『计算机视觉』imgaug图像增强库中部分API简介
https://github.com/aleju/imgaug
介绍一下官方demo中用到的几个变换,工程README.md已经给出了API简介,个人觉得不好理解,特此单独记录一下:
import numpy as np import imgaug as ia import imgaug.augmenters as iaa # random example images images = np.random.randint(0, 255, (16, 128, 128, 3), dtype=np.uint8) # Sometimes(0.5, ...) applies the given augmenter in 50% of all cases, # e.g. Sometimes(0.5, GaussianBlur(0.3)) would blur roughly every second image. sometimes = lambda aug: iaa.Sometimes(0.5, aug) # Define our sequence of augmentation steps that will be applied to every image # All augmenters with per_channel=0.5 will sample one value _per image_ # in 50% of all cases. In all other cases they will sample new values # _per channel_. seq = iaa.Sequential( [ # apply the following augmenters to most images iaa.Fliplr(0.5), # horizontally flip 50% of all images iaa.Flipud(0.2), # vertically flip 20% of all images # crop images by -5% to 10% of their height/width sometimes(iaa.CropAndPad( percent=(-0.05, 0.1), pad_mode=ia.ALL, pad_cval=(0, 255) )), sometimes(iaa.Affine( scale={"x": (0.8, 1.2), "y": (0.8, 1.2)}, # scale images to 80-120% of their size, individually per axis translate_percent={"x": (-0.2, 0.2), "y": (-0.2, 0.2)}, # translate by -20 to +20 percent (per axis) rotate=(-45, 45), # rotate by -45 to +45 degrees shear=(-16, 16), # shear by -16 to +16 degrees order=[0, 1], # use nearest neighbour or bilinear interpolation (fast) cval=(0, 255), # if mode is constant, use a cval between 0 and 255 mode=ia.ALL # use any of scikit-image's warping modes (see 2nd image from the top for examples) )), # execute 0 to 5 of the following (less important) augmenters per image # don't execute all of them, as that would often be way too strong iaa.SomeOf((0, 5), [ sometimes(iaa.Superpixels(p_replace=(0, 1.0), n_segments=(20, 200))), # convert images into their superpixel representation iaa.OneOf([ iaa.GaussianBlur((0, 3.0)), # blur images with a sigma between 0 and 3.0 iaa.AverageBlur(k=(2, 7)), # blur image using local means with kernel sizes between 2 and 7 iaa.MedianBlur(k=(3, 11)), # blur image using local medians with kernel sizes between 2 and 7 ]), iaa.Sharpen(alpha=(0, 1.0), lightness=(0.75, 1.5)), # sharpen images iaa.Emboss(alpha=(0, 1.0), strength=(0, 2.0)), # emboss images # search either for all edges or for directed edges, # blend the result with the original image using a blobby mask iaa.SimplexNoiseAlpha(iaa.OneOf([ iaa.EdgeDetect(alpha=(0.5, 1.0)), iaa.DirectedEdgeDetect(alpha=(0.5, 1.0), direction=(0.0, 1.0)), ])), iaa.AdditiveGaussianNoise(loc=0, scale=(0.0, 0.05*255), per_channel=0.5), # add gaussian noise to images iaa.OneOf([ iaa.Dropout((0.01, 0.1), per_channel=0.5), # randomly remove up to 10% of the pixels iaa.CoarseDropout((0.03, 0.15), size_percent=(0.02, 0.05), per_channel=0.2), ]), iaa.Invert(0.05, per_channel=True), # invert color channels iaa.Add((-10, 10), per_channel=0.5), # change brightness of images (by -10 to 10 of original value) iaa.AddToHueAndSaturation((-20, 20)), # change hue and saturation # either change the brightness of the whole image (sometimes # per channel) or change the brightness of subareas iaa.OneOf([ iaa.Multiply((0.5, 1.5), per_channel=0.5), iaa.FrequencyNoiseAlpha( exponent=(-4, 0), first=iaa.Multiply((0.5, 1.5), per_channel=True), second=iaa.ContrastNormalization((0.5, 2.0)) ) ]), iaa.ContrastNormalization((0.5, 2.0), per_channel=0.5), # improve or worsen the contrast iaa.Grayscale(alpha=(0.0, 1.0)), sometimes(iaa.ElasticTransformation(alpha=(0.5, 3.5), sigma=0.25)), # move pixels locally around (with random strengths) sometimes(iaa.PiecewiseAffine(scale=(0.01, 0.05))), # sometimes move parts of the image around sometimes(iaa.PerspectiveTransform(scale=(0.01, 0.1))) ], random_order=True ) ], random_order=True ) images_aug = seq.augment_images(images)
Superpixels:生成随机数量的超像素区域,对原图进行替换,直观效果是原图部分区域变得模糊
各种blur:模糊,对应几种滤波操作
sharp:字面意思,锐化
emboss:压印浮凸字体(或图案); 凹凸印
EdgeDetect:边缘检测
DirectedEdgeDetect:边缘检测,只检测某些方向的,直观来看和上面的比检测出来的数目会少很多
DropOut:随机丢弃像素
CoarseDropout:随机丢弃某位置某通道像素
Invert:有一定几率将batch中的图片像素取反(或者特定通道取反)
Add:像素值成比例增加/减小(特指亮度)
AddToHueAndSaturation:增加色相、饱和度
Multiply:每个像素随机乘一个数(各不相图),造成局部变亮、局部变暗
ContrastNormalization:调整对比度,0.5表示和128的差值部分会处以2降低对比度
FrequencyNoiseAlpha:参数需要两个增强函数,本函数会混合两个增强函数增强后的结果
Grayscale:灰度图和原图的混合(1意味着全灰度)