ImageGear for C and C++ on Linux v20.0 - Updated
API Reference Guide > Core Component API Reference > Core Component Functions Reference > General Image Functions > IG_image_is_signed_set

This function sets a boolean value that specifies whether the image pixel data is signed or unsigned.


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AT_ERRCOUNT ACCUAPI IG_image_is_signed_set(
       HIGEAR hIGear,
       AT_BOOL bSigned


Name Type Description
hIGear HIGEAR HIGEAR handle of image.
bSigned AT_BOOL Indicates whether the image should be treated as signed or unsigned.

Return Value:

Returns 0 if successful. Otherwise, returns the number of ImageGear errors that occurred during this function call.

Supported Raster Image Formats:

All pixel formats supported by ImageGear for C and C++, except:


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AT_ERRCOUNT nErrcount;  // Number of errors on stack
HIGEAR hIGear;          // Handle of image

// Load image file "picture.bmp" from working directory
nErrcount = IG_load_file("picture.bmp", &hIGear);
if(nErrcount == 0)
    nErrcount = IG_image_is_signed_set(hIGear, TRUE);
    // ...
    // Destroy the image


The Signed flag affects the image display. If an image is unsigned, and does not have any display LUTs attached, pixel intensity value of 0 is the minimal intensity, so it is displayed as black. If the image is signed, 0 is the middle intensity, so it is displayed as 50% gray.

Although ImageGear allows getting and setting the Signed flag from/to images of any colorspaces, except for 1-bit per pixel images, it only takes this flag into account for images that have IG_COLOR_SPACE_ID_Gy colorspace.

Several image file formats, such as DICOM and JPEG2K, allow specifying image pixels as signed or unsigned. If the file format does not specify whether the pixels are signed or unsigned, ImageGear assumes they are unsigned.

If HIGEAR image is signed, and an attempt is made to save it to a file format that does not support Signed images, the Signed flag is ignored.

This function does not modify the image pixel values. It only changes a flag attached to the image. Also, this function does not cause the image to be redrawn. Refer to IG_dspl_image_draw for how to display an image.

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