Alpha interpolation hint key. The ALPHA_INTERPOLATION hint is a general hint that provides a high level recommendation as to whether to bias alpha blending algorithm choices more for speed or quality when evaluating tradeoffs.

This hint could control the choice of alpha blending calculations that sacrifice some precision to use fast lookup tables or lower precision SIMD instructions. This hint could also control whether or not the color and alpha values are converted into a linear color space during the calculations for a more linear visual effect at the expense of additional per-pixel calculations.

The allowable values for this hint are

• VALUE_ALPHA_INTERPOLATION_SPEED
• VALUE_ALPHA_INTERPOLATION_QUALITY
• VALUE_ALPHA_INTERPOLATION_DEFAULT

Antialiasing hint key. The ANTIALIASING hint controls whether or not the geometry rendering methods of a Graphics2D object will attempt to reduce aliasing artifacts along the edges of shapes.

A typical antialiasing algorithm works by blending the existing colors of the pixels along the boundary of a shape with the requested fill paint according to the estimated partial pixel coverage of the shape.

The allowable values for this hint are

• VALUE_ANTIALIAS_ON
• VALUE_ANTIALIAS_OFF
• VALUE_ANTIALIAS_DEFAULT

Color rendering hint key. The COLOR_RENDERING hint controls the accuracy of approximation and conversion when storing colors into a destination image or surface.

When a rendering or image manipulation operation produces a color value that must be stored into a destination, it must first convert that color into a form suitable for storing into the destination image or surface. Minimally, the color components must be converted to bit representations and ordered in the correct order or an index into a color lookup table must be chosen before the data can be stored into the destination memory. Without this minimal conversion, the data in the destination would likely represent random, incorrect or possibly even unsupported values. Algorithms to quickly convert the results of rendering operations into the color format of most common destinations are well known and fairly optimal to execute.

Simply performing the most basic color format conversion to store colors into a destination can potentially ignore a difference in the calibration of the ColorSpace of the source and destination or other factors such as the linearity of the gamma correction. Unless the source and destination ColorSpace are identical, to correctly perform a rendering operation with the most care taken for the accuracy of the colors being represented, the source colors should be converted to a device independent ColorSpace and the results then converted back to the destination ColorSpace. Furthermore, if calculations such as the blending of multiple source colors are to be performed during the rendering operation, greater visual clarity can be achieved if the intermediate device independent ColorSpace is chosen to have a linear relationship between the values being calculated and the perception of the human eye to the response curves of the output device.

The allowable values for this hint are

• VALUE_COLOR_RENDER_SPEED
• VALUE_COLOR_RENDER_QUALITY
• VALUE_COLOR_RENDER_DEFAULT

Dithering hint key. The DITHERING hint controls how closely to approximate a color when storing into a destination with limited color resolution.

Some rendering destinations may support a limited number of color choices which may not be able to accurately represent the full spectrum of colors that can result during rendering operations. For such a destination the DITHERING hint controls whether rendering is done with a flat solid fill of a single pixel value which is the closest supported color to what was requested, or whether shapes will be filled with a pattern of colors which combine to better approximate that color.

The allowable values for this hint are

• VALUE_DITHER_DISABLE
• VALUE_DITHER_ENABLE
• VALUE_DITHER_DEFAULT

Font fractional metrics hint key. The FRACTIONALMETRICS hint controls whether the positioning of individual character glyphs takes into account the sub-pixel accuracy of the scaled character advances of the font or whether such advance vectors are rounded to an integer number of whole device pixels. This hint only recommends how much accuracy should be used to position the glyphs and does not specify or recommend whether or not the actual rasterization or pixel bounds of the glyph should be modified to match.

Rendering text to a low resolution device like a screen will necessarily involve a number of rounding operations as the high quality and very precise definition of the shape and metrics of the character glyphs must be matched to discrete device pixels. Ideally the positioning of glyphs during text layout would be calculated by scaling the design metrics in the font according to the point size, but then the scaled advance width will not necessarily be an integer number of pixels. If the glyphs are positioned with sub-pixel accuracy according to these scaled design metrics then the rasterization would ideally need to be adjusted for each possible sub-pixel origin.

Unfortunately, scaling each glyph customized to its exact subpixel origin during text layout would be prohibitively expensive so a simplified system based on integer device positions is typically used to lay out the text. The rasterization of the glyph and the scaled advance width are both adjusted together to yield text that looks good at device resolution and has consistent integer pixel distances between glyphs that help the glyphs look uniformly and consistently spaced and readable.

