| 1 | /*
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| 2 | * jdsample.c
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| 3 | *
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| 4 | * Copyright (C) 1991-1996, Thomas G. Lane.
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| 5 | * This file is part of the Independent JPEG Group's software.
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| 6 | * For conditions of distribution and use, see the accompanying README file.
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| 7 | *
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| 8 | * This file contains upsampling routines.
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| 9 | *
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| 10 | * Upsampling input data is counted in "row groups". A row group
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| 11 | * is defined to be (v_samp_factor * DCT_scaled_size / min_DCT_scaled_size)
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| 12 | * sample rows of each component. Upsampling will normally produce
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| 13 | * max_v_samp_factor pixel rows from each row group (but this could vary
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| 14 | * if the upsampler is applying a scale factor of its own).
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| 15 | *
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| 16 | * An excellent reference for image resampling is
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| 17 | * Digital Image Warping, George Wolberg, 1990.
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| 18 | * Pub. by IEEE Computer Society Press, Los Alamitos, CA. ISBN 0-8186-8944-7.
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| 19 | */
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| 20 |
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| 21 | #define JPEG_INTERNALS
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| 22 | #include "jinclude.h"
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| 23 | #include "jpeglib.h"
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| 24 |
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| 25 |
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| 26 | /* Pointer to routine to upsample a single component */
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| 27 | typedef JMETHOD(void, upsample1_ptr,
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| 28 | (j_decompress_ptr cinfo, jpeg_component_info * compptr,
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| 29 | JSAMPARRAY input_data, JSAMPARRAY * output_data_ptr));
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| 30 |
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| 31 | /* Private subobject */
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| 32 |
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| 33 | typedef struct {
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| 34 | struct jpeg_upsampler pub; /* public fields */
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| 35 |
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| 36 | /* Color conversion buffer. When using separate upsampling and color
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| 37 | * conversion steps, this buffer holds one upsampled row group until it
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| 38 | * has been color converted and output.
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| 39 | * Note: we do not allocate any storage for component(s) which are full-size,
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| 40 | * ie do not need rescaling. The corresponding entry of color_buf[] is
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| 41 | * simply set to point to the input data array, thereby avoiding copying.
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| 42 | */
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| 43 | JSAMPARRAY color_buf[MAX_COMPONENTS];
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| 44 |
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| 45 | /* Per-component upsampling method pointers */
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| 46 | upsample1_ptr methods[MAX_COMPONENTS];
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| 47 |
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| 48 | int next_row_out; /* counts rows emitted from color_buf */
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| 49 | JDIMENSION rows_to_go; /* counts rows remaining in image */
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| 50 |
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| 51 | /* Height of an input row group for each component. */
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| 52 | int rowgroup_height[MAX_COMPONENTS];
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| 53 |
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| 54 | /* These arrays save pixel expansion factors so that int_expand need not
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| 55 | * recompute them each time. They are unused for other upsampling methods.
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| 56 | */
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| 57 | UINT8 h_expand[MAX_COMPONENTS];
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| 58 | UINT8 v_expand[MAX_COMPONENTS];
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| 59 | } my_upsampler;
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| 60 |
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| 61 | typedef my_upsampler * my_upsample_ptr;
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| 62 |
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| 63 |
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| 64 | /*
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| 65 | * Initialize for an upsampling pass.
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