How to use the color palette to change the PNG Image Format

This algorithm directly reads and modifies the color palette of images in PNG format by referring to an article from an expert, and then generates a new color palette to replace the original one.

In this way, the effects of common color changes in the game can be solved, and the game capacity is limited, so it cannot store too many genie images.

The specific process is not complex. You can search for information first and see the format definition of the PNG image. This algorithm finds the color palette and generates a new CRC check code based on the original format, and then replaces the original color palette. In this way, you can use a PNG Image to create multiple color copies.

 

Public class palettedimage {<br/> public image getpalettedimage (byte [] data, int [] originalcolors, <br/> int [] palettedcolors) {<br/> byte [] tempdata = new byte [data. length]; <br/> system. arraycopy (data, 0, tempdata, 0, Data. length); <br/> image IMG = NULL; <br/> int [] parameter = {<br/> 0, 0, 0 }; <br/> analyze (tempdata, parameter); <br/> for (INT I = 0; I <originalcolors. length; I ++) {<br/> r Eplacecolor (tempdata, parameter, originalcolors [I], <br/> palettedcolors [I]); <br/> <br/>}< br/> filldata (tempdata, parameter); <br/> try {<br/> IMG = image. createimage (tempdata, 0, Data. length); <br/> <br/>}< br/> catch (exception e) {<br/> system. out. println ("getpalettedimage &" + E. tostring (); <br/> <br/>}< br/> return IMG; <br/> <br/>}</P> <p> private void analyze (byte [] data, int [] Para) {<br/> int offset = 8; <br/> int chunklen = 0; <br/> while (data [Offset + 4]! = 0x50 | data [Offset + 5]! = 0x4c <br/> | data [Offset + 6]! = 0x54 | data [Offset + 7]! = 0x45) {<br/> chunklen = readint (data, offset); <br/> offset ++ = (4 + 4 + chunklen + 4 ); <br/> <br/>}< br/> chunklen = readint (data, offset); <br/> para [2] = chunklen/3; <br/> para [0] = offset + 8; <br/> para [1] = offset + 8 + chunklen; <br/> <br/>}</P> <p> private int readint (byte [] data, int offset) {<br/> return (data [offset] & 0xff) <24) <br/> | (data [Offset + 1] & 0xff) <16) <br/> | (data [Offset + 2] & 0xff) <8) | (data [Offset + 3] & 0xff ); <br/> <br/>}</P> <p> private void replacecolor (byte [] data, int [] para, int oldcolor, <br/> int newcolor) {<br/> byte RR = (byte) (oldcolor> 16) & 0xff); <br/> byte Gg = (byte) (oldcolor> 8) & 0xff); <br/> byte BB = (byte) (oldcolor & 0xff); <br/> for (INT I = 0, offset = para [0], temp = 0; I <para [2]; I ++, <br/> Offset + = 3) {<br/> If (RR = data [offset] & Gg = data [Offset + 1] <br/> & BB = data [Offset + 2]) {<br/> data [offset] = (byte) (newcolor> 16) & 0xff); <br/> data [Offset + 1] = (byte) (newcolor> 8) & 0xff); <br/> data [Offset + 2] = (byte) (newcolor & 0xff); <br/> break; <br/> <br/>}</P> <p> private void filldata (byte [] data, int [] para) {<br/> int checksum = update_crc (data, para [0]-4, para [2] * 3 + 4 ); <br/> data [para [1] = (byte) (checksum> 24) & 0xff ); <br/> data [para [1] + 1] = (byte) (checksum> 16) & 0xff ); <br/> data [para [1] + 2] = (byte) (checksum> 8) & 0xff ); <br/> data [para [1] + 3] = (byte) (checksum) & 0xff ); <br/> <br/>}</P> <p> private int update_crc (byte [] Buf, int off, int Len) {<br/> int C = 0 xffffffff; <br/> int N, K; <br/> int xx; <br/> int [] crc_table = new int [256]; <br/> for (n = 0; n <256; n ++) {<br/> xx = N; <br/> for (k = 0; k <8; k ++) {<br/> If (XX & 1) = 1) {<br/> xx = 0xedb88320 ^ (XX >>> 1 ); <br/> <br/>}< br/> else {<br/> xx = XX >>> 1; <br/> <br/>}< br/> crc_table [N] = xx; <br/> <br/>}< br/> for (n = off; n <Len + off; n ++) {<br/> C = crc_table [(C ^ Buf [N]) & 0xff] ^ (C >>> 8 ); <br/> <br/>}< br/> return (C ^ 0 xffffffff ); <br/> <br/>}</P> <p> <br/>}< br/>

 

The interface is the getpalettedimage () function. You only need to enter the byte array of the original image, the color value to replace the color, and the target color value. Because multiple colors can be replaced at the same time, the input parameter is an array representing the integer color. In short, make sure that the original color exactly corresponds to the target color. The method is simple and practical.