In the Layer Manager, select the image layer as the current layer. The Layer Properties interface will display image parameter settings, including functional controls for brightness, contrast, transparent color, interpolation method, display method, and stretching of the image layer.

Image Parameters

No Value Settings

• No Value: Refers to values in image data that lack practical significance. Directly enter a pixel value in the text box or click the pick button to select a pixel value in the image layer (snapping supported), setting the specified pixel value as No Value.
• No Value Transparent: This checkbox sets the display color for the specified No Value. When checked, No Value defaults to transparent display. When unchecked, click the drop-down button on the right to select a color from the color panel; pixels with No Value will then display in the specified color.

Background Value Settings

Replace the color of specified background value pixels with another color.

• Background Value: Click the pick button to select a pixel value in the map's image layer as the background value (snapping supported), or directly enter a value in the numeric box.
• Background Value Transparent: Click the drop-down button to set the replacement color in the color panel.

Transparent Color Settings

Transparent color settings configure a specific color in the image layer as transparent, making areas covered by that color transparent. Complete transparent color settings require combining the Transparent Color and Transparent Color Tolerance commands.

• Transparent Color: Check this box to set specified No Value pixels to transparent display; uncheck to display them in the specified color. Click the pick button to select a pixel color in the map's image layer as transparent (snapping supported), or click the drop-down button to choose a color for transparency.
• Transparent Color Tolerance: After setting the tolerance value, assume the original color is (r, g, b) and tolerance is a. Colors requiring transparent display range from (r-a, g-a, b-a) to (r+a, g+a, b+a).

Operation Steps

1. In the Layer Manager, select the image layer for color adjustment and set it as the current layer.
2. Enable transparent color settings for the image layer by checking the Transparent Color checkbox; the color button to the right becomes available.
3. Click the transparent color drop-down button to specify the color for transparency in the image layer.
4. Set the transparent color tolerance: Enter a value directly or click the drop-down button next to the Transparent Color Tolerance numeric box to adjust with the slider. Tolerance values are integers between 0 and 255.
5. After setting, the image layer will display the effect in real time.

Brightness

When the current layer is an image layer, the Brightness numeric box adjusts its brightness. Enter a brightness value directly or click the Brightness box and use the mouse slider to adjust, previewing results in real time.

Contrast

When the current layer is an image layer, the Contrast numeric box adjusts its contrast. Enter a contrast value directly or click the Contrast box and use the mouse slider to adjust, previewing results in real time.

Image Interpolation

When zooming or browsing an image layer, original images map to larger or smaller pixel sets. SuperMap provides five interpolation methods: nearest neighbor, low quality, high quality, high-quality bilinear interpolation, and high-quality bicubic interpolation. Different methods determine display quality, with higher quality requiring longer processing time.

• Nearest Neighbor: A simpler interpolation method with fast processing but the poorest display effects.
• Low Quality: Performs prefiltering to ensure quality during reduction, but enlarged images show poor quality.
• High Quality: Delivers high display quality during zooming but requires longer output time.
• High-Quality Bilinear Interpolation: Uses specified high-quality bilinear interpolation with prefiltering to ensure high-quality display when scaling images.
• High Quality Bicubic: Uses specified high-quality bicubic method with prefiltering for highest-quality display when scaling images.

Display Method

Display Method

Based on the number of bands in image data, display methods differ for single-band and multi-band images. Additionally, modifying display methods is unsupported for image data with bit depths of 32 and 24.

• Single-Band Image
  • Default display: Displays image data without stretching. Uses a color table if available; otherwise, displays in grayscale.

    Figure: Default Display

  • Stretch Display: Adjusts display effects using minimum maximum, standard deviation, Gaussian, or percent clip methods, with options to modify color schemes.

    Figure: Stretch Display

  • Color Table Display: Displays using the image data's color table, allowing color adjustments.

    Figure: Color Table Display

• Multi-Band Image
  • Combination Display: Combines multi-band images via specified vertex colors (e.g., RGB, CMYK) for color display effects, supporting image stretching settings.

    Figure: Combination Display

  • Single Band Stretch Display: Selects a band for display, then applies a stretch method (e.g., minimum maximum, standard deviation, Gaussian, percent clip) to adjust display effects and color schemes.

    Figure: Single Band Standard Deviation Display

  • Single Band Color Table Display: Selects a band for display, allowing color adjustments.

