Question

首先，我的问题与How do I convert image to 2-bit per pixel?不同，不幸的是，它的解决方案在我的案例中不起作用......

我需要将图像转换为每像素2位灰度BMP格式。示例图像具有以下属性：

Color Model: RGB
Depth: 4
Is Indexed: 1
Dimension: 800x600
Size: 240,070 bytes (4 bits per pixel but only last 2 bits are used to identify the gray scales as 0/1/2/3 in decimal or 0000/0001/0010/0011 in binary, plus 70 bytes BMP metadata or whatever)

样本BMP图像的开头部分的十六进制值：

3s表示图像开头的白色像素。再往下有一些0s，1s和2s代表黑色，深灰色和浅灰色：

使用以下命令，

convert pic.png -colorspace gray +matte -depth 2 out.bmp

我可以直观正确的4级灰度图像，但每个像素的深度或尺寸错误：

Color Model: RGB
Depth: 8 (expect 4)
Dimension: 800x504
Size: 1,209,738 bytes (something like 3 bytes per pixel, plus metadata)
(no mention of indexed colour space)

请帮忙......

Answer 1

好的，我已经按照Mark的提示编写了一个Python脚本（参见原始问题下的评论），手动创建一个带有4bpp的4级灰度BMP。这种特定的BMP格式结构适用于WaveShare制造的4.3英寸电子纸显示模块。规格可以在这里找到：http://www.waveshare.com/wiki/4.3inch_e-Paper

以下是如何将原始图像传输到我的代码并保存结果。

convert in.png -colorspace gray +matte -colors 4 -depth 2 -resize '800x600>' pgm:- | ./4_level_gray_4bpp_BMP_converter.py > out.bmp

4_level_gray_4bpp_BMP_converter.py的内容：

#!/usr/bin/env python

"""

### Sample BMP header structure, total = 70 bytes
### !!! little-endian !!!

Bitmap file header 14 bytes
42 4D          "BM"
C6 A9 03 00    FileSize = 240,070       <= dynamic value
00 00          Reserved
00 00          Reserved
46 00 00 00    Offset = 70 = 14+56

DIB header (bitmap information header)
BITMAPV3INFOHEADER 56 bytes
28 00 00 00    Size = 40
20 03 00 00    Width = 800              <= dynamic value
58 02 00 00    Height = 600             <= dynamic value
01 00          Planes = 1
04 00          BitCount = 4
00 00 00 00    compression
00 00 00 00    SizeImage
00 00 00 00    XPerlPerMeter
00 00 00 00    YPerlPerMeter
04 00 00 00    Colours used = 4
00 00 00 00    ColorImportant
00 00 00 00    Colour definition index 0
55 55 55 00    Colour definition index 1
AA AA AA 00    Colour definition index 2
FF FF FF 00    Colour definition index 3

"""

# to insert File Size, Width and Height with hex strings in order
BMP_HEADER = "42 4D %s 00 00 00 00 46 00 00 00 28 00 00 00 %s %s 01 00 04 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 04 00 00 00 00 00 00 00 00 00 00 00 55 55 55 00 AA AA AA 00 FF FF FF 00"
BMP_HEADER_SIZE = 70
BPP = 4
BYTE = 8
ALIGNMENT = 4 # bytes per row

import sys
from re import findall

DIMENTIONS = 1
PIXELS = 3

BLACK     = "0"
DARK_GRAY = "1"
GRAY      = "2"
WHITE     = "3"

# sample data:
# ['P5\n', '610 590\n', '255\n', '<1 byte per pixel for 4 levels of gray>']
# where item 1 is always P5, item 2 is width heigh, item 3 is always 255, items 4 is pixels/colours
data = sys.stdin.readlines()

width = int(data[DIMENTIONS].strip().split(' ')[0])
height = int(data[DIMENTIONS].strip().split(' ')[1])


if not width*height == len(data[PIXELS]):
    print "Error: pixel data (%s bytes) and image size (%dx%d pixels) do not match" % (len(data[PIXELS]),width,height)
    sys.exit()

colours = [] # enumerate 4 gray levels
for p in data[PIXELS]:
    if not p in colours:
        colours.append(p)
        if len(colours) == 4:
            break

