
Multi-Scale Structural-aware Exposure Correction
for Endoscopic Imaging
Axel Garc´
ıa-Vega1, Ricardo Espinosa2,4, Luis Ram´
ırez-Guzm´
an1, Thomas Bazin3, Luis Falc´
on-Morales1,
Gilberto Ochoa-Ruiz1, Dominique Lamarque3and Christian Daul2,
Abstract—Endoscopy is the most widely used imaging tech-
nique for the diagnosis of cancerous lesions in hollow organs.
However, endoscopic images are often affected by illumination
artefacts: image parts may be over- or underexposed according
to the light source pose and the tissue orientation. These artifacts
have a strong negative impact on the performance of computer
vision or AI-based diagnosis tools. Although endoscopic image
enhancement methods are greatly required, little effort has been
devoted to over- and under-exposition enhancement in real-time.
This contribution presents an extension to the objective function
of LMSPEC, a method originally introduced to enhance images
from natural scenes. It is used here for the exposure correction in
endoscopic imaging and the preservation of structural informa-
tion. To the best of our knowledge, this contribution is the first
one that addresses the enhancement of endoscopic images using
deep learning (DL) methods. Tested on the Endo4IE dataset, the
proposed implementation has yielded a significant improvement
over LMSPEC reaching a SSIM increase of 4.40% and 4.21%
for over- and underexposed images, respectively.
Index Terms—image enhancement, endoscopy, exposure cor-
rection, Computer-Aided Diagnosis
I. INTRODUCTION
Endoscopy plays a central role in minimally invasive
surgery or for carrying out examinations in hollow organs,
such as the colon or the stomach. In recent years, computer
aided endoscopy has become an important area of research.
In particular, Computer Vision (CV) has the potential of
becoming an essential tool for assisting endoscopists in various
tasks [7], [14], [20].
However, a major hurdle that most of these CV methods
must face is related to the uncontrolled and highly changing
illumination conditions in endoscopic scenes. Figure 1 shows
two colonoscopic images in which strong illumination changes
are visible. Such uncontrolled lighting affects the robustness
of Computer-Aided Detection (CADe) and Diagnosis (CADx).
The performance of techniques for recovering extended sur-
faces of hollow organs (such as SLAM [8] or Structure for
Motion [15]) is also affected by uncontrolled lighting. These
strong photo-metric variations are due to non-optimal light
source poses, moist surfaces, and occlusions that lead to under-
or overexposed video-frames parts [13].
Identify applicable funding agency here. If none, delete this.
1School of Engineering and Sciences, Tecnologico de Monterrey, Mexico
2CRAN (UMR 7039, Universit´
e de Lorraine and CNRS), Nancy, France
3Hˆ
opital Ambroise Par´
e (AP-HP), Boulogne-Billancourt France
4Universidad Panamericana, Aguascalientes, Mexico
*Contacts: gilberto.ochoa@tec.mx, christian.daul@univ-lorraine.fr
Fig. 1: Strong illumination change example in almost con-
secutive frames of a colonoscopic image sequence. (a) This
image was acquired in appropriate lighting conditions. (b) Few
frames later, the image is overexposed in its lower left region
and underexposed in the remaining frame part.
Therefore, any improvements of endoscopic image content
quality could considerably boost the efficiency of CV- and AI-
based CAD tools. In this regard, various challenges have been
proposed in conferences to foster the development of algo-
rithms which can be bench-marked in terms of generalization
capabilities. One such challenge is the Endoscopic Artifact
Detection challenge (EAD, [3]), with includes various types of
endoscopic artefacts for developing novel image preprocessing
algorithms.
The results obtained by numerous methods in the EAD
challenge have shown that image enhancement (IE) algo-
rithms are of high interest for improving the robustness and
generalization capabilities of endoscopic image preprocessing
techniques. This contribution focuses on the exposure correc-
tion in white light endoscopy. It is noticeable that this issue
has only been partially addressed in the IE field, as most
methods (see [1]) were dedicated to the correction of either
under- or over-exposed images, but did not deal with both
effects occurring concurrently. Contrary to images of natural
scenes, in endoscopy imaging it is common that both types of
non-optimal exposures simultaneously affect frames. Thus, a
preprocessing algorithm should be able to detect and correct
in real-time all types of inappropriate exposures.
Garc´
ıa-Vega et al. proposed a paired “normal-exposed” im-
age dataset [9], [10] to assess the ability of machine learning-
based methods to correct the effects of non-optimal lighting
conditions. However, the need for both accurate and real-
time IE techniques highlighted the shortcomings of most cur-
arXiv:2210.15033v1 [eess.IV] 26 Oct 2022