    Figure: Single Band Color Table Display

  • Single Band Grid Function Display: Selects a band for display, applying raster functions to achieve desired display effects.

    Figure: Single Band Grid Function Display

Vertex Color

Different color generation principles distinguish devices like monitors and projectors (using light) from printers and presses (using pigments). SuperMap supports seven color spaces: RGB, CMYK, RGBA, CMY, YIQ, YUV, and YCC.

The vertex color combo box lists supported color spaces for setting image data display modes. Click the drop-down button next to the "color mode:" label and select the desired vertex color. Default is RGB.

Vertex Color	Description
RGB	Primarily used in display systems. RGB abbreviates red, green, blue. Assigns intensity values (0-255) to each pixel's RGB components.
CMYK	Primarily used in printing systems. CMYK stands for cyan, magenta, yellow, black. Mixes pigments by adjusting these base colors, using black for brightness and purity.
RGBA	Primarily used in display systems. RGB abbreviates red, green, blue; A controls transparency.
CMY	Primarily used in printing systems. CMY stands for cyan, magenta, yellow. Mixes pigments by adjusting these base colors.
YIQ	Mainly used in North American TV systems (NTSC).
YUV	Mainly used in European TV systems (PAL).
YCC	Mainly used in JPEG image formats.

Image Color

Layer Properties supports modifying image parameter colors. Click the combo box next to the label control to select a grouped color. Note: Changing image layer colors requires single-band pixel format images (8-bit or 16-bit). Multi-band or composite band image layers cannot change image color.

Image Stretching

During image data acquisition, factors may degrade quality. Stretching improves display effects and clarity, highlighting relevant information while suppressing irrelevant details. Stretching alters brightness and contrast, making features more identifiable.

SuperMap offers stretch types: no stretching, standard deviation, minimum maximum, histogram equalization, histogram specification, Gaussian, and percent clip.

Supports batch setting stretch methods for image layers. In Layer Manager, select multiple image layers and uniformly set the stretch method in Layer Properties for consistent display effects.

• No Stretching: Applies no stretch, but effectively only works for unsigned 8-bit storage format image data. Pixel values display between 0-255. For non-unsigned 8-bit data, SuperMap uses minimum maximum display to fit this range. As shown below, left image is unstretched unsigned 8-bit (dark), right is its red band histogram with values concentrated in low grayscale.

  Figure: No Stretching and Histogram

• Minimum Maximum: Linear extrusion between min and max pixel values, distributing values between [0,255]. Enhances contrast and brightness for better feature identification. Suitable for raster images with dense pixel value distributions.

  As shown below, left image post-stretch is clearer with enhanced contrast; right histogram gray shows pre-stretch, red shows post-stretch.

  Figure: Minimum Maximum and Pre/Post-Stretch Histogram

• Standard Deviation: Trims extreme values and linearly extrudes remaining pixels to increase contrast. Calculates one standard deviation range, updates it based on coefficient, then linearly extrudes values to [0,255], reducing deviation from mean.

  Standard deviation: Square root of variance, reflecting data dispersion. Higher values indicate greater deviation from mean; lower values indicate closer clustering.

  As shown, one standard deviation covers 68% of pixels, two cover 95%, three cover 99%. With coefficient set to 2, pixels beyond two deviations are clipped to 0 or 255; values within are linearly extruded to 0-255. Often brightens dark raster datasets.

  Histogram illustrates this method. Left image shows standard deviation effect; right compares pre/post-stretch histograms. Post-stretch histogram resembles a normal distribution curve with increased deviation (reduced pixel deviation from mean).

  Often brightens dark images.

  Figure: Standard Deviation Stretch and Pre/Post-Stretch Histogram

• Gaussian: Aims to normalize pixel value distribution; Gaussian stretching is linear extrusion.
  • Gaussian Coefficient: Pixel values multiplied by coefficient before stretching to [0,255].
  • Using Median: When checked, stretching uses median as central axis; unchecked, defaults to maximum as axis.
    Note:

    If image lacks statistical information, a dialog prompts: "Stretch method requires statistical data. Calculate and proceed?" Click OK to calculate statistics and apply stretch; click Cancel to switch to no stretching.