# it's possible for the converted pixels to have less than 4 gray levels

colours = sorted(colours) # sort from low to high

# map each colour to e-paper gray indexes
# creates hex string of pixels
# e.g. "0033322222110200....", which is 4 level gray with 4bpp

if len(colours) == 1: # unlikely, but let's have this case here
    pixels = data[PIXELS].replace(colours[0],BLACK)
elif len(colours) == 2: # black & white
    pixels = data[PIXELS].replace(colours[0],BLACK)\
                         .replace(colours[1],WHITE)
elif len(colours) == 3:
    pixels = data[PIXELS].replace(colours[0],DARK_GRAY)\
                         .replace(colours[1],GRAY)\
                         .replace(colours[2],WHITE)
else: # 4 grays as expected
    pixels = data[PIXELS].replace(colours[0],BLACK)\
                         .replace(colours[1],DARK_GRAY)\
                         .replace(colours[2],GRAY)\
                         .replace(colours[3],WHITE)

# BMP pixel array starts from last row to first row
# and must be aligned to 4 bytes or 8 pixels
padding = "F" * ((BYTE/BPP) * ALIGNMENT - width % ((BYTE/BPP) * ALIGNMENT))
aligned_pixels = ''.join([pixels[i:i+width]+padding for i in range(0, len(pixels), width)][::-1])

# convert hex string to represented byte values
def Hex2Bytes(hexStr):
    hexStr = ''.join(hexStr.split(" "))
    bytes = []
    for i in range(0, len(hexStr), 2):
        byte = int(hexStr[i:i+2],16)
        bytes.append(chr(byte))
    return ''.join(bytes)

# convert integer to 4-byte little endian hex string
# e.g. 800 => 0x320 => 00000320 (big-endian) =>20030000 (little-endian)
def i2LeHexStr(i):
    be_hex = ('0000000'+hex(i)[2:])[-8:]
    n = 2 # split every 2 letters
    return ''.join([be_hex[i:i+n] for i in range(0, len(be_hex), n)][::-1])

BMP_HEADER = BMP_HEADER % (i2LeHexStr(len(aligned_pixels)/(BYTE/BPP)+BMP_HEADER_SIZE),i2LeHexStr(width),i2LeHexStr(height))

sys.stdout.write(Hex2Bytes(BMP_HEADER+aligned_pixels))

编辑：有关此电子纸显示的所有内容以及我在其上显示内容的代码，请访问：https://github.com/yy502/ePaperDisplay

Answer 2

看看https://en.wikipedia.org/wiki/BMP_file_format#File_structure。问题是您没有指定颜色表。根据维基百科文章，如果位深度小于8位，那么这些是强制性的。

Answer 3

在解决问题方面做得很好。您还可以考虑为ImageMagick创建个人委托或自定义委托，以帮助自动化该过程。 ImageMagick能够将不能自己处理的格式委托给代理人或助手，例如你的2位助手; - ）

您可以在/etc/ImageMagick/delegates.xml中创建自己的代理，而不是干扰可能位于$HOME/.magick/delegates.xml的系统范围代理。你的看起来像这样：

<?xml version="1.0" encoding="UTF-8"?>
<delegatemap>
  <delegate encode="epaper" command="convert &quot;%f&quot; +matte -colors 4 -depth 8 -colorspace gray pgm:- | /usr/local/bin/4_level_gray_4bpp_BMP_converter.py > out.bmp"/>
</delegatemap>

然后如果你跑：

identify -list delegate

您会看到自己被列为＆＃34;已知＆＃34; 帮助者。

这意味着您将能够运行如下命令：

convert a.png epaper:

它将自动执行2位BMP操作。

Answer 4

您可以使用此功能：

convert in.jpg -colorspace gray +matte -colors 2 -depth 1 -resize '640x384>' pgm:- > out.bmp**

Answer 5

我也有这个电子纸显示器。经过反复试验，我能够使用以下命令使用ImageMagick正确转换图像：

convert -verbose INPUT.BMP -resize 300x300 -monochrome -colorspace sRGB -colors 2 -depth 1 BMP3:OUTPUT.BMP

Answer 6

这适用于Imagemagick 6.9.10.23 Q16 Mac OSX Sierra

输入：

convert logo.png -colorspace gray -depth 2 -type truecolor logo_depth8_gray_rgb.bmp

http://www.fmwconcepts.com/misc_tests/logo_depth8_gray_rgb.bmp

添加-type truecolor可将图像转换为RGB，但按照-colorspace grey采用灰色调。深度2在直方图中仅创建4种颜色。

将图像转换为索引的2位灰度BMP

6 个答案: