Digital Eye's Snapshot Application

Snapshot is a still video image acquisition program to be used in conjunction with the Digital Eye video digitizer.  It allows you to capture, retouch, crop, and save high resolution video images.

The Controls window contains the controls for setting the resolution of the image to be captured, monitoring the input signal, and capturing images.  When an image is captured, it is displayed in an Image window.  After capture, the image can be retouched and cropped before being saved. 

For more specific information, click on the appropriate help section.

Capture Images

The Controls window allows you to set the capture parameters, monitor the input signal, and capture images.  Two sets of radio buttons, one for Resolution and the other for Pixel Depth, allow you to set the parameters for the next image to be captured.  The Capture button initiates the capture of an image with the appropriate resolution.  

Clicking the Monitor button turns the Monitor on and off.  When activated, the Monitor displays a posterized rendering of incoming video images at fifteen frames per second. For improved resolution the Monitor can also display a dithered rendering. If you wish to have the images dithered before being displayed, click the Dither button; the Monitor will slow down to about four frames per second and increase the latency period between image capture and display.   The Monitor can be enlarged by resizing the Controls window.  A larger Monitor will be slower and less responsive than a smaller one.

The Controls window is used for capturing still images. The capture parameters of the image to be grabbed can be set before the capture. 

To set the capture parameters:

	1)  Click on the desired Resolution setting.  You have a choice of three different sizes. The 640 x 480 pixel image will have the highest resolution, but will take up more disk space when saved.

	2)  Click on the desired Pixel Depth setting. The number of bits per pixel corresponds to the number of shades of gray with which the image is captured. Eight bits corresponds to 256 shades of gray, while four bits corresponds to 16 shades of gray. In other words, an image captured with eight bits per pixel will take up twice as much disk space when saved as one captured with four bits per pixel, but will resolve 16 times as many shades of gray. The difference between four and eight bit images may not be immediately apparent on the MegaPixel Display because it is limited to two bits per pixel (four shades of gray).

To capture an image:

	1)  Click the Capture button. The image will be displayed in the main Image window. If there are no Image windows open, a new one will be created.  If the main  Image window already contains an image, the old image will be replaced by the new one; so be sure to save the previous image, if desired, before capturing a new one.

All captured images are displayed in Image windows.  These can be created by choosing New from the Window menu or by opening a previously saved image. The title bar of the window contains the name and path of the file that the image has been saved to or opened from and the size and number of bits per pixel of the image. If the Image window does not contain an image, its title bar will display a default title.

Only the image in the main Image window will be affected by any menu or window options such as Save or Retouch. The main  Image window will be the only Image window with either a dark gray or black title bar. To select an  Image window simply click on it.

At the bottom right of the window are five buttons.  The image displayed in the Image window can be rescaled by clicking on one of the zoom buttons at the right of this array.  The zoom buttons will either expand or contract the image by a constant zoom factor.  You can also set the amount of scaling directly by typing in the percent scale field.  The magnifier button will rescale the image so that the selected region will occupy as much of the window as possible.  The justify button to the left of the magnifier will rescale the image so that all of it fits within the window.

The button on the far left is the crop button.  Clicking this will display crop lines over the image.  These lines show what part of the image will be cropped off when you either save or print the image.  You can adjust these lines by clicking on one of the handles and dragging it to the desired position.  You can hide these lines by clicking on the crop button again.

Print

To print the image in the main  Image window, choose the Print... from the main menu.  A Print panel will appear.  You can choose to print the image in either Portrait or Landscape mode.  The image will be printed out the same size as it appears on the screen (not 25% larger) unless you choose the Scale to Fit option, in which case the image will be scaled so that it fills the entire page (less margins).  If you have selected a region of the image, the Selection switch will be highlighted to indicate that only the selected region will be printed.  If you wish to print the whole image, click the Selection switch so that it is no longer highlighted.  When you print an image (not a selection), only the area inside the crop lines will be printed.

Retouch 

The Retouch panel can be used to retouch the image in the main Image window.  It consists of three slider controls: contrast, brightness, and curvature adjust.  The curve at the top of the Retouch panel is a graph of the transfer function from the original image's gray scale to that of the retouched image.  The horizontal axis represents the original image's gray scale from black to white.  The vertical axis represents the retouched image's gray scale from black to white.  The columns of grays to the right of the graph represent this relationship in a more intuitive manner.  The far right column contains the gray range of the original image and the left column, the grays that the original range is mapped into. 