This process of rounding advance widths for rasterized glyphs to integer distances means that the character density and the overall length of a string of text will be different from the theoretical design measurements due to the accumulation of a series of small differences in the adjusted widths of each glyph. The specific differences will be different for each glyph, some being wider and some being narrower than their theoretical design measurements. Thus the overall difference in character density and length will vary by a number of factors including the font, the specific device resolution being targeted, and the glyphs chosen to represent the string being rendered. As a result, rendering the same string at multiple device resolutions can yield widely varying metrics for whole strings.

When FRACTIONALMETRICS are enabled, the true font design metrics are scaled by the point size and used for layout with sub-pixel accuracy. The average density of glyphs and total length of a long string of characters will therefore more closely match the theoretical design of the font, but readability may be affected since individual pairs of characters may not always appear to be consistent distances apart depending on how the sub-pixel accumulation of the glyph origins meshes with the device pixel grid. Enabling this hint may be desirable when text layout is being performed that must be consistent across a wide variety of output resolutions. Specifically, this hint may be desirable in situations where the layout of text is being previewed on a low resolution device like a screen for output that will eventually be rendered on a high resolution printer or typesetting device.

When disabled, the scaled design metrics are rounded or adjusted to integer distances for layout. The distances between any specific pair of glyphs will be more uniform on the device, but the density and total length of long strings may no longer match the theoretical intentions of the font designer. Disabling this hint will typically produce more readable results on low resolution devices like computer monitors.

The allowable values for this key are

• VALUE_FRACTIONALMETRICS_OFF
• VALUE_FRACTIONALMETRICS_ON
• VALUE_FRACTIONALMETRICS_DEFAULT

Interpolation hint key. The INTERPOLATION hint controls how image pixels are filtered or resampled during an image rendering operation.

Implicitly images are defined to provide color samples at integer coordinate locations. When images are rendered upright with no scaling onto a destination, the choice of which image pixels map to which device pixels is obvious and the samples at the integer coordinate locations in the image are transfered to the pixels at the corresponding integer locations on the device pixel grid one for one. When images are rendered in a scaled, rotated, or otherwise transformed coordinate system, then the mapping of device pixel coordinates back to the image can raise the question of what color sample to use for the continuous coordinates that lie between the integer locations of the provided image samples. Interpolation algorithms define functions which provide a color sample for any continuous coordinate in an image based on the color samples at the surrounding integer coordinates.

The allowable values for this hint are

• VALUE_INTERPOLATION_NEAREST_NEIGHBOR
• VALUE_INTERPOLATION_BILINEAR
• VALUE_INTERPOLATION_BICUBIC

Rendering hint key. The RENDERING hint is a general hint that provides a high level recommendation as to whether to bias algorithm choices more for speed or quality when evaluating tradeoffs. This hint could be consulted for any rendering or image manipulation operation, but decisions will usually honor other, more specific hints in preference to this hint.

The allowable values for this hint are

• VALUE_RENDER_SPEED
• VALUE_RENDER_QUALITY
• VALUE_RENDER_DEFAULT

Stroke normalization control hint key. The STROKE_CONTROL hint controls whether a rendering implementation should or is allowed to modify the geometry of rendered shapes for various purposes.

Some implementations may be able to use an optimized platform rendering library which may be faster than traditional software rendering algorithms on a given platform, but which may also not support floating point coordinates. Some implementations may also have sophisticated algorithms which perturb the coordinates of a path so that wide lines appear more uniform in width and spacing.

If an implementation performs any type of modification or "normalization" of a path, it should never move the coordinates by more than half a pixel in any direction.

The allowable values for this hint are

• VALUE_STROKE_NORMALIZE
• VALUE_STROKE_PURE
• VALUE_STROKE_DEFAULT

Text antialiasing hint key. The TEXT_ANTIALIASING hint can control the use of antialiasing algorithms for text independently of the choice used for shape rendering. Often an application may want to use antialiasing for text only and not for other shapes. Additionally, the algorithms for reducing the aliasing artifacts for text are often more sophisticated than those that have been developed for general rendering so this hint key provides additional values which can control the choices of some of those text-specific algorithms. If left in the DEFAULT state, this hint will generally defer to the value of the regular KEY_ANTIALIASING hint key.

