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#99 - show PCA screenshot and chafa reference on README

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Autumn Lamonte 2022-01-28 18:24:06 -06:00
parent 63055fa744
commit b90084576b
3 changed files with 59 additions and 37 deletions
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6
README.md
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@ -28,9 +28,11 @@ stock xterm, with a custom mouse icon, and SGR-Pixel mode active:
![Xterm SGR-Pixel Mouse](/screenshots/xterm_pixel_mouse.gif?raw=true "Xterm SGR-Pixel Mouse")
A new sixel encoder is in the works for Xterm, which should look a lot
better:
better. This encoder is inspired in part by
[chafa's](https://hpjansson.org/chafa/) high-performance principal
component analysis based sixel encoder.
![Xterm Snake Image](/screenshots/snake_xterm_hq.png?raw=true "Xterm Snake Image - HQ Encoder")
![PCA color matching with 128-color palette and translucent windows](/screenshots/pca_match.png?raw=true "PCA color matching with 128-color palette and translucent windows")
Jexer can be run inside its own terminal window, with support for all
of its features including images and mouse, and more terminals:

BIN
screenshots/pca_match.png Normal file
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90
src/jexer/backend/HQSixelEncoder.java
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@ -25,6 +25,12 @@
*
* @author Autumn Lamonte ⚧ Trans Liberation Now
* @version 1
*
* Portions of this encoder were inspired / influenced by Hans Petter
* Jansson's chafa project: https://hpjansson.org/chafa/ . Please refer to
* chafa's high-performance sixel encoder for far more advanced
* implementations of principal component analysis color mapping, and sixel
* row encoding.
*/
package jexer.backend;
@ -36,6 +42,7 @@ import java.awt.image.IndexColorModel;
import java.awt.image.Raster;
import java.io.FileInputStream;
import java.util.ArrayList;
import java.util.BitSet;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
@ -48,6 +55,14 @@ import jexer.bits.MathUtils;
* HQSixelEncoder turns a BufferedImage into String of sixel image data,
* using several strategies to produce a reasonably high quality image within
* sixel's ~19.97 bit (101^3) color depth.
*
* <p>
* Portions of this encoder were inspired / influenced by Hans Petter
* Jansson's chafa project: https://hpjansson.org/chafa/ . Please refer to
* chafa's high-performance sixel encoder for far more advanced
* implementations of principal component analysis color mapping, and sixel
* row encoding.
* </p>
*/
public class HQSixelEncoder implements SixelEncoder {
@ -485,6 +500,25 @@ public class HQSixelEncoder implements SixelEncoder {
}
};
/**
* Metadata regarding one sixel row.
*/
private class SixelRow {
/**
* A set of colors that are present in this row.
*/
private BitSet colors;
/**
* Public constructor.
*/
public SixelRow() {
colors = new BitSet(sixelColors.size());
}
}
/**
* Number of colors in this palette.
*/
@ -581,6 +615,11 @@ public class HQSixelEncoder implements SixelEncoder {
*/
private ArrayList<Bucket> buckets;
/**
* The sixel rows of this image.
*/
private SixelRow [] sixelRows;
/**
* If true, quantization is done.
*/
@ -620,6 +659,10 @@ public class HQSixelEncoder implements SixelEncoder {
numColors = Math.min(paletteSize, FAST_AND_DIRTY);
}
sixelColors = new ArrayList<Integer>(numColors);
sixelRows = new SixelRow[(image.getHeight() / 6) + 1];
for (int i = 0; i < sixelRows.length; i++) {
sixelRows[i] = new SixelRow();
}
if (image.getTransparency() == Transparency.TRANSLUCENT) {
// PNG like images where transparency is carried in alpha.
@ -1226,7 +1269,8 @@ public class HQSixelEncoder implements SixelEncoder {
* . The palette colors have been sorted by their principal
* component (see principal component analysis), such that a binary
* search can quickly find the region where the closest matching
* color resides.
* color resides. One can then search forward and backward to find
* all nearby colors.
*
* @param red the red component, from 0-100
* @param green the green component, from 0-100
@ -1457,7 +1501,9 @@ public class HQSixelEncoder implements SixelEncoder {
int height = sixelImageHeight;
int width = sixelImageWidth;
SixelRow sixelRow;
for (int imageY = 0; imageY < height; imageY++) {
sixelRow = sixelRows[imageY / 6];
for (int imageX = 0; imageX < width; imageX++) {
int oldPixel = rgbArray[imageX + (width * imageY)];
if ((oldPixel & 0xFF000000) != 0xFF000000) {
@ -1478,6 +1524,7 @@ public class HQSixelEncoder implements SixelEncoder {
assert (colorIdx < sixelColors.size());
int newPixel = sixelColors.get(colorIdx);
rgbArray[imageX + (width * imageY)] = colorIdx;
sixelRow.colors.set(colorIdx);
if (quantizationType == 0) {
// For direct map, every possible color is already in
@ -1763,41 +1810,11 @@ public class HQSixelEncoder implements SixelEncoder {
// Render the entire row of cells.
int width = bitmap.getWidth();
// TODO: sixels[][] shouldn't be necessary, and both of these loops
// should be able to be combined.
int [][] sixels = new int[width][6];
for (int currentRow = 0; currentRow < fullHeight; currentRow += 6) {
Palette.SixelRow sixelRow = palette.sixelRows[currentRow / 6];
// See which colors are actually used in this band of sixels.
boolean [] usedColors = new boolean[palette.sixelColors.size()];
for (int imageX = 0; imageX < width; imageX++) {
for (int imageY = 0;
(imageY < 6) && (imageY + currentRow < fullHeight);
imageY++) {
int colorIdx = rgbArray[imageX +
(width * (imageY + currentRow))];
if (allowTransparent && (colorIdx == -1)) {
sixels[imageX][imageY] = colorIdx;
continue;
}
/*
if (!palette.noDither) {
assert (colorIdx >= 0);
assert (colorIdx < palette.sixelColors.size());
}
if (!allowTransparent) {
assert (colorIdx != -1);
}
*/
sixels[imageX][imageY] = colorIdx;
usedColors[colorIdx] = true;
}
}
for (int i = 0; i < usedColors.length; i++) {
if (!usedColors[i]) {
for (int i = 0; i < paletteSize; i++) {
if (!sixelRow.colors.get(i)) {
continue;
}
@ -1811,12 +1828,15 @@ public class HQSixelEncoder implements SixelEncoder {
for (int imageX = 0; imageX < width; imageX++) {
// Add up all the pixels that match this color.
// TODO: Make this scan horizontally first to build the
// row, so as to reduce all the random access.
int data = 0;
for (int j = 0;
(j < 6) && (currentRow + j < fullHeight);
j++) {
if (sixels[imageX][j] == i) {
if (rgbArray[imageX + (width * (currentRow + j))] == i) {
switch (j) {
case 0:
data += 1;