![](bg3.png)
Figure 4: Human face image. Enlarged details are for AHD
and in-camera JPEG.
as before used at 24 mm, tripod, 1/200s, f8, man-
ual focus with LiveView) and a human face (Canon
24-105 as before used at 55mm, 1/50s f5.6, auto-
focus). The experimental setup is based on a high
quality 1900x1200 pixel monitor (17” MacBookPro
notebook computer) and the four algorithms (each im-
age being of 960x600 pixels) are presented together
(given a specific photo) in the same image in order to
give to the subject a direct way to compare results. As
in (Longere et al., 2002) the perceptual question was
which was the most pleasant and detailed image. In
this case also the least pleasant and detailed one was
requested. The time left to the subject for the image
was about 30 seconds.
The involved volunteers were 47, with a mean age
of 30 years, mainly males. The original raw and jpg
images have been cropped (without scaling) and ad-
justed in terms of levels, contrast and sharpening as
described in (Longere et al., 2002) in order to put all
algorithms on the same level of sharpness and col-
ors. All original raw images and test images are avail-
able as soon as an internal report more extended with
several more details
1
. Volunteers were also asked
to declare eyesight problems (color issues were not
present). Volunteers involved in eyesight problems
were about half of the total. Finally volunteers were
asked to assess their level in expertise in digital im-
age photography. Each volunteer was involved in only
one session, in which he/she was asked to give a pref-
erence on eight images, that is two slides for each
photo. In the second slide the order of the four al-
gorithms used to process the photo was changed in
order to verify if the volunteer is able to give again
the same preference. The test requested no more than
fifteen minutes for each person. It is important to note
that it was possible also to choose no difference.
4 PERCEPTUAL RESULTS
In this Section the perceptual results will be pre-
sented, in order to show how data have been collected.
1
http://staff.polito.it/bartolomeo.montrucchio/
VISAPP2013/
In Fig.5 are presented the results for ISO 12233 chart
image, in Fig.6 are presented the results for the macro
photo, in Fig.7 are presented the results for the ur-
ban photo, and finally in Fig.8 are presented the re-
sults for the human face photo. People who had eye-
sight problems (corrected) showed a result very sim-
ilar to the people without problems. For this reason
specific results will be omitted here. From the per-
ceptual results just reported, it appears that the best
(with objective metrics) algorithm, AHD, is not so
good from a perceptual point of view. In fact, even
if seeing accurately Fig.1, Fig.2, Fig.3 and Fig.4, it is
possible to say that AHD is normally better than the
other (probably with some doubt in ISO 12233 chart
image), results of the perceptual comparison say that
AHD is for sure better than the other only in the ur-
ban image. In fact in the chart image the best algo-
rithm appears to be JPEG, with a good consistency
(Fig.5) between slides 1 and 2; the reason is proba-
bly that JPEG, being in this case a demosaicing plus
a lossy algorithm, smooths high frequencies, reduc-
ing aliasing. Please note that volunteers have told that
even without colored aliasing they would have cho-
sen again JPEG, generally. In the macro image there
is a great confusion, because AHD wins only in slide
2, there is very few coherency between slide 1 and 2
and the people indicating that there is no differences
among the images are more than 10 (Fig.6). In the
urban image, as told before, AHD wins very clearly.
On 47 people, 40 are able to see the superiority of
AHD. The reason is probably that the aliasing and the
lack of details of the other algorithms make the com-
parison easy (Fig.7). For the human face image the
winner is again AHD (Fig.8), but it is not a clear win-
ner, because only around 50% of the people choose
AHD. The most interesting results are with the peo-
ple that were coherent between slide 1 and slide 2.
This double test, simply mixing the order of the im-
ages, has been able to find true expert people, or at
least people able to find a perceptual meaning in the
images. In macro and human face photos only half or
less of the volunteers were able to find again the best
image, while in the urban image AHD was also easy
to be found and in the ISO chart again volunteers did
not change their opinion (in this case choosing mainly
JPEG).
5 CONCLUSIONS
A perceptual comparison of three demosaicing algo-
rithms and in-camera integrated demosaicing (with
lossy compression) has been performed. The sub-
jective experiments have shown, involving 47 volun-
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