The allowable values for this hint are

• VALUE_TEXT_ANTIALIAS_ON
• VALUE_TEXT_ANTIALIAS_OFF
• VALUE_TEXT_ANTIALIAS_DEFAULT
• VALUE_TEXT_ANTIALIAS_GASP
• VALUE_TEXT_ANTIALIAS_LCD_HRGB
• VALUE_TEXT_ANTIALIAS_LCD_HBGR
• VALUE_TEXT_ANTIALIAS_LCD_VRGB
• VALUE_TEXT_ANTIALIAS_LCD_VBGR

LCD text contrast rendering hint key. The value is an Integer object which is used as a text contrast adjustment when used in conjunction with an LCD text anti-aliasing hint such as VALUE_TEXT_ANTIALIAS_LCD_HRGB.

• Values should be a positive integer in the range 100 to 250.
• A lower value (eg 100) corresponds to higher contrast text when displaying dark text on a light background.
• A higher value (eg 200) corresponds to lower contrast text when displaying dark text on a light background.
• A typical useful value is in the narrow range 140-180.
• If no value is specified, a system or implementation default value will be applied.

The default value can be expected to be adequate for most purposes, so clients should rarely need to specify a value for this hint unless they have concrete information as to an appropriate value. A higher value does not mean a higher contrast, in fact the opposite is true. The correction is applied in a similar manner to a gamma adjustment for non-linear perceptual luminance response of display systems, but does not indicate a full correction for this.

Alpha interpolation hint value -- alpha blending algorithms are chosen by the implementation for a good tradeoff of performance vs. quality.

Alpha interpolation hint value -- alpha blending algorithms are chosen with a preference for precision and visual quality.

Alpha interpolation hint value -- alpha blending algorithms are chosen with a preference for calculation speed.

Antialiasing hint value -- rendering is done with a default antialiasing mode chosen by the implementation.

Antialiasing hint value -- rendering is done without antialiasing.

Antialiasing hint value -- rendering is done with antialiasing.

Color rendering hint value -- perform color conversion calculations as chosen by the implementation to represent the best available tradeoff between performance and accuracy.

Color rendering hint value -- perform the color conversion calculations with the highest accuracy and visual quality.

Color rendering hint value -- perform the fastest color conversion to the format of the output device.

Dithering hint value -- use a default for dithering chosen by the implementation.

Dithering hint value -- do not dither when rendering geometry.

Dithering hint value -- dither when rendering geometry, if needed.

Font fractional metrics hint value -- character glyphs are positioned with accuracy chosen by the implementation.

Font fractional metrics hint value -- character glyphs are positioned with advance widths rounded to pixel boundaries.

Font fractional metrics hint value -- character glyphs are positioned with sub-pixel accuracy.

Interpolation hint value -- the color samples of 9 nearby integer coordinate samples in the image are interpolated using a cubic function in both X and Y to produce a color sample. Conceptually the view of the image is very similar to the view used in the BILINEAR algorithm except that the ramps of colors that connect between the samples are curved and have better continuity of slope as they cross over between sample boundaries.

As the image is scaled up, there are no blocky edges and the interpolation should appear smoother and with better depictions of any edges in the original image than with BILINEAR. As the image is scaled down, even more of the original color samples from the original image will have their color information carried through and represented.

Interpolation hint value -- the color samples of the 4 nearest neighboring integer coordinate samples in the image are interpolated linearly to produce a color sample. Conceptually the image is viewed as a set of infinitely small point color samples which have value only at the centers of integer coordinate pixels and the space between those pixel centers is filled with linear ramps of colors that connect adjacent discrete samples in a straight line.

As the image is scaled up, there are no blocky edges between the colors in the image as there are with NEAREST_NEIGHBOR, but the blending may show some subtle discontinuities along the horizontal and vertical edges that line up with the samples caused by a sudden change in the slope of the interpolation from one side of a sample to the other. As the image is scaled down, more image pixels have their color samples represented in the resulting output since each output pixel recieves color information from up to 4 image pixels.

Interpolation hint value -- the color sample of the nearest neighboring integer coordinate sample in the image is used. Conceptually the image is viewed as a grid of unit-sized square regions of color centered around the center of each image pixel.

As the image is scaled up, it will look correspondingly blocky. As the image is scaled down, the colors for source pixels will be either used unmodified, or skipped entirely in the output representation.

Rendering hint value -- rendering algorithms are chosen by the implementation for a good tradeoff of performance vs. quality.

Rendering hint value -- rendering algorithms are chosen with a preference for output quality.

Rendering hint value -- rendering algorithms are chosen with a preference for output speed.

