QuickTime 4 Reference

Source Color Limits

The sourceMinimum and sourceMaximum fields in a color component's gxTransferComponent structure define the allowable range of values for source color in that component. Color values outside of the range cause no drawing to occur. If sourceMaximum is less than sourceMinimum , the range allowed consists of values less than sourceMaximum or greater than sourceMinimum . Figure 52 shows the effect of sourceMinimum and sourceMaximum on drawing using blend mode.

Figure 52 The effect of source color limits on drawing

Note in Figure 52 that, when sourceMinimum is less than sourceMaximum , only the cloud in the source image is within the source limits, so only the cloud is blended with the destination image to create the result. Conversely, when sourceMaximum is less than sourceMinimum , the cloud in the source image is outside the source limits, so it is the only part of the source that is not blended with the destination image when creating the result.