Ameesh Makadia
I am currently a Research Scientist with Google in NYC.
My research interests lie at the intersection of Computer Vision and Machine Learning.
For more details and a complete publication list please visit my personal site.
Research Areas
Authored Publications
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Learning to Transform for Generalizable Instance-wise Invariance
Utkarsh Singhal
Stella Yu
International Conference on Compute Vision (2023)
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Computer vision research has long aimed to build systems that are robust to spatial transformations found in natural data. Traditionally, this is done using data augmentation
or hard-coding invariances into the architecture. However, too much or too little invariance can hurt, and the correct amount is unknown a priori and dependent on the instance. Ideally, the appropriate invariance would be learned from data and inferred at test-time.
We treat invariance as a prediction problem. Given any image, we use a normalizing flow to predict a distribution over transformations and average the predictions over them. Since this distribution only depends on the instance, we can align instances before classifying them and generalize invariance across classes. The same distribution can also be used to adapt to out-of-distribution poses. This normalizing flow is trained end-to-end and can learn a much larger range of transformations than Augerino and InstaAug. When used as data augmentation, our method shows accuracy and robustness gains on CIFAR 10, CIFAR10-LT, and TinyImageNet.
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Scaling Spherical CNNs
Jean-Jacques Slotine
International Conference on Machine Learning (ICML) (2023)
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Spherical CNNs generalize CNNs to functions on the sphere, by using spherical convolutions as the main linear operation. The most accurate and efficient way to compute spherical convolutions is in the spectral domain (via the convolution theorem), but this is still much more costly than the usual planar convolutions. For this reason, applications of spherical CNNs have so far been limited to small problems that can be approached with low model capacity. In this work, we show how spherical CNNs can be scaled for much larger problems. To achieve this, we made critical improvements including an implementation of core operations to exploit hardware accelerator characteristics, introducing novel variants of common model components, and showing how to construct application-specific input representations that exploit the properties of our model. Experiments show our larger spherical CNNs reach state-of-the-art on several targets of the QM9 molecular benchmark, which was previously dominated by equivariant graph neural networks, and achieve competitive performance on multiple weather forecasting tasks.
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ASIC: Aligning Sparse in-the-wild Image Collections
Kamal Gupta
Varun Jampani
Abhinav Shrivastava
Abhishek Kar
International Conference on Computer Vision (ICCV) (2023)
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We present a method for joint alignment of sparse in-thewild image collections of an object category. Most prior works assume either ground-truth keypoint annotations or a large dataset of images of a single object category. However, neither of the above assumptions hold true for the longtail of the objects present in the world. We present a selfsupervised technique that directly optimizes on a sparse collection of images of a particular object/object category to obtain consistent dense correspondences across the collection. We use pairwise nearest neighbors obtained from deep features of a pre-trained vision transformer (ViT) model as noisy and sparse keypoint matches and make them dense and accurate matches by optimizing a neural network that jointly maps the image collection into a learned canonical grid. Experiments on CUB and SPair-71k benchmarks demonstrate that our method can produce globally consistent and higher quality correspondences across the image collection when compared to existing self-supervised methods. Code and other material will be made available at https://kampta.github.io/asic.
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LU-NeRF: Scene and Pose Estimation by Synchronizing Local Unposed NeRFs
Zezhou Cheng
Varun Jampani
Abhishek Kar
Subhransu Maji
International Conference on Computer Vision (ICCV) (2023)
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A critical obstacle preventing NeRF models from being deployed broadly in the wild is their reliance on accurate camera poses. Consequently, there is growing interest in extending NeRF models to jointly optimize camera poses and scene representation, which offers an alternative to offthe-shelf SfM pipelines which have well-understood failure modes. Existing approaches for unposed NeRF operate under limiting assumptions, such as a prior pose distribution or coarse pose initialization, making them less effective in a general setting. In this work, we propose a novel approach, LU-NeRF, that jointly estimates camera poses and neural radiance fields with relaxed assumptions on pose configuration. Our approach operates in a local-to-global manner, where we first optimize over local subsets of the data, dubbed “mini-scenes.” LU-NeRF estimates local pose and geometry for this challenging few-shot task. The mini-scene
poses are brought into a global reference frame through a robust pose synchronization step, where a final global optimization of pose and scene can be performed. We show our LU-NeRF pipeline outperforms prior attempts at unposed NeRF without making restrictive assumptions on the pose prior. This allows us to operate in the general SE(3) pose setting, unlike the baselines. Our results also indicate our model can be complementary to feature-based SfM
pipelines as it compares favorably to COLMAP on lowtexture and low-resolution images.
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NAVI: Category-Agnostic Image Collections with High-Quality 3D Shape and Pose Annotations
Varun Jampani
Andreas Engelhardt
Arjun Karpur
Karen Truong
Kyle Sargent
Ricardo Martin-Brualla
Kaushal Patel
Daniel Vlasic
Vittorio Ferrari
Ce Liu
Neural Information Processing Systems (NeurIPS) (2023)
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Recent advances in neural reconstruction enable high-quality 3D object reconstruction from casually captured image collections. Current techniques mostly analyze their progress on relatively simple image collections where SfM techniques can provide ground-truth (GT) camera poses. We note that SfM techniques tend to fail on in-the-wild image collections such as image search results with varying backgrounds and illuminations. To enable systematic research progress on 3D reconstruction from casual image captures, we propose a new dataset of image collections called `NAVI' consisting of category-agnostic image collections of objects with high-quality 3D scans along with per-image 2D-3D alignments providing near-perfect GT camera parameters. These 2D-3D alignments allows to extract derivative annotations such as dense pixel correspondences, depth and segmentation maps. We demonstrate the use of NAVI image collections on different problem settings and show that NAVI enables more thorough evaluations that were not possible with existing datasets. We believe NAVI is beneficial for systematic research progress on 3D reconstruction and correspondence estimation. Project page: \url{https://navidataset.github.io}
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Learning ABCs: Approximate Bijective Correspondence for isolating factors of variation with weak supervision
Kieran Alexander Murphy
Varun Jampani
Computer vision and pattern recognition (CVPR) 2022 (to appear)
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Representational learning forms the backbone of most deep learning applications, and the value of a learned representation depends on its information content about the different factors of variation.
