如何在opencv中读取透明像素的tif图像
我有一个具有透明像素的tif图像（我可以在paint.net中将它们看作透明像素）。
我正在尝试将它们读入openCV中的Mat中，并使用此代码：
Mat image=imread(imagePathname,CV_LOAD_IMAGE_UNCHANGED);
auto x=image.channels();
基于我的理解，由于输入图像具有透明度，所以channels（）应返回4，但返回3。
如何读取具有透明像素的tif图像并检查opencv中的像素是否透明？
EDIT1
运行imagemagick的结果：
Image: layer0003.tif
Format: TIFF (Tagged Image File Format)
Mime type: image/tiff
Class: DirectClass
Geometry: 10000x5000+0+0
Resolution: 150x150
Print size: 66.6667x33.3333
Units: PixelsPerInch
Type: TrueColorAlpha
Base type: TrueColor
Endianess: MSB
Colorspace: sRGB
Depth: 8-bit
Channel depth:
red: 8-bit
green: 8-bit
blue: 8-bit
alpha: 1-bit
Channel statistics:
Red:
min: 0 (0)
max: 255 (1)
mean: 23.6472 (0.0927342)
standard deviation: 37.6851 (0.147785)
kurtosis: 8.93054
skewness: 2.28009
Green:
min: 0 (0)
max: 255 (1)
mean: 22.8353 (0.0895504)
standard deviation: 37.6516 (0.147653)
kurtosis: 10.4255
skewness: 2.52881
Blue:
min: 0 (0)
max: 255 (1)
mean: 22.798 (0.0894041)
standard deviation: 37.6575 (0.147677)
kurtosis: 10.9059
skewness: 2.58999
Alpha:
min: 0 (0)
max: 255 (1)
mean: 89.055 (0.349235)
standard deviation: 121.566 (0.476728)
kurtosis: -1.59995
skewness: -0.632496
Image statistics:
Overall:
min: 0 (0)
max: 255 (1)
mean: 58.8064 (0.230613)
standard deviation: 68.9821 (0.270518)
kurtosis: 8.35337
skewness: 3.53852
Alpha: none #00000000
Rendering intent: Perceptual
Gamma: 0.454545
Chromaticity:
red primary: (0.64,0.33)
green primary: (0.3,0.6)
blue primary: (0.15,0.06)
white point: (0.3127,0.329)
Background color: white
Border color: srgba(223,223,223,1)
Matte color: grey74
Transparent color: none
Interlace: None
Intensity: Undefined
Compose: Over
Page geometry: 10000x5000+0+0
Dispose: Undefined
Iterations: 0
Compression: LZW
Orientation: TopLeft
Properties:
date:create: 2014-03-01T13:11:12+00:00
date:modify: 2014-02-28T17:48:41+00:00
signature: dfa3e35c35345ef3440ff15d15ad37222f9cf0376bed7b7710dd95f4e537e210
tiff:alpha: unassociated
tiff:endian: lsb
tiff:photometric: RGB
tiff:rows-per-strip: 1
tiff:timestamp: 2014:02:28 17:48:38
xmp:CreatorTool: Microsoft Windows Live Photo Gallery 15.4.3555.308
Profiles:
Profile-xmp: 12702 bytes
Artifacts:
filename: layer0003.tif
verbose: true
Tainted: False
Filesize: 20.42MB
Number pixels: 50M
Pixels per second: 60.24MB
User time: 0.827u
Elapsed time: 0:01.829
Version: ImageMagick 6.8.8-7 Q16 x64 2014-02-13 http://www.imagemagick.org
我只是有一段时间来重温这个:-)
基本上，我认为问题在于ImageMagick在编写输出文件时将采用最经济的文件大小。 所以，如果你的图像基本上是灰度的，但alpha（不透明度）通道只有0或1，ImageMagick会用16位灰度对数据和单位alpha通道进行编码。 我想这超出了OpenCV，因为它似乎期望alpha的编码与数据具有相同的深度。
所以，问题就变成了......“你如何强制组合你所需要的数据/ alpha（8位而不是8位加1位）灰度/颜色（8位灰度或8位颜色） ？”
可能还有其他方法，但现在我可以设想在图像底部添加一行，强制ImageMagick的手，并且在OpenCV中完成诀窍后，您可以很轻松地将其删除。
所以，让我们创建一个16位灰度图像，其中一个alpha位在中间形成方形透明孔：
convert -size 300x300 gradient:black-white -alpha set -region 100x100+100+100 -alpha transparent image.tif
让我们来看看我们有什么：
identify -verbose image.tif | head -14
Image: image.tif
Format: TIFF (Tagged Image File Format)
Mime type: image/tiff
Class: DirectClass
Geometry: 300x300+0+0
Units: PixelsPerInch
Type: GrayscaleAlpha
Base type: Grayscale
Endianess: LSB
Colorspace: Gray
Depth: 16-bit
Channel depth:
gray: 16-bit <--- 16-bit greyscale data
alpha: 1-bit <--- 1-bit alpha
现在让我们强制它到8位的alpha和8位数据：
# Force to at least 8-bit greyscale (but maybe RGB depending on rest of image) plus 8-bit alpha...
# ... by adding a line across the bottom with alpha varying from 0 to 1 (i=x coordinate,w=width)
convert image.tif
( +clone -resize x1! -channel A -fx "i/w" )
-append -depth 8 result.tif
让我们检查它的工作：
identify -verbose result.tif | head -16
Image: result.tif
Format: TIFF (Tagged Image File Format)
Mime type: image/tiff
Class: DirectClass
Geometry: 300x301+0+0 <--- one extra row
Units: PixelsPerInch
Type: GrayscaleAlpha
Base type: Grayscale
Endianess: LSB
Colorspace: Gray
Depth: 8-bit
Channel depth:
gray: 8-bit <--- 8-bit data
alpha: 8-bit <--- 8-bit alpha
现在让我们强制8位RGB加8位阿尔法：
# Force to 8-bit RGB plus 8-bit alpha...
# ... by adding a coloured line across the bottom with alpha varying from 0 to 1 (i=x coordinate,w=width)
convert image.tif
( +clone -resize x1! -channel RGBA -fx "rand()" )
-append -depth 8 result.tif
我们再来检查一下：
Image: result.tif
Format: TIFF (Tagged Image File Format)
Mime type: image/tiff
Class: DirectClass
Geometry: 300x301+0+0 <--- 1 extra row
Units: PixelsPerInch
Type: TrueColorAlpha
Base type: TrueColor <--- Truecolour
Endianess: LSB
Colorspace: sRGB <--- RGB
Depth: 8-bit
Channel depth:
red: 8-bit <--- 8-bit red
green: 8-bit <--- 8-bit green
blue: 8-bit <--- 8-bit blue
alpha: 8-bit <--- 8-bit alpha
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