Frequently Asked Questions About Astronaut-Acquired Photographs

Questions about access to photographs:

How do I know if an image on the website is the best possible quality?
How are digital camera images compressed and brought down from orbit?
What kind of color correction is used on images taken with a digital camera?
Can I get a copy of an image at 300 dpi?

How do I know if an image on the website is the best possible quality?

Digital images posted to our website come from a variety of sources--some have been scanned from film and some were acquired digitally. The information in the "CAMERA" field tells you what kind of camera, and the image in the "FILM" field tells you what kind of film or what kind of CCD for a digital camera. Images scanned from film will vary in quality because they may have been scanned in the past using video technology, scanned by hand, or scanned in a batch mode where setting were not optimal for a particular photograph. Almost all images scanned from film and posted on our site will require some color correction before use in publications. Batch color correction has been performed on some, but not all, digital camera images. Most of the files posted to the web are saved in a lossy JPG format, which also can degrade the quality of the image, but makes it much quicker to download. Scientists needing high levels of quality control for using a photograph as digital data for remote sensing should contact us to request technical scanning of a particular film photograph, or extraction of a TIF file from the original downlinked digital photograph. Publishers and commercial interests needing higher quality images should contact the JSC Media Resource Center.

How are digital camera images compressed and brought down from orbit?

Ever since the implementation of the Kodak DCS460 on Shuttle and Station, the majority of digital photographs have been downlinked while the crew is still in orbit via the Ku-band. Images can also be downloaded from the cameras and brought down on a laptop memory card. Most images come down in a Kodak proprietary format (KDK) and are archived by NASA. The files are then extracted and converted into jpgs for web-based browsing and distribution and posted on our website. We post a full resolution (full size) version, and a reduced resolution (small size) jpg. The jpg parameters used are relatively lossy, so there can be some degradation of the image that is visible to the naked eye, however the full-resolution jpgs are still generally suited to print publication or online display without obvious effects. There are a handful of exceptions where crews downlinked jpgs made on orbit before Ku-band was active on ISS, or where other cameras and formats have been used. We often work with scientists that are interested in using the data for image analysis and remote sensing applications, and we always recommend that they start with a tif file that has been extracted from the original downlinked KDK file. These are available on request from us. Any time a scientist requests such an image, we add it to the list of available images.

What kind of color correction is used on images taken with a digital camera?

The images in our database represent an agglomeration of sources--some of which have included color correction and some have not. For example, some space station expeditions (ISS-4 and ISS-5) photographed a color card on orbit and this was used to develop a color correction algorithm that could be applied to the images on the ground. All of the above processes are somewhat outside the control of the Earth Sciences and Image Analysis Laboratory and apply equally to photographs of Earth and photographs of other subjects. We do hand color correction only for a very few images that are posted with captions to collections such as Earth Observatory or Earth from Space. To get publication-quality results you will probably need to adjust the color balance and contrast for most images downloaded from our site. For scientists that are interested in the spectral content of the image, we recommend requesting that we provide you with a file that has been extracted from the archive file and has not had any color correction.

Can I get a copy of an image at 300 dpi?

The units dpi represent the dots per inch that are displayed when an image is printed. Depending on the scanning routine we used and the software you use, when you open images from our website they may say anyting from 1 dpi to 1000 dpi. However, you can use your software to change this "without resampling" and then print the image at the resolution you want from your printer (which is ofter 300 dpi for photo printers). To determine the size of a particular file when you print it at 300 dpi, take the number of pixels in width, divide by 300 and you will get the width of the photo in inches when printed at 300 dpi. You can do the same for the height of the photo.

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