# <ImageOptions>

The ImagesOptions element specifies options for handling images.

## Full element example

        <ImageOptions>
          <AltText                  value="exclude"/>
          <Images                   value="include"/>
          <ResizeLargeImages        value="yes"/>
          <MaximumWidth             value="144"/>
          <MaximumHeight            value="144"/>
          <ImproveContrast          value="yes"/>
          <Dither                   value="yes"/>
          <Compress                 value="yes"/>
          <LossyLevel               value="none"/>
          <LossyQuality             value="75"/>
          <BitDepth1                value="exclude"/>
          <BitDepth2                value="exclude"/>
          <BitDepth4                value="exclude"/>
          <BitDepth8                value="exclude"/>
          <BitDepth16               value="include"/>
        </ImageOptions>

## Sub-element summary

Tag | Type | Default | Description
--- | --- | --- | ---
`<AltText>` | value | exclude | Whether to include the alternative text of images
`<Images>` | value | include | Whether to include images
`<ResizeLargeImages>` | value | yes | Whether to resize large images
`<MaximumWidth>` | value | 144 | Maximum image width
`<MaximumHeight>` | value | 144 | Maximum image height
`<ImproveContrast>` | value | yes | Whether to improve the image contrast
`<Dither>` | value | yes | Whether to dither images
`<Compress>` | value | yes | Whether to compress images
`<LossyLevel>` | value | none | Types of images to which to apply lossy compression This option requires version 4.0 or later of iSiloX and iSiloXC.
`<LossyQuality>` | value | 75 | Lossy compression image quality. This option requires 4.0 or later of iSiloX and iSiloXC.
`<BitDepth1>` | value | exclude | Whether to include 1-bit versions of images
`<BitDepth2>` | value | exclude | Whether to include 2-bit versions of images
`<BitDepth4>` | value | exclude | Whether to include 4-bit versions of images. Note that before version 4.27 of iSiloX and iSiloXC, the default was include.
`<BitDepth8>` | value | exclude | Whether to include 8-bit versions of images
`<BitDepth16>` | value | include | Whether to include 16-bit versions of images

## Sub-element descriptions

### <AltText>

Description
Set the value attribute of the tag to `include` or `exclude` to respectively include or exclude the alternative text of images.

In an HTML file, references to images often also include alternative text that can be used in place of the image. If you choose not to include images, you are recommended to include the alternative text of images so that images that serve as hyperlinks can still be utilized.
Examples
This example specifies that the alternative text of images should be included.

      <AltText                  value="include"/>

This example specifies that the alternative text of images should not be included.

      <AltText                  value="exclude"/>

### <Images>

Description
Set the value attribute of the tag to `include` or `exclude` to respectively include or exclude images.

This setting applies to root source file images, images referenced through HTML <img> tags, and images that are hyperlink targets. If you include images, you can also set various options for them.
Examples
This example specifies that images should be included.

      <Images                   value="include"/>

This example specifies that images should not be included.

      <Images                   value="exclude"/>

### <ResizeLargeImages>

Description
Set the value attribute of the tag to `yes` or `no` to respectively enable or disable resizing of images larger than the specified maximum width or height as given by the MaximumWidth and MaximumHeight elements.
Examples
This example specifies that images should be resized.

      <ResizeLargeImages        value="yes"/>

This example specifies that images should not be resized.

      <ResizeLargeImages        value="no"/>

### <MaximumWidth>

Description
Set the value attribute of the tag to a positive integer that specifies the maximum width in pixels for images. The value only has an effect on images if image resizing is enabled as specified by the ResizeLargeImages element, in which case, images with a width greater than the specified maximum width are resized so that their resulting width is no greater than the specified maximum width.
Examples
This example specifies a maximum width of 144 pixels for images.

      <MaximumWidth             value="144"/>

This example specifies a maximum width of 304 pixels for images.

      <MaximumWidth             value="304"/>

### <MaximumHeight>

Description
Set the value attribute of the tag to a positive integer that specifies the maximum height in pixels for images. The value only has an effect on images if image resizing is enabled as specified by the ResizeLargeImages element, in which case, images with a height greater than the specified maximum height are resized so that their resulting height is no greater than the specified maximum height.
Examples
This example specifies a maximum height of 144 pixels for images.

      <MaximumHeight            value="144"/>

This example specifies a maximum height of 304 pixels for images.

      <MaximumHeight            value="304"/>

### <ImproveContrast>

Description
Set the value attribute of the tag to `yes` to improve the contrast for black and white and grayscale images. Set the value attribute of the tag to `no` to leave the contrast as it is.
Examples
This example specifies that black and white and grayscale images should have their contrast improved.

      <ImproveContrast          value="yes"/>

This example specifies that the contrast of images should not be changed.

      <ImproveContrast          value="no"/>

### <Dither>

Description
Set the value attribute of the tag to `yes` or `no` to respectively enable or disable dithering of images.