• Percent Clip: Assumes most pixels fall within min/max limits. Sets percentages to clip outliers to endpoints, then linearly extrudes remaining values. Excludes histogram tails before applying minimum maximum stretching. Requires setting min/max exclusion percentages.

  Supports per-band stretching for multi-band images. Click the "Histogram" button next to the combo box to open band histograms, specifying min/max exclusion percentages.

  Example: Pixel range [0,100], min/max exclusion set to 10. Percent clip stretches [10,90] to [0,255], with [0,10] clipped to 0 and [90,100] to 255.

  As shown, first image displays without stretch range (histogram shows few low/high values, reducing clarity). Second image excludes endpoints via percent clip, enhancing contrast and clarity.

  Figure 1: No Stretch Range	Figure 2: With Stretch Range

• Histogram Equalization: Non-linear extrusion that redistributes pixel values to equalize counts within grayscale ranges. Enhances mid-range contrast while reducing tail contrast, producing a flatter histogram.

  Figure: Histogram Before/After Equalization (Image Source: Network)

  Figure: Histogram Equalization Stretch and Pre/Post-Stretch Histogram

  Post-equalization, overall contrast is strong. This method trades reduced grayscale levels for increased contrast, potentially losing specific grayscale information. May degrade images with poor original quality, small dynamic range, or highly uneven histogram distribution.

• Histogram Specification: Mathematically transforms lookup tables to match one image's histogram to another. Used as preprocessing for image mosaicking or multi-temporal remote sensing change studies, reducing effects from sun angle or atmospheric differences.

  Similar to histogram equalization, but output is variable (based on imported histogram XML file) rather than fixed.

  Note:

  If image lacks pyramids, a dialog prompts: "Stretch method requires histogram creation. Create and proceed?" when using percent clip, histogram specification, or histogram equalization. Click OK to create histogram and apply stretch; click Cancel to switch to No Stretching.

• Adaptive Stretch: Adaptive stretch (full name: Contrast-Limited Adaptive Histogram Equalization) enhances local contrast by dividing images into sub-regions, computing histograms per region, and redistributing brightness. Improves edge clarity but may amplify noise in uniform areas.

  Traditional adaptive equalization risks excessive noise amplification in uniform regions. Adaptive stretch limits contrast enhancement to reduce this issue.

  Suitable for enhancing local contrast in images. Currently supports 8-bit and 16-bit unsigned data types.

  Handling of No Value areas:

  • Specified No Value areas (e.g., 0 or 255): Identified and excluded; original values retained during processing, unaffected by enhancement.
  • Other areas: Pixel values participate in adaptive stretch. Resulting values within No Value range may cause visual anomalies.

  Requires these parameters:

  • Crop threshold: Limits max pixels per value in histograms to constrain local contrast enhancement, preventing noise amplification or artifacts in flat areas.
  • Tile rows/columns: Specifies number of tiles (total tiles = rows × columns).
    • Higher rows/columns: Smaller sub-regions, finer local enhancement, but may cause blocky artifacts.
    • Lower rows/columns: Larger sub-regions, smoother enhancement, reduced block effects, but weaker small-scale detail enhancement.

Gamma

Gamma parameters non-linearly adjust brightness and contrast to enhance detail and improve display quality. Gamma values range from 0 to 10 (inclusive), with two decimal places precision.

• Gamma = 1: No gamma correction applied.

• Gamma > 1: Increases contrast in dark areas (enhancing detail), but reduces detail in bright areas; overall image brightens.

• Gamma < 1: Increases contrast in bright areas (enhancing detail), but reduces detail in dark areas; overall image darkens.

Figure: Gamma=1	Figure: Gamma=2
Figure: Gamma=1	Figure: Gamma=0.4

Display Orthorectified Image

If the layer's associated dataset contains RPC information, check this box. When checked, displays orthorectified images based on elevation data; unchecked, displays uncorrected images.

When checked, elevation settings include:

• Fixed Value: Default displays elevation from remote image files; edit other values in the text box.
• SRTM V4: Uses elevation data from remote resource packs. Available after image environment deployment.
• Custom: Loads elevation via specified DEM data. SupportsTiff/GeoTIFF,Erdas Image,PCIDSK, andArcInfoGrid formats. Use theAdd Folder button for ArcInfoGrid data.

Related Topics

Setting Layer Common Properties

Setting Vector Layer Properties

Setting Raster Layer Properties