Researcher:
Korkmaz, Cansu

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Cansu

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Korkmaz

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Korkmaz, Cansu

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2021 - 20224

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Researcher Of Publications: search.filters.isAuthorOfPublication.e56f4589-b809-4e57-bcc7-2b4668e64e7b

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    Perception-distortion trade-off in the SR space spanned by flow models
    (The Institute of Electrical and Electronics Engineers Signal Processing Society, 2022) Erdem, Erkut; Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; Department of Computer Engineering; Doğan, Zafer; Tekalp, Ahmet Murat; Erdem, Aykut; Korkmaz, Cansu; Faculty Member; Faculty Member; Faculty Member; PhD Student; Department of Electrical and Electronics Engineering; Department of Computer Engineering; Koç Üniversitesi İş Bankası Yapay Zeka Uygulama ve Araştırma Merkezi (KUIS AI)/ Koç University İş Bank Artificial Intelligence Center (KUIS AI); College of Engineering; College of Engineering; College of Engineering; Graduate School of Sciences and Engineering; 280658; 26207; 20331; N/A
    Flow-based generative super-resolution (SR) models learn to produce a diverse set of feasible SR solutions, called the SR space. Diversity of SR solutions increases with the temperature (τ) of latent variables, which introduces random variations of texture among sample solutions, resulting in visual artifacts and low fidelity. In this paper, we present a simple but effective image ensembling/fusion approach to obtain a single SR image eliminating random artifacts and improving fidelity without significantly compromising perceptual quality. We achieve this by benefiting from a diverse set of feasible photo-realistic solutions in the SR space spanned by flow models. We propose different image ensembling and fusion strategies which offer multiple paths to move sample solutions in the SR space to more desired destinations in the perception-distortion plane in a controllable manner depending on the fidelity vs. perceptual quality requirements of the task at hand. Experimental results demonstrate that our image ensembling/fusion strategy achieves more promising perception-distortion tradeoff compared to sample SR images produced by flow models and adversarially trained models in terms of both quantitative metrics and visual quality. © 2022 IEEE.
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    MMSR: Multiple-model learned image super-resolution benefiting from class-specific image priors
    (The Institute of Electrical and Electronics Engineers Signal Processing Society, 2022) Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; Doğan, Zafer; Tekalp, Ahmet Murat; Korkmaz, Cansu; Faculty Member; Faculty Member; PhD Student; Department of Electrical and Electronics Engineering; College of Engineering; College of Engineering; Graduate School of Sciences and Engineering; 280658; 26207; N/A
    Assuming a known degradation model, the performance of a learned image super-resolution (SR) model depends on how well the variety of image characteristics within the training set matches those in the test set. As a result, the performance of an SR model varies noticeably from image to image over a test set depending on whether characteristics of specific images are similar to those in the training set or not. Hence, in general, a single SR model cannot generalize well enough for all types of image content. In this work, we show that training multiple SR models for different classes of images (e.g., for text, texture, etc.) to exploit class-specific image priors and employing a post-processing network that learns how to best fuse the outputs produced by these multiple SR models surpasses the performance of state-of-the-art generic SR models. Experimental results clearly demonstrate that the proposed multiple-model SR (MMSR) approach significantly outperforms a single pre-trained state-of-the-art SR model both quantitatively and visually. It even exceeds the performance of the best single class-specific SR model trained on similar text or texture images. © 2022 IEEE.
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    PublicationOpen Access
    On the computation of PSNR for a set of images or video
    (Institute of Electrical and Electronics Engineers (IEEE), 2021) Department of Electrical and Electronics Engineering; Doğan, Zafer; Tekalp, Ahmet Murat; Keleş, Onur; Yılmaz, Mustafa Akın; Korkmaz, Cansu; Faculty Member; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; Graduate School of Sciences and Engineering; 280658; 26207; N/A; N/A; N/A
    When comparing learned image/video restoration and compression methods, it is common to report peak-signal to noise ratio (PSNR) results. However, there does not exist a generally agreed upon practice to compute PSNR for sets of images or video. Some authors report average of individual image/frame PSNR, which is equivalent to computing a single PSNR from the geometric mean of individual image/frame mean-square error (MSE). Others compute a single PSNR from the arithmetic mean of frame MSEs for each video. Furthermore, some compute the MSE/PSNR of Y-channel only, while others compute MSE/PSNR for RGB channels. This paper investigates different approaches to computing PSNR for sets of images, single video, and sets of video and the relation between them. We show the difference between computing the PSNR based on arithmetic vs. geometric mean of MSE depends on the distribution of MSE over the set of images or video, and that this distribution is task-dependent. In particular, these two methods yield larger differences in restoration problems, where the MSE is exponentially distributed and smaller differences in compression problems, where the MSE distribution is narrower. We hope this paper will motivate the community to clearly describe how they compute reported PSNR values to enable consistent comparison.
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    PublicationOpen Access
    Two stage domain adapted training for better generalization in real-world image restoration and super resolution
    (Institute of Electrical and Electronics Engineers (IEEE), 2021) Department of Electrical and Electronics Engineering; Tekalp, Ahmet Murat; Korkmaz, Cansu; Doğan, Zafer; Faculty Member; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; Graduate School of Sciences and Engineering; 26207; N/A; 280658
    It is well-known that in inverse problems, end-to-end trained networks overfit the degradation model seen in the training set, i.e., they do not generalize to other types of degradations well. Recently, an approach to first map images downsampled by unknown filters to bicubicly downsampled look-alike images was proposed to successfully super-resolve such images. In this paper, we show that any inverse problem can be formulated by first mapping the input degraded images to an intermediate domain, and then training a second network to form output images from these intermediate images. Furthermore, the best intermediate domain may vary according to the task. Our experimental results demonstrate that this two-stage domain-adapted training strategy does not only achieve better results on a given class of unknown degradations but can also generalize to other unseen classes of degradations better.