Once you get back home, the first thing you should do is to archive your original image files. Burn them to a CD-ROM or DVD and put it away for safekeeping.

Then open up an image and examine it carefully in IrfanView. Sometimes stuff will show up on a nice big monitor at home that you might have missed when you shot the images at night in the dark.

When viewing the image in IrfanView, information about the image file is shown at the bottom of the display window.

Information Display in IrfanView

The name of the image file is displayed in the bar at the top of the window as well as its current display size in pixels.

In the bar at the bottom of the display window, more information about the image is shown. In this example image, the information from left to right is:

• 3888 x 2592 x 24BPP - This is the true full optical resolution of the image. The pixels dimensions are 3888 pixels by 2592 pixels. 24BPP means it has a color depth of 24 bits per pixel which is also called 8-bit per channel color. Since there are 3 color channels for each pixel, one each for red, green, and blue, 3 channels x 8 bits per channel = 24-bit color. 24-bit color is considered a minimum standard for full-color images.

• 12/40 - This means this image file is the 12th in a directory with 40 files.

• 14% - This is the amount of enlargement for the current display.

• 4.36mb / 28.83mb - This is the size of the JPEG file stored on your hard drive and the size of the file when it is uncompressed and opened up to full resolution.

• 2/25/2009 03:20:51 - This is the date and time that the image was originally taken, or the time and date of the file if it has been modified and saved.

Under the pull-down menus, if you select Image > Information, or just hit the keyboard shortcut of the letter "I", you will find much more information about your image. Of particular use is the EXIF info button. It will display all kinds of information stored in the file about camera settings.

Under the Information dialog, you can also press the IPTC info button and this will allow you to write a caption and store other information inside the image file.

Navigating in IrfanView

You can use the magnifying tool in IrfanView to enlarge the image. Or you can click and drag the cursor over an area and enlarge it. If you hold down the right mouse button in the image, it will turn into a hand that will allow you to drag the image around while magnified to see different parts of it.

Double clicking inside of an image on display will display it full screen at 100 percent enlargement on your desktop. Clicking again one time will advance to the next file in the current directory. You can also use the space bar and backspace, and the left and right arrow keys to display and move through your image files. Use the escape key to get out of full-screen mode and go back to the normal display.

When you are in full screen mode, you can use the left and right mouse buttons to go forward and backwards through the image files in that directory. You can use the arrow keys to move around inside the image if it is larger than the desktop display.

You can use keyboard shortcuts while the image is in full screen move. The plus and minus keys will magnify and reduce the image size.

Examine the Image

Examine your images carefully for correct exposure, focus, trailing, satellites, lens aberrations and the host of other things that can go wrong. If the problems are really severe, you may have to throw out the bad frames and re-shoot them.

Look to see if your exposure was long enough. This is very important. You do not want the sky background to be completely black. If it is, then all of the faintest detail in your image will be down in the noise of the camera.

Here the image is enlarged to 200 percent to check focus, tracking and noise. Stars are trailed because this was a 15-second exposure on a fixed tripod. The focus looks good, as does the noise. But what is that faint diffuse smudge in the image? That's Comet Lulin!

Enlarge the image to 100 percent at least, and take a look at the stars in the center and corners of the frame. This can be very educational, and it can tell you if your focus and tracking were accurate.

Look at the overall color balance of the image. Long-exposure photos shot with daylight or automatic white balance at sites with light pollution, such as this one above, will usually come out with a red-brown sky. Make a mental note to fix this.

Check the overall brightness and contrast of the image. We can adjust the brightness to a degree, but it is usually much better to have an image that starts out a little too light than too dark. It is easier to lower the brightness of an image. Increasing the brightness usually makes the noise more visible.

Finally, while the image is magnified to 100 or 200 percent, check out the noise in a blank area of sky background.

Image Evaluation - The Bottom Line Always examine your images critically to look for problems. Look for correct exposure, excessive noise, accurate focus and trailing due to tracking errors.