Open-vocabulary object detection upon frozen imaginative and prescient and language fashions – Google AI Weblog


Detection is a elementary imaginative and prescient process that goals to localize and acknowledge objects in a picture. Nevertheless, the info assortment means of manually annotating bounding containers or occasion masks is tedious and expensive, which limits the fashionable detection vocabulary dimension to roughly 1,000 object courses. That is orders of magnitude smaller than the vocabulary folks use to explain the visible world and leaves out many classes. Latest imaginative and prescient and language fashions (VLMs), reminiscent of CLIP, have demonstrated improved open-vocabulary visible recognition capabilities via studying from Web-scale image-text pairs. These VLMs are utilized to zero-shot classification utilizing frozen mannequin weights with out the necessity for fine-tuning, which stands in stark distinction to the prevailing paradigms used for retraining or fine-tuning VLMs for open-vocabulary detection duties.

Intuitively, to align the picture content material with the textual content description throughout coaching, VLMs could be taught region-sensitive and discriminative options which are transferable to object detection. Surprisingly, options of a frozen VLM comprise wealthy data which are each area delicate for describing object shapes (second column under) and discriminative for area classification (third column under). In reality, characteristic grouping can properly delineate object boundaries with none supervision. This motivates us to discover using frozen VLMs for open-vocabulary object detection with the aim to develop detection past the restricted set of annotated classes.

We discover the potential of frozen imaginative and prescient and language options for open-vocabulary detection. The Ok-Means characteristic grouping reveals wealthy semantic and region-sensitive data the place object boundaries are properly delineated (column 2). The identical frozen options can classify groundtruth (GT) areas properly with out fine-tuning (column 3).

In “F-VLM: Open-Vocabulary Object Detection upon Frozen Imaginative and prescient and Language Fashions”, introduced at ICLR 2023, we introduce a easy and scalable open-vocabulary detection method constructed upon frozen VLMs. F-VLM reduces the coaching complexity of an open-vocabulary detector to under that of a normal detector, obviating the necessity for information distillation, detection-tailored pre-training, or weakly supervised studying. We show that by preserving the information of pre-trained VLMs utterly, F-VLM maintains the same philosophy to ViTDet and decouples detector-specific studying from the extra task-agnostic imaginative and prescient information within the detector spine. We’re additionally releasing the F-VLM code together with a demo on our undertaking web page.

Studying upon frozen imaginative and prescient and language fashions

We want to retain the information of pretrained VLMs as a lot as potential with a view to attenuate effort and value wanted to adapt them for open-vocabulary detection. We use a frozen VLM picture encoder because the detector spine and a textual content encoder for caching the detection textual content embeddings of offline dataset vocabulary. We take this VLM spine and fix a detector head, which predicts object areas for localization and outputs detection scores that point out the likelihood of a detected field being of a sure class. The detection scores are the cosine similarity of area options (a set of bounding containers that the detector head outputs) and class textual content embeddings. The class textual content embeddings are obtained by feeding the class names via the textual content mannequin of pretrained VLM (which has each picture and textual content fashions)r.

The VLM picture encoder consists of two components: 1) a characteristic extractor and a couple of) a characteristic pooling layer. We undertake the characteristic extractor for detector head coaching, which is the one step we practice (on customary detection information), to permit us to instantly use frozen weights, inheriting wealthy semantic information (e.g., long-tailed classes like martini, fedora hat, pennant) from the VLM spine. The detection losses embody field regression and classification losses.

At coaching time, F-VLM is solely a detector with the final classification layer changed by base-category textual content embeddings.

Area-level open-vocabulary recognition

The power to carry out open-vocabulary recognition at area stage (i.e., bounding field stage versus picture stage) is integral to F-VLM. Because the spine options are frozen, they don’t overfit to the coaching classes (e.g., donut, zebra) and will be instantly cropped for region-level classification. F-VLM performs this open-vocabulary classification solely at check time. To acquire the VLM options for a area, we apply the characteristic pooling layer on the cropped spine output options. As a result of the pooling layer requires fixed-size inputs, e.g., 7×7 for ResNet50 (R50) CLIP spine, we crop and resize the area options with the ROI-Align layer (proven under). In contrast to present open-vocabulary detection approaches, we don’t crop and resize the RGB picture areas and cache their embeddings in a separate offline course of, however practice the detector head in a single stage. That is easier and makes extra environment friendly use of disk cupboard space.. As well as, we don’t crop VLM area options throughout coaching as a result of the spine options are frozen.

