NASA Releases New Photos of Saturn's Rings and Clouds

skade88 writes "Launched in 1997, Cassini has taken over 300,000 pictures of Saturn since it started orbiting the planet and the mission is due to run through 2017. NASA has released some new photos including: Saturn's rings, clouds, Saturn's moon Janus, and the shadow of another one of Saturn's moons Mimas."

Comments

Black-and-white?

[ClickOnThis]

What's with the black-and-white photos? Didn't Cassini have colour cameras?

Re:Black-and-white?

[wonkey_monkey]

It does, but they cost more to develop. Times are tight.

Re:Black-and-white?

[Anonymous Coward]

From NASA's FAQ page:

Why are so few of the Cassini pictures in color?

Creating color images is a complex task requiring much more labor and computer time than black and white images. This is because all Cassini images are recorded in black and white. The camera records the amount of light (not the color of the light) coming through a filter in front of the sensor. It is the filters that come in color.

To create color images scientists take three black and white images of the same target with the red, green, and blue (RGB) filters. In other words, one image records the amount of red light (using a red filter), another records the amount of green and one the amount of blue light (using green and blue filters respectively). Color renditions of the scene are then constructed on the ground by combining images taken with the different filters.
Unfortunately, these three images are not taken simultaneously. Consequently, intricate fitting and geometric transformations are needed to construct the color image because the spacecraft, planet, rings and moons have all moved a little during the time it takes to record the images using the different filters.

What controls when a picture is taken?

The scientists determine this when they do the observation designs. The path of Cassini is known, as are the paths of the Saturn's moons, so it's a matter of looking at the varying geometry with time and selecting the camera pointing directions and shuttering times that will gather the most scientifically interesting images. These commands are then built into sequences that are sent to the spacecraft from days to weeks in advance of the observations.

Re:Black-and-white?

[JWW]

Also, most color photos from NASA are gong to be in fake color and exaggerated contrast, made to highlight certain features (or impress congressmen), not to look accurate.

Actually, they don't really have a real color view they can show us. Sensors on spacecraft see multi-band (read color) images as single bands representing intensity for each band. These black and white views are actually the view of a particular band filtered on the wavelength of the light it is looking for.

The false-color images derived by NASA generally use 3 bands to create a RGB style image with a single particular band standing in for Red, Green, and Blue. The reason these images are false-color is that often the Red band is all or in part filtering to find infrared light, and the blue is sometimes filtered more toward violet and UV.

They really often times can't make a true color image. Because there is more science value derived from being able to see values in bands that are tuned slightly away from the visible (especially wrt infrared).

Re:Black-and-white?

[PhunkySchtuff]

Because it all comes down to the resolution of the picture. They want as accurate ans as detailed a picture as they can get, and using a mosaic filter over the sensor firstly fixes you to a single set of colour filters, as it has to be precisely aligned with the image sensor elements, and you have to then interpolate image data (ie, guess at filling in missing colour information)

With a b&w sensor, you have more freedom in swapping out filters over the sensor and you aren't interpolating picture information.

Re:Black-and-white?

[meetpi]

Not a dumb question at all, it's actually a very good question. The short answer is that an image taken by a standard digital camera would probably be pretty disappointing.

The first thing to realise is that your eyes aren't really like cameras at all. There's a complex series of interactions in your eyes and brain that take place before you perceive an image. When you take a colour image with a digital camera most people reasonably expect it to match what they see. So, your digital camera manipulates the raw data it gets from its sensors to munge it into a form that looks like what you see. Like the Cassini cameras, a digital camera detects the level of light hitting its sensor and uses different coloured (red, green and blue) filters to turn this back into a colour image. It also often applies various algorithms to the image data to adjust the relative intensities of the light.

The result is an image that's more of less what you see. But there's lots of ways this can fail. Sunsets, for example, are difficult to capture in a way that meets our expectations. If you have an image with a bright area (the sky, say) and a darker area (an area in shadow) it's impossible to get the entire image properly exposed.

When you send a probe a long way from the sun and take photos with a very sensitive camera you get a set of data which you can assemble in lots of different ways, all of which are true representations of the light "seen" by the probe. If NASA attached a typical colour digital camera to the probe they'd just be attaching a much more basic version of the imaging sensors they already have.

So why don't they just process all the RAW images into colour ones? Well, most are pretty dull, and it's not worth the effort. So instead, they make all the raw images available (see them here), which look like a series of black and white images (you can sometimes assemble these into colour images in Photoshop/GIMP). Out of the thousands of images they take only some of them are considered interesting enough to spend some time processing into full colour images.

Re:Black-and-white?

[BeanThere]

You can usually still find the original pictures, but not always easily.

Here is a link to one of those original pictures:

http://www.log24.com/log/pix09A/091127-BlackSquare256-revA.jpg

(What, your eyes can't see electromagnetic radiation outside the visible light range?)

(You actually have it completely the wrong way round; it isn't that 'false' color is 'added' - it's that in reality, there are trillions more 'colors' than our very limited human eyes can see.)

Go to the source...

[SgtXaos]

http://saturn.jpl.nasa.gov/

Has all the images, none of the space.com ads

Re:space.com

[ColdWetDog]

Is there any way to browse the photos elsewhere / without the terrible space.com bloat?

Ah, the plight of the poor, confused AC. Lurk more, post less. Look up just a bit. And come on submitters and "editors" - just link to the primary sites when available not the commercial crapfest.