پردازش تصوير بين ‌دامنه‌اي با استفاده از تحليل تفكيك خطي و تطبيق دامنه مبتني ‌بر نمونه

Sample-oriented Domain Adaptation for Image Classification

پردازش تصوير روشي براي اعمال برخي عمليات­ه‌ا بر روي يك تصوير است به‌­طوري‌­كه با استفاده از آن، تصاويري با كيفيت بالاتر به­‌دست آمده يا برخي اطلاعات مفيد از تصوير استخراج مي­شود. الگوريتم­‌هاي سنتي پردازش تصوير در شرايطي­‌كه تصاوير آموزشي (دامنه منبع) كه براي ياددهي مدل استفاده مي­‌شوند، توزيع متفاوتي از تصاوير آزمايش (دامنه هدف) داشته باشند، نمي­‌توانند عملكرد خوبي داشته باشند. با اين‌حال، بسياري از برنامه‌هاي كاربردي دنياي واقعي به‌علت كمبود داده‌هاي برچسب‌دار آموزشي داراي محدوديت هستند؛ از‌اين‌رو از داده‌هاي برچسب‌دار دامنه‌هاي ديگر استفاده مي‌كنند. به‌اين ترتيب به‌خاطر اختلاف توزيع بين دامنه‌هاي منبع و هدف، طبقه‌بند يادگرفته شده براساس مجموعه آموزشي بر روي داده‌هاي آزمايشي عملكرد ضعيفي خواهد داشت. يادگيري انتقالي و انطباق دامنه، با به‌كارگيري مجموعه‌داده‌هاي موجود دو راه ‌حل برجسته براي مقابله با اين چالش هستند، و حتي با وجود اختلاف توزيع قابل ملاحظه بين دامنه‌ها مي‌توانند دانش را از دامنه‌هاي مرتبط به دامنه هدف انتقال دهند. فرض اصلي در مسأله تغيير دامنه اين است كه توزيع حاشيه‌اي يا توزيع شرطي داده‌هاي منبع و هدف متفاوت باشد. تطبيق دامنه به‌طور صريح با استفاده از معيار فاصله ازپيش تعيين‌شده تفاوت در توزيع حاشيه‌اي، توزيع شرطي يا هر دو توزيع را كاهش مي‌دهد. در اين مقاله، ما به يك سناريوي چالش‌برانگيز مي‌پردازيم كه در آن تصاوير دامنه‌هاي منبع و هدف در توزيع‌هاي حاشيه‌اي متفاوت بوده و تصاوير هدف داراي برچسب نيستند. بيش‌تر روش‌هاي قبلي دو استراتژي يادگيري تطابق ويژگي‌ها و وزن‌دهي مجدد نمونه‌ها را به‌طور مستقل براي تطبيق دامنه‌ها مورد بررسي قرار داده‌اند. در اين مقاله، ما نشان مي‌دهيم زماني كه تفاوت دامنه‌ها به‌طور قابل توجهي بزرگ باشد، هر دو استراتژي مهم و اجتناب‌ناپذير هستند. روش پيشنهادي ما تحت عنوان تطبيق دامنه مبتني‌بر نمونه براي طبقه‌بندي تصاوير (DAIC)، يك فرايند كاهش بُعد بوده كه با كاهش اختلاف توزيع تصاوير آموزشي و آزمايشي و به‌كارگيري هم‌زمان تطابق ويژگي‌ها و وزن‌دهي مجدد كارايي مدل را افزايش مي‌دهد. ما با گسترش واگرايي برگمن غيرخطي براي اندازه‌گيري تفاوت توزيع حاشيه‌اي و اعمال آن به الگوريتم كاهش بعد آناليز تفكيك خطي فيشر، از آن براي ساخت يك نمايش ويژگي مؤثر و قوي براي تفاوت‌هاي توزيع قابل ملاحظه بين دامنه‌ها استفاده مي‌كنيم؛ همچنين، DAIC از مزيت برچسب‌گذاري اوليه براي داده‌هاي هدف به‌صورت تكرار‌شونده براي هم‌گرايي مدل استفاده مي‌كند. آزمايش‌هاي گسترده ما نشان مي‌دهد كه DAIC به ‌طور قابل توجهي بهتر از الگوريتم‌هاي يادگيري ماشين پايه و ديگر روش‌هاي يادگيري انتقالي در نُه مجموعه داده‌ بصري تحت سناريوهاي مختلف عمل مي‌كند.