Learning good representations is intimately tied to the nature of supervision and the learning algorithm.
We propose a novel algorithm that relies on a weak form of supervision where the data is partitioned into sets according to certain \textit{inactive} factors of variation.
Our key insight is that by seeking approximate correspondence between elements of different sets, we learn strong representations that exclude the inactive factors of variation and isolate the \textit{active} factors which vary within all sets.
We demonstrate that the method can work in a semi-supervised scenario, and that a portion of the unsupervised data can belong to a different domain entirely, as long as the same active factors of variation are present.
By folding in data augmentation to suppress additional nuisance factors, we are able to further control the content of the learned representations.
We outperform competing baselines on the challenging problem of synthetic-to-real object pose transfer.
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Light Field Neural Rendering
Leonid Sigal
Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR) (2022)
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Classical light field rendering for novel view synthesis can
accurately reproduce view-dependent effects such as reflection,
refraction, and translucency, but requires a dense view sampling of
the scene. Methods based on geometric reconstruction need only sparse
views, but cannot accurately model non-Lambertian effects. We
introduce a model that combines the strengths and mitigates the
limitations of these two directions. By operating on a
four-dimensional representation of the light field, our model learns
to represent view-dependent effects accurately. By enforcing geometric
constraints during training and inference, the scene geometry is
implicitly learned from a sparse set of views. Concretely, we
introduce a two-stage transformer-based model that first aggregates
features along epipolar lines, then aggregates features along
reference views to produce the color of a target ray. Our model
outperforms the state-of-the-art on multiple forward-facing and 360◦
datasets, with larger margins on scenes with severe view-dependent
variations. Code and results can be found at light-field-neural-
rendering.github.io.
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Generalizable Patch-Based Neural Rendering
Leonid Sigal
European Conference on Computer Vision (2022) (to appear)
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Neural rendering has received tremendous attention since the advent of
Neural Radiance Fields (NeRF), and has pushed the state-of-the-art on
novel-view synthesis considerably. The recent focus has been on models
that overfit to a single scene, and the few attempts to learn models
that can synthesize novel views of unseen scenes mostly consist of
combining deep convolutional features with a NeRF-like model. We
propose a different paradigm, where no deep visual features and no
NeRF-like volume rendering are needed. Our method is capable of
predicting the color of a target ray in a novel scene directly, just
from a collection of patches sampled from the scene. We first leverage
epipolar geometry to extract patches along the epipolar lines of each
reference view. Each patch is linearly projected into a 1D feature
vector and a sequence of transformers process the collection. For
positional encoding, we parameterize rays as in a light field
representation, with the crucial difference that the coordinates are
canonicalized with respect to the target ray, which makes our method
independent of the reference frame and improves generalization. We
show that our approach outperforms the state-of-the-art on novel view
synthesis of unseen scenes even when being trained with considerably
less data than prior work. Our code is available at
https://mohammedsuhail.net/gen_patch_neural_rendering.
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De-rendering the World’s Revolutionary Artefacts
Elliott Wu
Jiajun Wu
Angjoo Kanazawa
Computer Vision and Pattern Recognition (CVPR) (2021)
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Recent works have shown exciting results in unsupervised image de-rendering—learning to decompose 3D shape, appearance, and lighting from single-image collections without explicit supervision. However, many of these assume simplistic material and lighting models. We propose a method, termed RADAR (Revolutionary Artefact De-rendering And Re-rendering), that can recover environment illumination and surface materials from real single-image collections, relying neither on explicit 3D supervision, nor on multi-view or multi-light images. Specifically, we focus on rotationally symmetric artefacts that exhibit challenging surface properties including specular reflections, such as vases. We introduce a novel self-supervised albedo discriminator, which allows the model to recover plausible albedo without requiring any ground-truth during training. In conjunction with a shape reconstruction module exploiting rotational symmetry, we present an end-to-end learning framework that is able to de-render the world's revolutionary artefacts. We conduct experiments on a real vase dataset and demonstrate compelling decomposition results, allowing for applications including free-viewpoint rendering and relighting.
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Infinite Nature: Perpetual View Synthesis of Natural Scenes from a Single Image
Varun Jampani
Angjoo Kanazawa
International Conference on Computer Vision (ICCV) (2021)
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We introduce the problem of perpetual view generation—long-range generation of novel views corresponding to an arbitrarily long camera trajectory given a single image. This is a challenging problem that goes far beyond the capabilities of current view synthesis methods, which work for a limited range of viewpoints and quickly degenerate when presented with a large camera motion. Methods designed for video generation also have limited ability to produce long video sequences and are often agnostic to scene geometry. We take a hybrid approach that integrates both geometry and image synthesis in an iterative render, refine, and repeat framework, allowing for long-range generation that cover large distances after hundreds of frames. Our approach can be trained from a set of monocular video sequences without any manual annotation. We propose a dataset of aerial footage of natural coastal scenes, and compare our method with recent view synthesis and conditional video generation baselines, showing that it can generate plausible scenes for much longer time horizons over large camera trajectories compared to existing methods.
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