Stroke normalization control hint value -- geometry may be modified or left pure depending on the tradeoffs in a given implementation. Typically this setting allows an implementation to use a fast integer coordinate based platform rendering library, but does not specifically request normalization for uniformity or aesthetics.

Stroke normalization control hint value -- geometry should be normalized to improve uniformity or spacing of lines and overall aesthetics. Note that different normalization algorithms may be more successful than others for given input paths.

Stroke normalization control hint value -- geometry should be left unmodified and rendered with sub-pixel accuracy.

Text antialiasing hint value -- text rendering is done according to the KEY_ANTIALIASING hint or a default chosen by the implementation.

Text antialiasing hint value -- text rendering is requested to use information in the font resource which specifies for each point size whether to apply VALUE_TEXT_ANTIALIAS_ON or VALUE_TEXT_ANTIALIAS_OFF.

TrueType fonts typically provide this information in the 'gasp' table. In the absence of this information, the behaviour for a particular font and size is determined by implementation defaults.

Note:A font designer will typically carefully hint a font for the most common user interface point sizes. Consequently the 'gasp' table will likely specify to use only hinting at those sizes and not "smoothing". So in many cases the resulting text display is equivalent to VALUE_TEXT_ANTIALIAS_OFF. This may be unexpected but is correct.

Logical fonts which are composed of multiple physical fonts will for consistency will use the setting most appropriate for the overall composite font.

Text antialiasing hint value -- request that text be displayed optimised for an LCD display with subpixels in order from display left to right of B,G,R such that the horizontal subpixel resolution is three times that of the full pixel horizontal resolution (HBGR). This is a much less common configuration than HRGB. Selecting this hint for displays with one of the other LCD subpixel configurations will likely result in unfocused text. See VALUE_TEXT_ANTIALIAS_LCD_HRGB, for more information on when this hint is applied.

Text antialiasing hint value -- request that text be displayed optimised for an LCD display with subpixels in order from display left to right of R,G,B such that the horizontal subpixel resolution is three times that of the full pixel horizontal resolution (HRGB). This is the most common configuration. Selecting this hint for displays with one of the other LCD subpixel configurations will likely result in unfocused text.

Notes:
An implementation when choosing whether to apply any of the LCD text hint values may take into account factors including requiring color depth of the destination to be at least 15 bits per pixel (ie 5 bits per color component), characteristics of a font such as whether embedded bitmaps may produce better results, or when displaying to a non-local networked display device enabling it only if suitable protocols are available, or ignoring the hint if performing very high resolution rendering or the target device is not appropriate: eg when printing.

These hints can equally be applied when rendering to software images, but these images may not then be suitable for general export, as the text will have been rendered appropriately for a specific subpixel organisation. Also lossy images are not a good choice, nor image formats such as GIF which have limited colors. So unless the image is destined solely for rendering on a display device with the same configuration, some other text anti-aliasing hint such as VALUE_TEXT_ANTIALIAS_ON may be a better choice.

Selecting a value which does not match the LCD display in use will likely lead to a degradation in text quality. On display devices (ie CRTs) which do not have the same characteristics as LCD displays, the overall effect may appear similar to standard text anti-aliasing, but the quality may be degraded by color distortion. Analog connected LCD displays may also show little advantage over standard text-antialiasing and be similar to CRTs.

In other words for the best results use an LCD display with a digital display connector and specify the appropriate sub-pixel configuration.

Text antialiasing hint value -- request that text be displayed optimised for an LCD display with subpixel organisation from display top to bottom of B,G,R such that the vertical subpixel resolution is three times that of the full pixel vertical resolution (VBGR). Vertical orientation is very uncommon and probably mainly useful for a physically rotated display. Selecting this hint for displays with one of the other LCD subpixel configurations will likely result in unfocused text. See VALUE_TEXT_ANTIALIAS_LCD_HRGB, for more information on when this hint is applied.

Text antialiasing hint value -- request that text be displayed optimised for an LCD display with subpixel organisation from display top to bottom of R,G,B such that the vertical subpixel resolution is three times that of the full pixel vertical resolution (VRGB). Vertical orientation is very uncommon and probably mainly useful for a physically rotated display. Selecting this hint for displays with one of the other LCD subpixel configurations will likely result in unfocused text. See VALUE_TEXT_ANTIALIAS_LCD_HRGB, for more information on when this hint is applied.

Text antialiasing hint value -- text rendering is done without any form of antialiasing.

Text antialiasing hint value -- text rendering is done with some form of antialiasing.