常用操作
合成 Image.blend(i1,i2,a)/Image.composite(i1,i2,mask)
縮略圖 thumbnail(size,filter=None)
Modifies in-place,Preserves aspect ratio
>>> myImage.thumbnail ((128, 128), Image.ANTIALIAS)
剪切 crop(bbox)
>>> bounds = (100, 100, 400, 400)
>>> cutoutIm = myImage.crop (bounds)
粘貼 paste(i2,where,mask=None)/paste(color,box=None,mask=None)
旋轉 rotate(theta)
rotated around its center
翻轉旋轉 transpose(method)
ROTATE_90/180/270(clockwise), FLIP_TOP_BOTTOM(horizontal), FLIP_RIGHT_LEFT(vertical)
>>> fixedIm = myImage.transpose (ROTATE_90)
The Image Module
The Image module provides
- a class with the same name which is used to represent a PIL image.
- The module also provides a number of factory functions(including functions to load images from files, and to create new images)
圖像對象 Image – from file or newly created
所有的圖片操作必須有一個操作對象，例如Pil提供open(filename)進行這個過程，此後，一切關於圖片的操作均基於這個對象。有以下幾種創建image對象的方式：
1 Image.open(f)
>>> import Image
>>>
>>> Im = Image.open("lena.jpg")
>>> print Im.mode,Im.size,Im.format
RGB (256, 256) JPEG
>>> Im.show()
如果文件不能打開，會拋出IOError異常。
可以查看image對象的format,mode,size,palette,info幾個屬性。
調用im.show()會在圖片查看工具中顯示當前操作的image對象。
標準版本的show方法的實現不太高效，因爲它先把image保存到一個臨時文件，然後調用xy工具來顯示圖像。如果你沒有安裝xy，那麼它就無法工作了。不過如果它可以工作，倒還是非常方便用來debug和測試。
2 Image.new(mode,size,color=None)
color的默認值是黑色，這裏我們新建一個紅色的圖像。
>>> newIm = Image.new (“RGBA”, (640, 480), (255, 0, 0)) #新建一個image對象creating images from scratch
3 Image.blend(i1,i2,a) -- (p1 x (1 - a) + p2 x a)
選一張灰度圖(L)做背景，和雷娜圖(RGB)做blend操作
>>> Im2 = Image.open("background.jpg").convert(Im.mode)
>>> Im2 = Im2.resize(Im.size)
>>> Im2.show()
>>>
>>> img = Image.blend(Im,Im2,0.2)
>>> img.show()
操作完畢後save(filename)用以保存這個臨時的image對象img到硬盤。
4 Image.composite(i1,i2,mask) --equal-sized images i1 ,i2 and mask("1", "L", or "RGBA") (p1 x (1 - m) + p2 x m)
5 Image.eval(f,i) -- applying a function f to each pixel of image i
6 Image.merge(mode,bandList) --Creates a multi-band image from a sequence of single-band images of equal size
以下是Image對象的全部方法：
| save(f,format=None) | 保存 | 如果f是一個file對象，必須指定format（format codes） |
| convert(mode) | 轉換mode | |
| copy() | ||
| crop(bbox) | 剪切 | 原圖中bbox區域 |
| filter(name) | 濾鏡 | the name of predefined image enhancement filters 濾鏡名字需要import ImageFilter |
| getbands() | 通道的字符串序列 | 如RGB圖返回('R', 'G', 'B') |
| getbbox() | 包含非零區域的最小bbox | |
| getextrema() | 最大最小像素點值 | min&max pixel value 單通道圖：返回元組(min,max) 多通道圖：返回各個通道的元組組成的元組 |
| getpixel(xy) | 取像素點值 | 座標xy處的pixel value or a sequence of pixel values |
| histogram(mask=None) |
統計直方圖 |
單通道圖：返回列表[c0, c1, ...]，ci是值爲i的像素數 多通道圖：a single sequence that is the concatenation of the sequences for all bands mask參數:a same-sized mask image of mode "1" or "L"(include only those pixels correspond to nonzero pixels in the mask argument) |
| offset(dx,dy=None) |
平移 |
Returns a new image the same size as the original, but with all pixels rotated dx in the +x direction,and dy in the +y direction. If dy is omitted, it defaults to the same value as dx. |
| paste(i2,where,mask=None) | 粘貼圖片 | where參數可以是 1 (x,y)座標對：i2的像素點(0,0)對齊原圖中的(x,y)粘貼，i2超過原圖邊界的部分被拋棄 2 bbox：i2必須和該bounding box大小一致 3 None：i2必須和原圖大小一致 如果i2的mode和原圖不一致，粘貼前會被轉換。 mask參數：a same-sized mask image of mode "1","L" or “RGBA ”(control which pixels get replaced) |
| paste(color,box=None,mask=None) | 填充顏色 | 如果box省略，整個圖被填充爲color色；mask參數同上 |
| point(function) | 改變像素點(函數) | Returns a new image with each pixel modified. |
| point(table) | 改變像素點(查表) | To translate pixels using a table(a sequence of 256n values, where n is the number of bands in the image) lookup |
| putalpha(band) |
改變alpha通道 |
The pixels of the band image(same-sized,"L" or "1") replace the alpha band(A) of the original image(RGBA) in place. |
| putpixel(xy, color) | 改變單個像素點顏色 | Note that this method is relatively slow. For more extensive changes, use paste or the ImageDraw module instead. |
| resize(size,filter=None) | 調整大小 | |
| rotate(theta) |
旋轉（圍繞圖片中心） |
Any pixels that are not covered by rotation of the original image are set to black. |
| show() |
顯示圖片 |
On Unix systems, this method runs the xv image viewer to display the image. |
| split() |
分離通道 |
返回各個通道的灰度圖組成的元組 |
| thumbnail(size,filter=None) | 縮略圖 | Modifies in-place,Preserves aspect ratio |
| transform(xs, ys, Image.EXTENT, (x0,y0,x1,y1)) |
Returns a transformed copy of the image. In the transformed image, the point originally at (x0,y0) will appear at (0,0), and point (x1,y1) will appear at (xs, ys). |
|
| transform(xs, ys, Image.AFFINE, (a,b,c,d,e,f)) | affine變換 |
The values a through f are the first two rows of an affine transform matrix. |
| transpose(method) | 翻轉旋轉 | ROTATE_90/180/270(clockwise), FLIP_TOP_BOTTOM(horizontal), FLIP_RIGHT_LEFT(vertical) |
The ImageDraw Module
支持2D圖像 The ImageDraw module provide basic 2D graphics support for Image objects.
