The Data Item format Bitmap displays a data item as a two dimensional bitmap with the data values encoded as color mappings of the bitmap pixels. This display stype is typically used to illustrate two dimensional histograms. See the histogram decoder section for more information on histograms. The following picture shows a Bitmap display:
The Data Item format dialog box for Bitmap displays looks as follows:
Range
The Bitmap display maps an array item to a two dimensional display. The dimensions of the bitmap are determined by the Range setting. The x-Range determines the width of the bitmap in pixel, the height is the result of the dimension of the array item divided by the x-Range. Say you have an item of dimension 1024 and set the x-Range to 128 the resulting bitmap will be 128 pixel wide and 8 pixel high (The mapping to the horizontal/vertical dimensions can be changed with the Orientation setting). The y-Range is used to map the data values onto colors as outlined in the following paragraph.
Scaling Settings
The scaling section of the Bitmap properties determines how the colors are mapped to the data values. If you select Fixed (y-Range) the entire y-Range is mapped to the available 256 colors. Say your y-Range is 0..100 and your data value is 10 you would see a pixel with about 10% 'intensity'. This setting will keep a constant mapping of colors to values, depending on the y-Range and the color mapping.
Sometimes it may be desirable to have a relative mapping, that is the largest value on the display should be displayed with the 'highest' color, all other values are mapped onto the interval 0 .. largest value. This Auto mode utilizes the entire color mapping. However, the mapping will change depending on the currently largest value on the display. This is an appropriate mode for histograms to display the relative distribution of data.
Palette Settings
The value to color mapping is accomplished with different palettes. Each palette has 256 different colors and the values to be displayed get mapped to that range. Four palettes are available, Linear, Grey-scale, Inverted Grey-scale, and Log. Please refer to the images below for the color mappings. The linear palette distributes the values linearly over the available RGB range, the grey scale uses a linear distribution as well with R=G=B resulting in a grey mapping. The log palette uses a logarithmic distribution to map 0..256 to the resulting RGB values.
Linear palette:
Grey-scale palette:
Log palette:
Sizing Settings
If you choose fixed sizing the dimensions of the bitmap are mapped 1:1 to physical pixels on the screen. In variable mode you can resize the bitmap and it is mapped to physical pixels as appropriate. The fixed sizing mode is useful for getting an undistorted display and may be appropriate for larger bitmaps. The variable mode allows for an arbitrary sizing but might lead to distortions. In Fixed Sizing mode a zoom factor can be selected that will be from 25% to 400% of the original image size.
DMA Mode
Bitmaps have a potentially large amount of pixels (array element items). So performance is critical. If your data block is layed out in a specific format GSEOS can use a very efficient access mechanism (direct memory access) which will speed up the display by several orders of magnitude. It will be automatically enabled when the following conditions are met:
- The data item is an array of 8-bit items with no gap and byte aligned.
- The scaling is Fixed Scaling and the y-range is 0..255.
An indicator in the DMA Mode group notifies you if DMA mode is active or inactive.