Image processing is a method to perform some operations on an image, in order to get an enhanced image or to extract some useful information from it. The conventional image processing algorithms cannot perform well in scenarios where the training images (source domain) that are used to learn the model have a different distribution with test images (target domain). Also, many real world applications suffer from a limited number of training labeled data and therefore benefit from the related available labeled datasets to train the model. In this way, since there is the distribution difference across the source and target domains (domain shift problem), the learned classifier on the training set might perform poorly on the test set. Transfer learning and domain adaptation are two outstanding solutions to tackle this challenge by employing available datasets, even with significant difference in distribution and properties, to transfer the knowledge from a related domain to the target domain. The main assumption in domain shift problem is that the marginal or the conditional distribution of the source and the target data is different. Distribution adaptation explicitly minimizes predefined distance measures to reduce the difference in the marginal distribution, conditional distribution, or both. In this paper, we address a challenging scenario in which the source and target domains are different in marginal distributions, and the target images have no labeled data. Most prior works have explored two following learning strategies independently for adapting domains: feature matching and instance reweighting. In the instance reweighting approach, samples in the source data are weighted individually so that the distribution of the weighted source data is aligned to that of the target data. Then, a classifier is trained on the weighted source data. This approach can effectively eliminate unrelated source samples to the target data, but it would reduce the number of samples in adapted source data, which results in an increase in generalization errors of the trained classifier. Conversely, the feature-transform approach creates a feature map such that distributions of both datasets are aligned while both datasets are well distributed in the transformed feature space. In this paper, we show that both strategies are important and inevitable when the domain difference is substantially large. Our proposed using sample-oriented Domain Adaptation for Image Classification (DAIC) aims to reduce the domain difference by jointly matching the features and reweighting the instances across images in a principled dimensionality reduction procedure, and construct new feature representation that is invariant to both the distribution difference and the irrelevant instances. We extend the nonlinear Bregman divergence to measure the difference in marginal, and integrate it with Fisher’s linear discriminant analysis (FLDA) to construct feature representation that is effective and robust for substantial distribution difference. DAIC benefits pseudo labels of target data in an iterative manner to converge the model. We consider three types of cross-domain image classification data, which are widely used to evaluate the visual domain adaptation algorithms: object (Office+Caltech- 256), face (PIE) and digit (USPS, MNIST). We use all three datasets prepared by and construct 34 cross-domain problems. The Office-Caltech-256 dataset is a benchmark dataset for cross-domain object recognition tasks, which contains 10 overlapping categories from following four domains: Amazon (A), Webcam (W), DSLR (D) and Caltech256 (C). Therefore 4 × 3 = 12 cross domain adaptation tasks are constructed, namely A → W, ..., C → D. USPS (U) and MNIST (M) datasets are widely used in computer vision and pattern recognition tasks. We conduct two handwriting recognition tasks, i.e., usps-mnist and mnist-usps. PIE is a benchmark dataset for face detection task and has 41,368 face images of size 3232 from 68 individuals. The images were taken by 13 synchronized cameras and 21 flashes, under varying poses, illuminations, and expressions. PIE dataset consists five subsets depending on the different poses as follows: PIE1 (C05, left pose), PIE2 (C07, upward pose), PIE3 (C09, downward pose), PIE4 (C27, frontal pose), PIE5 (C29, right pose). Thus, we can construct 20 cross domain problems, i.e., P1 → P2, P1 → P3, ..., P5 → P4. We compare our proposed DAIC with two baseline machine learning methods, i.e., NN, Fisher linear discriminant analysis (FLDA) and nine state-of-the-art domain adaptation methods for image classification problems (TSL, DAM, TJM, FIDOS and LRSR). Due to these methods are considered as dimensionality reduction approaches, we train a classifier on the labeled training data (e.g., NN classifier), and then apply it on test data to predict the labels of the unlabeled target data. DAIC efficiently preserves and utilizes the specific information among the samples from different domains. The obtained results indicate that DAIC outperforms several state of-the-art adaptation methods even if the distribution difference is substantially large.