DTO-700-17A

Comparative Study of

HDTV and NTSC Imagery

 

 

September 22, 1999

 

 

 

The Image Science and Analysis Group

Space Science Branch /SN3

NASA — Johnson Space Center

 


 

DTO-700-17A

Comparative Study of

HDTV and NTSC Imagery

 

During STS-93 a set of similar scenes were recorded on-orbit with both a handheld HDTV camera and a payload bay NTSC camera. This report is an assessment of the imagery improvement provided by HDTV when compared to similar NTSC views. The difference is dramatic and clearly visible in side by side comparisons.

Image Acquisition

An HDCAM VTR and HDTV monitor were set up in the VDAS lab for three days. During this time HDTV scenes were screened and selected along with planned NTSC companion views taken from a payload bay camera. Launch, landing, and post landing walk-around HDTV views were also selected for comparison to similar unplanned NTSC scenes recorded during these events. NTSC views were digitized from a D2 tape provided by Johnson TV. Downconverted HDTV scenes were digitized in the VDAS from the HDCAM VTR in letterbox and cropped formats. Native high resolution HDTV image frames were supplied by NASDA.

Image Analysis

Analysis by the SN3/Image Science and Analysis Group shows that the STS-93 HDTV video is dramatically clearer, sharper and brighter than the corresponding NTSC video. The amount of detail acquired with HDTV is remarkable. Below are observations about the selected views.

With on-orbit HDTV acquired during good lighting, small features in the Shuttle payload bay are distinct and measurable, and edges are sharp and clear. In the corresponding NTSC video, the same small objects are blurry or not resolvable, and the edges are soft and fuzzy. In other words, the NTSC scenes appear out of focus in comparison with HDTV. Rivet holes, individual tile edges, handrail surfaces, floating debris, and MLI fabric wrinkles are examples of objects in the payload bay that are easily resolvable in the HDTV scenes, but not in the corresponding NTSC video. In low light on-orbit scenes, there is considerable noise apparent in the NTSC images. The corresponding HDTV images appear relatively free of noise. Color maintains its stability in dark scenes with HDTV, while blotches of green, blue, and red are evident in the NTSC views. Therefore on-orbit anomaly detection and anomaly image analysis would be improved with HDTV.

In examining views of the landing sequence, detailed structure, such as landing strut assemblies and inboard/outboard tires, were clearly visible in the HDTV images that were not seen as clearly in the corresponding NTSC images. With the HDTV, critical events such as wheel touchdown and pilot and dragchute deployment/release are sharp and clearly seen, even in the nighttime conditions. Therefore our standard analyses of Shuttle sink rate and landing event timing would be improved with HDTV.

Another convincing comparison, seen during the post-landing orbiter walk-around, was of the inside of SSME#3 where the source of the hot-wall propellant leak occurred. In the NTSC video, a vague area of discoloration could be seen but no clear details. In the HDTV video however, the three punctures in the coolant tubes can clearly be made out in spite of the poor lighting.

In summary, from this assessment, engineering image analysis for mission support would be greatly improved with the higher quality HDTV imagery. Examples of improved image analysis support include anomaly detection and analysis, landing sink rate analysis, and critical launch and landing event timing.

Image Comparisons

Each comparison case consists of three image instances; an HDTV image (1920 x1080 pixels), a Downconverted HDTV image (646 x 486 pixels) and an NTSC image (646 x 486 pixels). The entire frame of each of these three instances has been included on a hardcopy print so that they can be compared visually. Two square regions of interest have been extracted from each image and enlarged. Each of these enlarged areas represents a corresponding region of interest in all of the three of the images so that they can be compared.


Figure A - Comparison of images with a similar vertical field of view

Figure A (low resolution, 288K)

Figure A (high resolution, 3.4MB)

Figure B - Comparison of images with a similar horizontal field of view

Figure B (low resolution, 288K)

Figure B (high resolution, 3.3MB)

Figure C - Comparison of low light views

Figure C (low resolution, 256K)

Figure C (high resolution, 3.3MB)

Figure D - Comparison of STS-93 SSME#3 engine hot-wall leak views

Figure D (low resolution, 416K)

Figure D (high resolution, 6MB)

Figure E - Comparison of STS-93 landing views

Figure E (low resolution, 416K)

Figure E (high resolution, 4.3MB)

Figure F - Comparison of landing gear views

Figure F (low resolution, 832K)

Figure F (high resolution, 3MB)


Conclusion

Video quality is the primary factor in achieving accurate image analysis. HDTV provides a remarkable advancement in video quality. These advancements will enable IS&AG to tackle image analysis tasks that were previously not feasible because of the lack of image quality. The image detail inherent to HDTV will also make all image analysis tasks much more accurate for mission contingencies.