0/float(max-min)))
            if value < 0:
                value = 0
            if value > 255:
                value = 255
            lut.append(value)

    return lut


def makelut(data, all_same, clip):
    import Image

    histogram = data.histogram()

    lut = []
    r, g, b, k = [], [], [], []

    channels = len(histogram)/256

    for i in range(256):
        r.append(histogram[i])
        g.append(histogram[256+i])
        b.append(histogram[512+i])
    if channels == 4:
        for i in range(256):
            k.append(histogram[768+i])


    rmin, rmax = find_hi_lo(r, clip)
    gmin, gmax = find_hi_lo(g, clip)
    bmin, bmax = find_hi_lo(b, clip)
    if channels == 4:
        kmin, kmax = find_hi_lo(k)
    else:
        kmin, kmax = 128, 128

    if all_same == 1:

        min_max = [rmin, gmin, bmin, kmin, rmax, gmax, bmax, kmax]
        min_max.sort()
        lut = scale(channels, min_max[0], min_max[-1])

    else:

        r_lut = scale(1, rmin, rmax)
        g_lut = scale(1, gmin, gmax)
        b_lut = scale(1, bmin, bmax)
        if channels == 4:
            k_lut = scale(1, kmin, kmax)

        lut = []

        for i in range (256):
            lut.append(r_lut[i])
        for i in range (256):
            lut.append(g_lut[i])
        for i in range (256):
            lut.append(b_lut[i])
        if channels == 4:
            for i in range (256):
                lut.append(k_lut[i])

    return lut