Schomaker, de Leau & Vuurpijl

(multiple outlines per photograph are allowed)

animal collection outlines

 




typical bodyworks shape of motor bicycle

(note the distribution of points of high curvature along the outline)

A query to find an engine

Schomaker, de Leau & Vuurpijl

 




bodyworks shapes of motor bicycle

Schomaker, de Leau & Vuurpijl

 




motor-bicycle collection driver shapes

Schomaker, de Leau & Vuurpijl

 




motor-bicycle collection engine shapes

Schomaker, de Leau & Vuurpijl

 




motor-bicycle collection frame shapes

Schomaker, de Leau & Vuurpijl

 




algorithm matching possibilities

• (a) match the query outline ([(x)\vec],[(y)\vec]) with all outlines which are present in the database
  
  
• (b) match the image I(x,y) content within the outline ([(x)\vec],[(y)\vec]) with existing templates in the database,
  
  
• (c) match a query outline with image edges DI(x,y) of unseen photographs (!)

Simple 1-NN matching will be used for all feature categories.

Schomaker, de Leau & Vuurpijl

 




algorithm outline features

The raw outline is resampled to a fixed number of samples (100). The center of gravity is translated to (0,0), the size is normalized to an rms radius (s_r) of one, yielding the normalized outline ([^[x\vec]],[^[y\vec]]). From the starting point B, the matching process will try both clockwise and counter-clockwise directions, retaining the best result of both match variants. Other normalizations such as left/right or up/down mirroring are optional. In addition, the running angles (cos(f),sin(f)) are added as feature group, as well as the histogram p(f).

Schomaker, de Leau & Vuurpijl

 




algorithm image features

The following 68 features were derived from the pixels within the closed object outline:

color centroids The center of gravity for each of the RGB-channels. This gives 6 features: R(x,y), G(x,y) and B(x,y)

color histogram The histogram of the occurrence of 8 main colors: black, blue, green, cyan, red, magenta, yellow and white

intensity histogram A histogram for 10 levels of pixel intensity

RGB statistics The minimum and maximum values of each of the RGB-channels, and their average and standard-deviation (12 features)

texture descriptors A table of five textures was used, with five statistical features each (25 features)

invariant moments Seven statistical high-order moments[] which are invariant to size and rotation

Schomaker, de Leau & Vuurpijl

 




results
data set

Data set: 200 mixed JPEG and GIF photographs of motor bicycles. Within this set, 750 outlines were drawn around image parts in the following classes: exhaust, wheels, engine, frame, pedal, fuel tank, saddle, driver, mirror, license plate, bodyworks, head light, fuel tank lid, light, rear light, totalling 15 object classes with 50 different outline samples of each object

Schomaker, de Leau & Vuurpijl

 




results
outline matching & within-outline image matching

Results are represented as the average percentage of correct hits in the top-10 hit list (P₁₀), averaged over n = 50 outline instances per class, of which each was used as a probe in nearest-neighbour matching. The query itself was excluded from the matching process.

Query	I. P10 (%)	II. P10 (%)	III. P10 (%)	IV. P10 (%)
	([^x],[^y])	(cosf,sinf)	p(f)	image-based
wheels	77.6	81.8	36.0	58.2
exhaust	75.4	79.4	34.0	34.6
engine	57.0	51.4	31.6	49.6
frame	52.0	33.8	38.8	69.4
pedal	47.4	47.2	22.8	33.0
driver	43.6	43.4	20.2	50.2
saddle	41.4	39.2	15.0	20.2
fuel tank	41.4	43.2	23.2	22.8
mirror	40.6	39.8	11.2	22.4
license plate	36.0	47.8	30.2	21.8
bodywork	31.0	26.6	14.4	22.4
head light	30.6	38.2	13.2	30.4
fuel tank lid	29.6	35.8	25.8	23.4
light	21.6	19.4	11.0	27.4
rear light	14.8	14.8	9.0	33.0

Schomaker, de Leau & Vuurpijl

Whereas in general, the outlines outperform pixel-based features in this experiment, a class-dependent feature selection may yield reversed results.

 




algorithm outline vs edge matching

Ultimately, one will want to use the set of outlines to perform object classification in unseen images, for which only the 'bottom-up' edge representation can be computed. Assuming that scale and translation are already approximately correct, how well can we match the human-generated outlines with the edges?

For each point i on a raw outline (X_i,Y_i), a convolution is calculated as follows. Let DI(x,y) be an estimate of the absolute and smoothed derivative of the luminance gradient of an image I(x,y), averaged over a number of suitable directions. Then the local match between an outline point (X,Y) and the edge representation of the image can be calculated as:

MXiYi,DI = w Sum dx = -w    w Sum dy = -w  DI(Xi+dx,Yi+dy) Sqrt( dx2 +dy2)

(1)

Schomaker, de Leau & Vuurpijl

 




results
outline vs edge matching

Figure 1: Results for the matching process between human-drawn outlines and bottom-up calculated image edges as a percentage of outline instances which are correctly associated with their original image. The two curves represent the results of sorting the hit list on mean convolution output M (solid line) or on the maximum value of M (stippled). This performance measure differs from Table  because here instances are matched as opposed to classes.

Schomaker, de Leau & Vuurpijl

 

Improved outline vs edge matching

The matching results based on outline vs edge matching presented above can be improved. Assuming that an class is often presented in a stereotypical background (cow on a meadow, engine part in shaded metallic textures), it may be useful to perform class-dependent edge matching. This can be done using the human-produced outlines as the target for an MLP edge detector:

Schomaker, Vuurpijl & de Leau

generic edge detector (spurious edge pixels!)

class-dependent edge detector (MLP 49x25x9x1)

(training set: heterogenous set of 100+ motor bicycles, outline$ parts determine the edge target output per 7x7 field)

Note that these results are only preliminary because scale and translation invariance has not been achieved at all here.

Conclusion

• promising results (esp. when compared to HWR problems)
  
  
• succesfully applied to a set of aircraft images
  
  
• computation time...
  
  
• refinement of edge preprocessing will improve the 'bottom-up' search for outlines in unseen images
  
  
• domain-dependent and object-dependent use of features: ideal environment for the multiple-agent paradigm
  
  
• ongoing work: S/N ratios for mouse & pen-based outlines

Schomaker, de Leau & Vuurpijl

List of References

---

File translated from T_EX by T_TH, version 2.51.
On 1 Dec 1999, 12:32.