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The number of samples in automatic mode is high to ensure that the algorithm has enough good noise data, even if
finding good samples in a particular image is difficult. In addition, the automatic mode may override the number of
samples you've set if the effect can't find enough good samples. You can vary the size of the samples in either
automatic or manual mode; however, increasing sample size does not guarantee better results, especially if the
resulting samples include more substantial variations in RGB values. Sample size should be reduced if a particular
image doesn't contain sufficiently large areas of constant color values. Conversely, increasing the sample size may
give better results if the image contains large featureless areas.
Repositioning grain or noise samples
Automatic grain or sample selection generally gives acceptable results for the Match Grain or Remove Grain effect,
but you can choose to manually position and resize each sample or change the sample number. For instance, you may
want to reposition samples if the automatic sampling selected a uniform area that is underexposed or overexposed
and that lacks information about grain structure.
Noise samples for the Match Grain and Remove Grain effects are always extracted from the source layer without
regarding any effects or masks that have already been applied to the layer; this results in more accurate sampling. If
you wish to have the samples include the existing effects, you must precompose or prerender the source layer with
all of its effects and then use the result as the source layer to which the grain effect is applied.
You should avoid the following: sharp edges, color gradients, highlights, textures such as grass and water ripples, fine
detail such as hair or tree leaves, and overexposed or underexposed areas lacking in information.
To manually reposition noise samples
In the Effect Controls panel, choose Noise Samples from the Viewing Mode menu. The samples appear as small
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white squares (24 x 24 pixels) overlaid on the source image.
Choose Manual from the Sample Selection pop-up menu in the Sampling controls group.
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To remove the least desirable samples from the image, try reducing the Number Of Samples value.
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To move a noise sample, do one of the following:
•
Click the point parameter
appears in the composition, centered on that sample. Click the desired location in the Composition panel to place
the sample.
•
Using the Selection tool
•
Enter the desired horizontal and vertical coordinates in the Effect Controls panel.
Note: The number of sample points that are enabled corresponds to the current value of the Number Of Samples.
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Repeat for each sample point you want to move.
To change the sampling source frame
The Remove Grain and Match Grain effects take noise samples from the first frame of the sequence by default, but
you can choose to sample the noise from a different frame. This might be useful if there are large lighting or exposure
variations between frames within the sequence.
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Decide which frame you want to sample; make sure that your project settings Display Style is set to Frames,
numbering from zero. The number of the current frame then appears in blue in the top left corner of the Timeline
panel. Enter that frame number as the Source Frame value in the Sampling controls group.
Choose Noise Samples from the Viewing Mode menu.
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The selected frame appears in the Composition panel, and its automatic samples appear on the image.
for the noise sample in the Noise Sample Points controls group. A cross hair
, drag the sample point in the Composition panel to the desired location.
ADOBE AFTER EFFECTS 7.0
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