About Image Captures

The capture of pixel or vector images is based on the current viewer in the current active tab.

Therefore:

  • To capture several viewers in a single tab, you must use the Full screen capture mode.
  • To record interactions from several viewers in a single tab, you must use the Screen area mode.

The following sub-sections are detailed:

This page discusses:

See Also
Capturing Simple Images

Pixel Images

Pixel images are captured when the Rasterization mode is selected in the Rendering tab of the Options dialog box.

  • If the visualization mode has been switched to Hidden Line Removal (through the All Commands category of the Commands tab) to improve performance, pixel images are captured by replacing Hidden Line Removal by Dynamic hidden line removal (available in the View Mode Customization dialog box).

    In this case, the two rendering styles give very similar results, the only difference being that Dynamic hidden line removal is a lot faster. To avoid this replacement and generate a pixel image with the Hidden Line Removal rendering style, you must use the CATPrintRasterNoForcedHRD=1 variable.

  • Cast shadows cannot be captured.

Vector Images

Vector images are captured when the Wireframe mode is selected in the Rendering tab of the Options dialog box.

  • In Shading rendering mode (in which edges are not displayed), capturing vector images is not useful, and produces images that cannot be viewed in the album: you capture only lines and edges in vector mode, not shaded surfaces.
  • Except for the HRD rendering mode, vector images are captured in Shading with Triangles rendering mode.
  • In HRD rendering mode, vector images are captured in real HLR mode and thus, may look rather different from what you see on screen.

Constant Size Capture

When capturing pixel images, you can use the Constant size option available in the Rasterization Options tab of the Options dialog box.

The Constant size option makes the DPI and the resolution increase with the quality (the higher the quality, the higher the DPI and the resolution), so that the captured images always have the same size in millimeters. Therefore, the image size varies depending on whether the Constant size option is selected or not.

When the option is cleared, the size of saved images (in millimeters) increases with the same dpi when the quality increases:

No constant size capture
Pixel nb Size in mm
Low quality Px,Py Sx,Sy
Medium qualityP'x,P'y P'x screen
Highest quality 2000 x 2000 2000 screen
Customized quality Cp Cmm

When the option is selected, the saved images have the same size on paper (in millimeters): the dpi increases with the size in pixels:

Constant size capture
Pixel nb Size in mm
Low quality Px,Py Sx,Sy
Medium qualityP'x,P'ySx,Sy
Highest quality 2000 x 2000 Sx,Sy
Customized quality N/AN/A

Where:

  • Px,Py

    stands for the pixel number for width and height of the image on screen (viewer size).

  • Sx,Sy

    stands for the image size in millimeters for width and height (viewer size).
  • Px < Px' < 2000
  • 2000 screen stands for the size in millimeters of a 2000 pixel image on screen.
  • Cp stands for the pixel number and Cmm stands for the size in millimeters of the Customized quality.

Clipboard

The image size on paper depends on whether the Constant size capture option is selected.

When the Constant size capture option is cleared, the pasted images are always smaller or equal to 1024. This behavior is more useful for office usage:

No constant size capture
Pixel nb Size in mm
Low quality Px,Py 0.4 x Sx,Sy
Medium qualityP'x,P'y (0.4 x Sx,Sy + 1024 screen ) / 2
Highest quality 2000 x 2000 1024 screen
Customized quality Cp Cmm

When the Constant size capture option is selected, images copied to the clipboard have the same size on paper (in millimeters) as when pasted into Excel sheets.

Constant size capture
Pixel nb Size in mm
Low quality Px,Py Sx,Sy
Medium qualityP'x,P'ySx,Sy
Highest quality 2000 x 2000 Sx,Sy
Customized quality N/AN/A

Image Compression

When saving captures images in another format, you can use different methods to compress them.

  • RLE: Run-length encoding is the easiest and fastest compression method. However, it cannot achieve high compression ratios like those of more sophisticated compression algorithms. The compression ratio mainly depends on the contents.

    This method is suitable for images with large uniformly colored areas, typically found in computer graphics. Most bitmap files support run-length encoding (such as TIFF, BMP, etc.).

  • JPEG lossy compression: This method loses information by removing details the human eyes can hardly perceive. The reconstructed image is not identical to the original one. The loss of visible details may be minimized at the expense of the compression factor.

    Typically, you can compress images by a factor of 20 without losing the subjective quality. The lossless JPEG compression is also part of the JPEG file format but is supported by very few applications.

  • LZW: This method is used for GIF and TIFF files and removes redundancies in the picture. The LZW algorithm and the GIF format are both patented. Note that this method is not available.
  • ZLIB: This lossless compression method belongs to the same category as the LZW method. It is used for PNG format which is meant to be a non-patented successor of the GIF format. Note that this method is not available.
  • CCITT/Fax encoding: CCITT Group 3 and CCITT Group 4 are lossless compression methods for black and white (bi-level) images, which are typically scanned images with a great size. These two methods are mainly used for TIFF files.

The table below shows the most appropriate compression method for a specific image type:

Image typeComputer GraphicsPhotographicBi-levelTypical ratio
Compression
Lossy JPEG OKOK20:1
ZLIBOK5:1
CCITT G4 OK15:1
NoneOKOKOK1:1