最新答案(我们知道它是错误的,正在等待正确的答案)
Photoshop 是一款非常古老且混乱的软件。关于为什么在执行从一种模式到另一种模式的转换时像素值会发生这样或那样的变化,没有清晰的文档说明。
您遇到的问题是因为当您将所选的 L* 通道转换为 Adobe Photoshop 中的 Greyscale 时,伽马值会发生变化。原生地,转换使用 1.74 的伽马值进行单通道到灰度转换。不要问我为什么,我猜这可能与旧激光打印机有关(?)。
无论如何,以下是我发现的最佳方法:
打开您的文件,将其转换为 LAB 模式,仅选择 L 通道
然后去:
编辑 > 转换颜色配置文件
您将选择“自定义伽马”并输入值 2.0(不要问我为什么 2.0 的效果更好,我不知道 Adobe 的软件制造商在想什么...)
此操作将使您的图片变成仅具有一个通道的灰度图像
然后您可以将其转换为 RGB 模式。
如果您将结果与自己的结果进行比较,您会看到差异高达4点多个百分点 - 所有差异都位于最暗的区域。
我怀疑这是因为伽马曲线应用不适用于LAB模式中的暗值(如您所知,所有低于0.008856的XYZ值在LAB中都是线性的)
结论:
据我所知,Adobe Photoshop中没有适当实现的方法可以从LAB模式提取L通道到灰度模式!
先前答案
这是我使用自己的方法得到的结果:
![RGB2LAB](https://istack.dev59.com/K7ftH.webp)
看起来与 Adobe Photoshop 的结果完全相同。
我不确定你的问题出在哪里,因为你描述的步骤与我所遵循的完全相同,也是我建议你遵循的步骤。我没有 Matlab,所以我使用了 Python:
import cv2, Syn
fn = "EASA2.png"
im = cv2.imread(fn,-1)
im = im[:,:,::-1]
XYZ = Syn.sRGB2XYZ(im)
WP_D65 = Syn.Yxy2XYZ((100,0.31271, 0.32902))
WP_D50 = Syn.Yxy2XYZ((100,0.34567, 0.35850))
XYZ2 = Syn.bradford_adaptation(XYZ, WP_D65, WP_D50)
LAB = Syn.XYZ2Lab(XYZ2, WP_D50)
L = LAB[:,:,0] /100. * 255.
cv2.imwrite("result.png", L)
Syn库是我自己的东西,这里是函数列表(抱歉有些凌乱):
def sRGB2XYZ(sRGB):
sRGB = np.array(sRGB)
aShape = np.array([1,1,1]).shape
anotherShape = np.array([[1,1,1],[1,1,1]]).shape
origShape = sRGB.shape
if sRGB.shape == aShape:
sRGB = np.reshape(sRGB, (1,1,3))
elif len(sRGB.shape) == len(anotherShape):
h,d = sRGB.shape
sRGB = np.reshape(sRGB, (1,h,d))
w,h,d = sRGB.shape
sRGB = np.reshape(sRGB, (w*h,d)).astype("float") / 255.
m1 = sRGB[:,0] > 0.04045
m1b = sRGB[:,0] <= 0.04045
m2 = sRGB[:,1] > 0.04045
m2b = sRGB[:,1] <= 0.04045
m3 = sRGB[:,2] > 0.04045
m3b = sRGB[:,2] <= 0.04045
sRGB[:,0][m1] = ((sRGB[:,0][m1] + 0.055 ) / 1.055 ) ** 2.4
sRGB[:,0][m1b] = sRGB[:,0][m1b] / 12.92
sRGB[:,1][m2] = ((sRGB[:,1][m2] + 0.055 ) / 1.055 ) ** 2.4
sRGB[:,1][m2b] = sRGB[:,1][m2b] / 12.92
sRGB[:,2][m3] = ((sRGB[:,2][m3] + 0.055 ) / 1.055 ) ** 2.4
sRGB[:,2][m3b] = sRGB[:,2][m3b] / 12.92
sRGB *= 100.
