## 常用操作

Modifies in-place,Preserves aspect ratio
>>> myImage.thumbnail ((128, 128), Image.ANTIALIAS)

>>> bounds = (100, 100, 400, 400)
>>> cutoutIm = myImage.crop (bounds)

rotated around its center

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)

1 Image.open(f)

>>> import Image

>>>

>>> Im = Image.open("lena.jpg")

>>> print Im.mode,Im.size,Im.format

RGB (256, 256) JPEG

>>> Im.show()

2 Image.new(mode,size,color=None)

color的默认值是黑色，这里我们新建一个红色的图像。

>>> newIm = Image.new (“RGBA”, (640, 480), (255, 0, 0)) #新建一个image对象creating images from scratch

3 Image.blend(i1,i2,a)  -- (p1 x (1 - a) + p2 x a)

>>> Im2 = Image.open("background.jpg").convert(Im.mode)

>>> Im2 = Im2.resize(Im.size)

>>> Im2.show()

>>>

>>> img = Image.blend(Im,Im2,0.2)

>>> img.show()

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

 save(f,format=None) 保存 如果f是一个file对象，必须指定format（format codes） convert(mode) 转换mode copy() crop(bbox) 剪切 原图中bbox区域 filter(name) 滤镜 the name of predefined image enhancement filters滤镜名字需要import ImageFilter getbands() 通道的字符串序列 如RGB图返回('R', 'G', 'B') getbbox() 包含非零区域的最小bbox getextrema() 最大最小像素点值 min&max pixel value单通道图：返回元组(min,max)多通道图：返回各个通道的元组组成的元组 getpixel(xy) 取像素点值 坐标xy处的pixel value or a sequence of pixel values histogram(mask=None) 统计直方图 单通道图：返回列表[c0, c1, ...]，ci是值为i的像素数 多通道图：a single sequence that is the concatenation of the sequences for all bands mask参数: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) 粘贴图片 where参数可以是1 (x,y)坐标对：i2的像素点(0,0)对齐原图中的(x,y)粘贴，i2超过原图边界的部分被抛弃2 bbox：i2必须和该bounding box大小一致3 None：i2必须和原图大小一致如果i2的mode和原图不一致，粘贴前会被转换。mask参数：a same-sized mask image of mode "1","L" or “RGBA ”(control which pixels get replaced) paste(color,box=None,mask=None) 填充颜色 如果box省略，整个图被填充为color色；mask参数同上 point(function) 改变像素点(函数) Returns a new image with each pixel modified. point(table) 改变像素点(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) 改变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) 改变单个像素点颜色 Note that this method is relatively slow. For more extensive changes, use paste or the ImageDraw module instead. resize(size,filter=None) 调整大小 rotate(theta) 旋转（围绕图片中心） Any pixels that are not covered by rotation of the original image are set to black. show() 显示图片 On Unix systems, this method runs the xv image viewer to display the image. On Windows boxes,the image is saved in BMP format and can be viewed using Paint. This can be useful for debugging. split() 分离通道 返回各个通道的灰度图组成的元组Returns a tuple containing each band of the original image as an image of mode "L". For example, applying this method to an "RGB" image produces a tuple of three images, one each for the red, green, and blue bands. thumbnail(size,filter=None) 缩略图 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变换 The values a through f are the first two rows of an affine transform matrix.Each pixel at (x,y) in the resulting image comes from position (ax+by+c,dx+ey+f) in the inputimage, rounded to the nearest pixel. transpose(method) 翻转旋转 ROTATE_90/180/270(clockwise), FLIP_TOP_BOTTOM(horizontal), FLIP_RIGHT_LEFT(vertical)

## The ImageDraw Module

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.

import Image, ImageDraw

im = Image.open(“vacation.jpeg")
drawSurface = ImageDraw.Draw(im)

• 弧/弦/扇形 chord arc pieslice (bbox, strtAng, endAng)
• 椭圆 ellipse (bbox)
• 线段/多段线 line (L)  draw.line(((60,60),(90,60), (90,90), (60,90), (60,60))) #draw a square
• 点 point (xy)  #单像素点很小看不清,实际中可用实心小圆代替
• 多边形 polygon (L) draw.polygon([(60,60), (90,60), (90,90), (60,90)]) #draw a square
• 矩形 rectangle (bbox)       # first coord属于矩形, second coord不属于
• 文字 text(xy,message,font=None) 绘制文字message，文本区域左上角坐标为xy
drawable.text((10, 10), "Hello", fill=(255,0,0), font=None)
• 文字大小 textsize(message,font=None)  给定文字message，返回所占像素(width,height)

• fill=fillColor
• outline=outlineColor

import ImageFont

ttFont = ImageFont.truetype (“arial.ttf”, 16)

drawable.text ((10, 10), “Hello”, fill=(255,0,0), font=ttFont)

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 图像合成, algorithmic painting 算法绘画, and more.

At this time, channel operations are only implemented for 8-bit images (e.g. "L" and "RGB").

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]))

posted on 2012-04-19 10:59 小唯THU 阅读(...) 评论(...) 编辑 收藏

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