It can for example be used to
- create new images,
- annotate or retouch existing images, and to generate graphics on the fly for web use.
For a more advanced drawing library for PIL, see The aggdraw Module.
創建繪畫對象 ImageDraw module creates drawing surface for image
import Image, ImageDraw
im = Image.open(“vacation.jpeg")
drawSurface = ImageDraw.Draw(im)
基本繪畫操作 Basic methods of drawing surface
- 弧/弦/扇形 chord arc pieslice (bbox, strtAng, endAng)
- 橢圓 ellipse (bbox)
- 線段/多段線 line (L) draw.line(((60,60),(90,60), (90,90), (60,90), (60,60))) #draw a square
- 點 point (xy) #單像素點很小看不清,實際中可用實心小圓代替
- 多邊形 polygon (L) draw.polygon([(60,60), (90,60), (90,90), (60,90)]) #draw a square
- 矩形 rectangle (bbox) # first coord屬於矩形, second coord不屬於
- 文字 text(xy,message,font=None) 繪製文字message，文本區域左上角座標爲xy
drawable.text((10, 10), "Hello", fill=(255,0,0), font=None) - 文字大小 textsize(message,font=None) 給定文字message，返回所佔像素(width,height)
可選參數 Common optional args for these methods
- fill=fillColor
- outline=outlineColor
矢量字體支持 TrueType Font support
import ImageFont
ttFont = ImageFont.truetype (“arial.ttf”, 16)
drawable.text ((10, 10), “Hello”, fill=(255,0,0), font=ttFont)
例子：Draw a Grey Cross Over an Image
import Image, ImageDraw im = Image.open("lena.pgm") # Creates an object that can be used to draw in the given image. draw = ImageDraw.Draw(im) # draw.line(xy, options) => Draws a line between the coordinates in the xy list. # The coordinate list can be any sequence object containing either 2-tuples [ (x, y), ... ] # or numeric values [ x, y, ... ]. # The fill option gives the color to use for the line. draw.line((0, 0) + im.size, fill=128) draw.line((0, im.size[1], im.size[0], 0), fill=128) del draw # write to stdout im.save(sys.stdout, "PNG")
The ImageChops module
a number of arithmetical image operations, called channel operations ("chops" 通道操作).
These can be used for various purposes, including special effects 特殊效果, image compositions 圖像合成, algorithmic painting 算法繪畫, and more.
At this time, channel operations are only implemented for 8-bit images (e.g. "L" and "RGB").
例子:比較兩幅圖像
Exact Comparison：
The quickest way to determine if two images have exactly the same contents is to get the difference between the two images, and then calculate the bounding box of the non-zero regions in this image. If the images are identical, all pixels in the difference image are zero, and the bounding box function returns None.
import ImageChops def equal(im1, im2): return ImageChops.difference(im1, im2).getbbox() is None
To get a measure of how similar two images are, you can calculate the root-mean-square (RMS) value of the difference between the images. If the images are exactly identical, this value is zero. The following function uses the difference function, and then calculates the RMS value from the histogram of the resulting image.
RMS Difference：
To get a measure of how similar two images are, you can calculate the root-mean-square (RMS) value of the difference between the images. If the images are exactly identical, this value is zero. The following function uses the difference function, and then calculates the RMS value from the histogram of the resulting image.
# Example: File: imagediff.py import ImageChops import math, operator def rmsdiff(im1, im2): "Calculate the root-mean-square difference between two images" h = ImageChops.difference(im1, im2).histogram() # calculate rms return math.sqrt(reduce(operator.add, map(lambda h, i: h*(i**2), h, range(256)) ) / (float(im1.size[0]) * im1.size[1]))
本文轉自:http://www.cnblogs.com/wei-li/archive/2012/04/19/2456725.html