X = sRGB[:,0] * 0.4124 + sRGB[:,1] * 0.3576 + sRGB[:,2] * 0.1805
Y = sRGB[:,0] * 0.2126 + sRGB[:,1] * 0.7152 + sRGB[:,2] * 0.0722
Z = sRGB[:,0] * 0.0193 + sRGB[:,1] * 0.1192 + sRGB[:,2] * 0.9505
XYZ = np.zeros_like(sRGB)
XYZ[:,0] = X
XYZ[:,1] = Y
XYZ[:,2] = Z
XYZ = np.reshape(XYZ, origShape)
return XYZ
def Yxy2XYZ(Yxy):
Yxy = np.array(Yxy)
aShape = np.array([1,1,1]).shape
anotherShape = np.array([[1,1,1],[1,1,1]]).shape
origShape = Yxy.shape
if Yxy.shape == aShape:
Yxy = np.reshape(Yxy, (1,1,3))
elif len(Yxy.shape) == len(anotherShape):
h,d = Yxy.shape
Yxy = np.reshape(Yxy, (1,h,d))
w,h,d = Yxy.shape
Yxy = np.reshape(Yxy, (w*h,d)).astype("float")
XYZ = np.zeros_like(Yxy)
XYZ[:,0] = Yxy[:,1] * ( Yxy[:,0] / Yxy[:,2] )
XYZ[:,1] = Yxy[:,0]
XYZ[:,2] = ( 1 - Yxy[:,1] - Yxy[:,2] ) * ( Yxy[:,0] / Yxy[:,2] )
return np.reshape(XYZ, origShape)
def bradford_adaptation(XYZ, Neutral_source, Neutral_destination):
"""should be checked if it works properly, but it seems OK"""
XYZ = np.array(XYZ)
ashape = np.array([1,1,1]).shape
siVal = False
if XYZ.shape == ashape:
XYZ = np.reshape(XYZ, (1,1,3))
siVal = True
bradford = np.array(((0.8951000, 0.2664000, -0.1614000),
(-0.750200, 1.7135000, 0.0367000),
(0.0389000, -0.068500, 1.0296000)))
inv_bradford = np.array(((0.9869929, -0.1470543, 0.1599627),
(0.4323053, 0.5183603, 0.0492912),
(-.0085287, 0.0400428, 0.9684867)))
Xs,Ys,Zs = Neutral_source
s = np.array(((Xs),
(Ys),
(Zs)))
Xd,Yd,Zd = Neutral_destination
d = np.array(((Xd),
(Yd),
(Zd)))
source = np.dot(bradford, s)
Us,Vs,Ws = source[0], source[1], source[2]
destination = np.dot(bradford, d)
Ud,Vd,Wd = destination[0], destination[1], destination[2]
transformation = np.array(((Ud/Us, 0, 0),
(0, Vd/Vs, 0),
(0, 0, Wd/Ws)))
M = np.mat(inv_bradford)*np.mat(transformation)*np.mat(bradford)
w,h,d = XYZ.shape
result = np.dot(M,np.rot90(np.reshape(XYZ, (w*h,d)),-1))
result = np.rot90(result, 1)
result = np.reshape(np.array(result), (w,h,d))
if siVal == False:
return result
else:
return result[0,0]
def XYZ2Lab(XYZ, neutral):
"""transforms XYZ to CIE Lab
Neutral should be normalized to Y = 100"""
XYZ = np.array(XYZ)
aShape = np.array([1,1,1]).shape
anotherShape = np.array([[1,1,1],[1,1,1]]).shape
origShape = XYZ.shape
if XYZ.shape == aShape:
XYZ = np.reshape(XYZ, (1,1,3))
elif len(XYZ.shape) == len(anotherShape):
h,d = XYZ.shape
XYZ = np.reshape(XYZ, (1,h,d))
N_x, N_y, N_z = neutral
w,h,d = XYZ.shape
XYZ = np.reshape(XYZ, (w*h,d)).astype("float")
XYZ[:,0] = XYZ[:,0]/N_x
XYZ[:,1] = XYZ[:,1]/N_y
XYZ[:,2] = XYZ[:,2]/N_z
m1 = XYZ[:,0] > 0.008856
m1b = XYZ[:,0] <= 0.008856
m2 = XYZ[:,1] > 0.008856
m2b = XYZ[:,1] <= 0.008856
m3 = XYZ[:,2] > 0.008856
m3b = XYZ[:,2] <= 0.008856
XYZ[:,0][m1] = XYZ[:,0][XYZ[:,0] > 0.008856] ** (1/3.0)
XYZ[:,0][m1b] = ( 7.787 * XYZ[:,0][m1b] ) + ( 16 / 116.0 )
XYZ[:,1][m2] = XYZ[:,1][XYZ[:,1] > 0.008856] ** (1/3.0)
XYZ[:,1][m2b] = ( 7.787 * XYZ[:,1][m2b] ) + ( 16 / 116.0 )
XYZ[:,2][m3] = XYZ[:,2][XYZ[:,2] > 0.008856] ** (1/3.0)
XYZ[:,2][m3b] = ( 7.787 * XYZ[:,2][m3b] ) + ( 16 / 116.0 )
Lab = np.zeros_like(XYZ)
Lab[:,0] = (116. * XYZ[:,1] ) - 16.
Lab[:,1] = 500. * ( XYZ[:,0] - XYZ[:,1] )
Lab[:,2] = 200. * ( XYZ[:,1] - XYZ[:,2] )
return np.reshape(Lab, origShape)
rgb2lab
和类似的函数吗? - horchler