The Venus Transit 2004
... Photos (541-550)
On this and the other pages in the VT-2004 Photo Archive , photos are displayed which are related to Venus, the Sun and/or the Venus Transit. They were obtained in many different places. Some of these photos were elected "VT 2004 Photo of the Day" .
All photos on this page may be downloaded and used, provided the photographers (authors) and the VT-2004 programme are indicated as source.
Processed Images Illustrating Black Drop Phenomenon
The images on this page serve to illustrate the "Black Drop" effect. The images were obtained at the Ondrejov observatory (Czech Republic) in white light (images 1 - 4; South is towards the top) and through an H-alpha filter (images 5 - 8; South is down).
The image processing was performed by Stanislava Simberova , by means of the procedures available to everybody via the VT-2004 Image Processing Pages
Black Drop Phenomenon (1)
[603 x 451 - 89k]
Black Drop Phenomenon (2)
[603 x 451 - 88k]
Black Drop Phenomenon (3)
[603 x 451 - 85k]
Black Drop Phenomenon (4)
[603 x 451 - 112k]
Photos 1 - 4 show the effect at the moment of the second contact and the development in time. In each of these photos, the lower image (in B/W) is the observed, original (raw) one. In the upper part, there are four processed images (A, B, C and D from left to right), based on the original one. They were prepared by using different processing techniques.
Images A and B: Edge crispening . They were made by discrete convolution with high-pass form of the impulse response H(A), H(B).
Image C: Edge detection . Edges characterize object boundaries and are therefore useful for segmentation, registration, and identification of objects within scenes. Typically, edge, line and spot locations are specified by darker pixels against a lighter background. This is exactly the case during the Venus transit across over the bright surface on the Sun. These techniques are based on the first-order derivative and involve the generation of gradients in two orthogonal directions in an image. The row and column gradients involve a linear combination of pixels within a small neighborhood. For these images, a Sobel filter was applied.
D: Edge detection. This method is based on the second derivative. An edge is marked if a significant spatial change occurs in the second derivative. It was performed by a Laplace filter.
The fourth image has an insert in which the image was transformed by discrete high-pass convolution and displayed using the isophot transformation table. The colours in the image corresponds to the exact density ranges.
Black Drop Phenomenon (5)
[603 x 451 - 184k]
Black Drop Phenomenon (6)
[603 x 451 - 192k]
Photos 5 and 6 display H_alpha (wavelength 656.3 nm) images of the solar chromosphere, obtained just before the 1st contact. Photo 5 is a reproduction of the original image, with the different features designated. Photo 6 is the same image, but now with an insert image that has been processed: noise cleaning by means of a special smoothing filter and non-linear contrast manipulation function application.
Black Drop Phenomenon (7)
[603 x 451 - 192k]
Black Drop Phenomenon (8)
[452 x 452 - 88k]
Photo 7 shows the situation just before the 2nd contact; on the original image, the photosphere "border" is indicated with a traced line. Photo 8 is an enlargement from Photo 7, with the point of the 2nd contact at the level of the photosphere marked.