Dithering improves the look of an image when converting it to a lower color bit depth by diffusing the error introduced in lowering the number of colors available for use. Dithering has no effect when the image only consists of colors from the target color bit depth.
Examples
This example specifies that images should be dithered.

      <Dither                   value="yes"/>

This example specifies that images should not be dithered.

      <Dither                   value="no"/>

### <Compress>

Description
Set the value attribute of the tag to `yes` or `no` to respectively enable or disable compression of images. Compressing images generally reduces the space required to store the images, resulting in smaller document sizes.
Examples
This example specifies that images should be compressed.

      <Compress                 value="yes"/>

This example specifies that images should not be compressed.

      <Compress                 value="no"/>

### <LossyLevel>

Description
You can optionally enable lossy compression to significantly reduce the size of the size of converted documents containing images. This type of compression results in the loss of fine detail from the image and so is best applied only to continuous-tone images (i.e., photographs of the real world). Set the value attribute of the tag to one of the following values:

- `none`: Do not apply lossy compression to any images
- `lossy`: Only apply lossy compression to lossy source images only (i.e., JPEG source images)
- `200`: Only apply lossy compression to images with at least 200 unique colors
- `100`: Only apply lossy compression to images with at least 100 unique colors
- `50`: Only apply lossy compression to images with at least 50 unique colors
- `20`: Only apply lossy compression to images with at least 20 unique colors
- `10`: Only apply lossy compression to images with at least 10 unique colors
- `all`: Apply lossy compression to all images

Note that the value attribute of the Compress element must also be set to `yes` to enable lossy compression.
Examples
This example specifies that lossy compression should not be applied to any images.

      <LossyLevel               value="none"/>

This example specifies that lossy compression should be applied to any images with at least 100 unique colors.

      <LossyLevel               value="100"/>

### <LossyQuality>

Description
Set the value attribute of the tag to a value between 1 and 100, inclusive, to specify the quality of images to which lossy compression is applied. The higher the value, the better the image quality, but the lower the compression. The lower the value, the lower the image quality, but the higher the compression.

Note that regardless of the image quality setting, lossy compression applied to an image always results in a reduction in the fidelity of the image. So even an image quality setting of 100 results in a reduction in image fidelity.
Examples
This example sets the quality of lossy compressed images to 90.

      <LossyQuality             value="90"/>

This example sets the quality of lossy compressed images to 48.

      <LossyQuality             value="48"/>

### <BitDepth1>
<BitDepth2>
<BitDepth4>
<BitDepth8>
<BitDepth16>

Description
Set the value attribute of each tag to `include` or `exclude` to respectively include or exclude versions of images at the corresponding bit depth.

If you are creating a document for use on different devices with different types of displays and different versions of Palm OS®, then you may need to include images at more than one color bit depth. If you are creating a document for use on only one device, then it is usually sufficient for you to include images at only one color bit depth. You can include images at the following bit depths:

- 1-bit (black and white)
- 2-bit (four shades of gray)
- 4-bit (16 shades of gray)
- 8-bit (the websafe palette, 256 colors)
- 16-bit (64K colors

Each additional bit depth you include generally increases the size of the resulting document, but not always, because iSiloX and iSiloXC always try to use the lowest possible maximum color bit depth possible for a given image. So even if you include 16-bit images but all your images are pure black and white 1-bit images, iSiloX and iSiloXC will only store 1-bit versions of those images.

The following table lists the Palm OS® versions and the maximum image color bit depths supported.

Palm OS® version | Maximum depth | Notes
--- | --- | ---
3.0/3.1/3.2 | 2-bit | None
3.3 | 4-bit | None
3.5 | 4-bit/8-bit/16-bit | Non-color devices display images at a maximum color depth of 4-bit. The only color device running Palm OS® 3.5 that can display images with 16-bit color is the Visor® Prism.
4.0 | 4-bit/16-bit | Non-color devices display images at a maximum color depth of 4-bit.

The above table may help you decide which color bit depths to include in a document if your audience is wide. One thing you can be sure of is that 1-bit images work across all devices.

On any supported device, regardless of the color depths supported and regardless of what bit depths are included for the images, iSilo™ will still display each image by either choosing the highest supported bit depth of the image or using the closest available colors to display each color of the image. No dithering is applied in the latter case, so the image may not appear as good, but the effect is usually usable.
Examples
This example specifies that only 4-bit and 16-bit versions of images should be included.

      <BitDepth1                value="exclude"/>
      <BitDepth2                value="exclude"/>
      <BitDepth4                value="include"/>
      <BitDepth8                value="exclude"/>
      <BitDepth16               value="include"/>

This example specifies that only 2-bit versions of images should be included.

      <BitDepth1                value="exclude"/>
      <BitDepth2                value="include"/>
      <BitDepth4                value="exclude"/>
      <BitDepth8                value="exclude"/>
      <BitDepth16               value="exclude"/>

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