The transfer function curve and the gray scale columns are tools designed to help you visualize how changes in contrast, brightness and transfer function curvature will affect the gray scale shading in your captured image.  When you move one of the sliders, the shape of the transfer function curve changes accordingly and the column indicating the new gray scale transitions is modified accordingly.  Changes are not registered on the image in question until the Apply button is clicked.

To retouch an image:

	1)  Choose Retouch... from the Edit menu.  The Retouch panel will appear.

	2)  The sliders on the panel can be manipulated directly or by clicking the icons to either side of the slider.  Clicking on the left icon will move the slider left and clicking on the right icon will move the slider right.  Clicking one of these icons while holding down the Alternate key will return that slider to its center position.  Clicking the Default button will return all of the sliders to their center positions.	

The top slider can be used to adjust the contrast of the image.  Sliding it right will increase contrast while sliding it left will decrease contrast.  The middle slider can be used to adjust the brightness of the image.  Sliding it right will increase brightness while sliding it left will decrease brightness.  The bottom slider controls the shape of the transfer function curve.  Sliding it right will make the curve more convex while sliding it left will make the curve more concave.  A convex curve will tend to make images look brighter, while a concave curve will tend to make images look darker.

	3)  After you have set the desired transfer function, click the Apply button to apply that transfer function to the image in the currently selected Image window.  The transfer function always applies to the original image.  Thus if an image is retouched again, the transfer function will not apply to what you see on the screen, but to what was originally captured.  Retouched images can be saved, in which case the original image is lost (unless previously saved) and any further enhancements will apply to this new image.

Saving Images

To save the image in the main Image window, choose either  the Save TIFF or Save EPS option in the Image menu.  A Save panel appears for you to specify the location where the image will be saved on disk.  You may save images only to directories where you have write permission.  When you save an image, only the region inside the crop lines will be saved.

If you want to save a selected region of an image, choose Save As... from the Image menu.  A save panel will appear; click the Whole Image button so that it now reads "Selection."  Now only the enclosed region will be saved.  To enclose a specific region of an image, simply click on the image and then drag the mouse until the dashed rectangle encloses the desired region.

The Save As... option can also be used to save images in compressed format.  Use the popup button to select the type of compression you desire, either JPEG or LZW.  The JPEG format will yield better compression ratios, but may result in a slight loss in image quality.  See the NeXT Technical Documentation for more information on these compression formats.  Compression can only be used when saving to TIFF files.  

Instead of compressing an image, you could dither it to a 2 bit image.  Normally images are saved at the pixel depth they are captured at (either four or eight bits per pixel) with the dimensions they were captured at (640 x 480, 320 x 240 or 160 x 120 pixels).  When you select either "Dither to 2 bits" or "Dither to 2 bits and LZW," the image will be dithered into a bitmap of two bits per pixel which has the same dimensions as the image displayed on the screen.  Thus if you enlarge (shrink) the image by resizing its window and then save it into two bit format, the saved bitmap will be that much larger (smaller).  If the dither and LZW option is chosen, the dithered image will be compressed using the LZW format.

If you just wish to copy an image, or portion of an image, to the pasteboard without actually saving the image, use the Copy or Copy 2 Bit option in the Edit menu.  Once the  image is on the pasteboard, you can paste it into other applications that accept either TIFF or EPS from the pasteboard.

If you try to close an image which has been modified in any way, or if you try to quit Snapshot without saving changes, an alert panel will appear prompting you to save the changes.

Opening Images

To open an image that has been saved, choose the Open... option from the Image menu.  An Open panel appears where you may locate and select images that are to be opened.  Any number of images may be opened simultaneously.  If an image cannot be opened for some reason, an alert panel appears to notify you of the problem.

Preferences panel

The Preferences panel allows you to set certain parameters of the Image window.  You can set the default crop settings for each window by typing in the desired percent crop along each side of the image.  This will apply to all new Image windows.  This is useful if you have a video camera that produces a known amount of blanking along the edge which you wish cropped off of every image.  By clicking on the Current button, the crop settings of the main Image window will be used as the default crop settings.  You can also adjust the color of the crop lines and/or the border around the image.

The Preferences panel also allows you to set the location that you wish the first Image window to appear at.  You can type in the coordinates of the upper left hand corner of this window.  New Image windows will appear atop the first one offset to the right and towards the bottom of the monitor.

The zoom percentage controls how much an image will rescale by when you zoom in and out using the zoom buttons at the bottom of the Image Window.  When the Show Crop switch is selected, each new Image window will display its crop lines as the default option.

Any changes that you have registered in the Preferences panel will only take affect when you click on the Set button.  If you click Cancel, the changes are ignored.  All saved changes are remember the next time you reboot Snapshot.