Regardless of by no means being educated on areas, the cropped area options preserve good open-vocabulary recognition functionality. Nevertheless, we observe the cropped area options usually are not delicate sufficient to the localization high quality of the areas, i.e., a loosely vs. tightly localized field each have related options. This can be good for classification, however is problematic for detection as a result of we want the detection scores to replicate localization high quality as properly. To treatment this, we apply the geometric imply to mix the VLM scores with the detection scores for every area and class. The VLM scores point out the likelihood of a detection field being of a sure class based on the pretrained VLM. The detection scores point out the category likelihood distribution of every field primarily based on the similarity of area options and enter textual content embeddings.

At check time, F-VLM makes use of the area proposals to crop out the top-level options of the VLM spine and compute the VLM rating per area. The educated detector head gives the detection containers and masks, whereas the ultimate detection scores are a mixture of detection and VLM scores.


We apply F-VLM to the favored LVIS open-vocabulary detection benchmark. On the system-level, the very best F-VLM achieves 32.8 common precision (AP) on uncommon classes (APr), which outperforms the state-of-the-art by 6.5 masks APr and plenty of different approaches primarily based on information distillation, pre-training, or joint coaching with weak supervision. F-VLM exhibits sturdy scaling property with frozen mannequin capability, whereas the variety of trainable parameters is fastened. Furthermore, F-VLM generalizes and scales properly within the switch detection duties (e.g., Objects365 and Ego4D datasets) by merely changing the vocabularies with out fine-tuning the mannequin. We check the LVIS-trained fashions on the favored Objects365 datasets and show that the mannequin can work very properly with out coaching on in-domain detection information.

F-VLM outperforms the state-of-the-art (SOTA) on LVIS open-vocabulary detection benchmark and switch object detection. On the x-axis, we present the LVIS metric masks AP on uncommon classes (APr), and the Objects365 (O365) metric field AP on all classes. The sizes of the detector backbones are as follows: Small(R50), Base (R50x4), Massive(R50x16), Large(R50x64). The naming follows CLIP conference.

We visualize F-VLM on open-vocabulary detection and switch detection duties (proven under). On LVIS and Objects365, F-VLM accurately detects each novel and customary objects. A key good thing about open-vocabulary detection is to check on out-of-distribution information with classes given by customers on the fly. See the F-VLM paper for extra visualization on LVIS, Objects365 and Ego4D datasets.

F-VLM open-vocabulary and switch detections. High: Open-vocabulary detection on LVIS. We solely present the novel classes for readability. Backside: Switch to Objects365 dataset exhibits correct detection of many classes. Novel classes detected: fedora, martini, pennant, soccer helmet (LVIS); slide (Objects365).

Coaching effectivity

We present that F-VLM can obtain high efficiency with a lot much less computational assets within the desk under. In comparison with the state-of-the-art method, F-VLM can obtain higher efficiency with 226x fewer assets and 57x sooner wall clock time. Aside from coaching useful resource financial savings, F-VLM has potential for substantial reminiscence financial savings at coaching time by working the spine in inference mode. The F-VLM system runs virtually as quick as a normal detector at inference time, as a result of the one addition is a single consideration pooling layer on the detected area options.

Methodology       APr       Coaching Epochs       Coaching Value
      Coaching Value Financial savings      
SOTA       26.3       460       8,000       1x      
F-VLM       32.8       118       565       14x      
F-VLM       31.0       14.7       71       113x      
F-VLM       27.7       7.4       35       226x      

We offer extra outcomes utilizing the shorter Detectron2 coaching recipes (12 and 36 epochs), and present equally sturdy efficiency by utilizing a frozen spine. The default setting is marked in grey.

Spine       Massive Scale Jitter       #Epochs       Batch Dimension       APr      
R50             12       16       18.1      
R50             36       64       18.5      
R50             100       256       18.6      
R50x64             12       16       31.9      
R50x64             36       64       32.6      
R50x64             100       256       32.8      


We current F-VLM – a easy open-vocabulary detection technique which harnesses the ability of frozen pre-trained giant vision-language fashions to supply detection of novel objects. That is performed and not using a want for information distillation, detection-tailored pre-training, or weakly supervised studying. Our method affords vital compute financial savings and obviates the necessity for image-level labels. F-VLM achieves the brand new state-of-the-art in open-vocabulary detection on the LVIS benchmark at system stage, and exhibits very aggressive switch detection on different datasets. We hope this research can each facilitate additional analysis in novel-object detection and assist the group discover frozen VLMs for a wider vary of imaginative and prescient duties.


This work is carried out by Weicheng Kuo, Yin Cui, Xiuye Gu, AJ Piergiovanni, and Anelia Angelova. We wish to thank our colleagues at Google Analysis for his or her recommendation and useful discussions.


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