我试图使用EPSON DS-40（由于其紧凑的特性）和Raspberry Pi 3B +来扫描文档。
我首先尝试了SANE项目，但没有成功，目前扫描仪被列为“未经测试”，软件可以识别扫描仪，但是在发送开始扫描命令时会超时。
然后我发现了专门为此扫描器here编写的一段python代码。此代码将开始扫描，但几秒钟后将报告错误消息：
usb.core.USBError：[Errno 110]操作超时
我发现代码中的行：
def read():
d = dev.read(EP_IN, IN_BUF_SIZE)
return bytes(d)
在读取命令上只需要超时，所以我将其更改为以下内容。
def read():
d = dev.read(EP_IN, IN_BUF_SIZE,10000) # the 3rd parameter adds a 10000ms timeout
return bytes(d)
超时确实等待，但是10秒超时完成后仍然出现错误。我还尝试了无效的数据包大小（IN_BUF_SIZE）。
我发现，如果我打印出从USB端口读取的整个字节流，则扫描将完成并得到图像。
然后我发现接收大量数据包后发出了睡眠命令，而不是打印，扫描操作将始终成功。
def read():
d = dev.read(EP_IN, IN_BUF_SIZE)
inbuffer = np.array(d, dtype=np.uint8)
if(len(inbuffer) > 10000):
sleep(4)
return bytes(d)
我的问题是，实际上是什么原因引起的？有没有更简单的方法来解决此问题？这个问题是由于Raspberry Pi实现了Python USB吗？
这是我正在运行的完整修改后的代码，原始代码只需访问github链接即可。我所做的唯一修改是上面提到的3条额外的行
#!/usr/bin/env python
# dsforty.py - Scan a page on Epson DS-40
# Copyright 2015 (C) Mansour Behabadi <mansour@oxplot.com>
from subprocess import Popen, PIPE
from collections import deque
import argparse
import atexit
import os
import sys
import tempfile
import threading
import usb.core
import usb.util
from time import sleep
import numpy as np
IN_BUF_SIZE = 1024 ** 2 #2 ** 19
VENDOR = 0x04b8
PRODUCT = 0x0152
EP_OUT = 0x02
EP_IN = 0x81
MAX_W = 8.5 # in inches
MAX_H = 14 # in inches
CLRS = {'g': b'M008', 'c': b'C024'}
BLANKS = {'g': 45, 'c': (44, 45, 45)}
BLANK_VARI = 25
MIN_HFEATURE_LEN = 0.3937 # in inches ~ 1mm
def find_edge(line, blank, vari, streak_thresh):
streak = 0
low = [max(0, c - vari) for c in blank]
high = [min(255, c + vari) for c in blank]
for pi, p in enumerate(line):
for c, cl, ch in zip(p, low, high):
if c < cl or c > ch:
streak += 1
if streak > streak_thresh:
return pi - streak + 1
break
streak = 0
return 0
def main():
def arg_range(low, high):
def fn(v):
v = int(v)
if v < low or v > high:
raise argparse.ArgumentTypeError(
'must be in range %d..%d' % (low, high))
return v
return fn
parser = argparse.ArgumentParser(
formatter_class=argparse.RawDescriptionHelpFormatter,
description='Scan a page on Epson DS-40'
)
parser.add_argument(
'-r', '--res',
choices=[300, 600],
default=300,
type=int,
help='scan resolution - defaults to 300 dpi'
)
parser.add_argument(
'-c', '--color',
choices=list(sorted(CLRS)),
default='c',
help='scan color: `g` for grayscale and `c` for color'
' - defaults to color'
)
parser.add_argument(
'-q', '--quality',
type=arg_range(1, 100),
default=100,
help='quality of output JPEG, between 1..100 - defaults to 100'
)
parser.add_argument(
'-n', '--no-crop',
action='store_true',
help='do not crop vertical borders - use when autocrop messes up'
)
args = parser.parse_args()
# Setup device
tmpout = tempfile.TemporaryFile(mode='r+b')
sys.stdout = open(sys.stdout.fileno(), 'wb')
dev = usb.core.find(idVendor=VENDOR, idProduct=PRODUCT)
if dev is None:
print('DS-40 is not available', file=sys.stderr)
exit(1)
atexit.register(lambda: usb.util.dispose_resources(dev))
dev.set_configuration()
def read():
d = dev.read(EP_IN, IN_BUF_SIZE, 1000)
inbuffer = np.array(d, dtype=np.uint8)
if(len(inbuffer) > 10000):
sleep(1)
return bytes(d)
def write(d):
dev.write(EP_OUT, d)
write(b'\x1c\x58') # put scanner in control mode
if read() != b'\x06':
print('scanner didn\'t ACK control mode', file=sys.stderr)
exit(1)
# Setup parameters:
# COL sets image type as defined by CLRS{}
# GMM sets gamma: (UG10 -> 1.0, UG18 -> 1.8)
# CMX sets color correction: (UNIT -> disable, UM08 -> for C024)
# RSM, RSS sets resolution
width, height = int(args.res * MAX_W), int(args.res * MAX_H)
params = deque()
params.append(b'#ADF#COL')
params.append(CLRS[args.color])
params.append(b'#FMTJPG #JPGd%03d#GMMUG18#CMXUNIT' % args.quality)
params.append(
b'#RSMi%07d#RSSi%07d' % (args.res, args.res))
params.append(b'#ACQi%07di%07di%07di%07d' % (0, 0, width, height))
params.append(b'#PAGd000#BSZi%07d' % IN_BUF_SIZE)
for gmt in (b'RED', b'GRN', b'BLU'):
params.append(b'#GMT' + gmt + b' h100')
params.append(bytes(range(256)))
params = b''.join(params)
write(b'PARAx%07X' % len(params))
write(params)
if b'#parOK' not in read():
print('scanner didn\'t accept params', file=sys.stderr)
exit(1)
# Start scanning
write(b'TRDTx0000000')
ret = read()
if b'#errADF PE' in ret:
print('no paper to scan', file=sys.stderr)
exit(1)
final_height = None
while True:
write(b'IMG x0000000')
ret = read()
if not ret.startswith(b'IMG x'):
print('bad image data ack', file=sys.stderr)
exit(1)
if b'#errADF PE' in ret:
break
pen_idx = ret.find(b'#peni')
if pen_idx >= 0:
final_height = int(ret[pen_idx + 13:pen_idx + 20])
dl = int(ret[5:12], 16)
while dl > 0:
d = read()
dl -= len(d)
tmpout.write(d)
threading.Thread(target=dev.reset, daemon=True).start()
tmpout.flush()
tmpout.seek(0)
if final_height is None:
print('no final height reported', file=sys.stderr)
exit(1)
# Analyse the output for better cropping if PIL is available
left, right = 0, width
try:
from PIL import Image
except ImportError:
if not args.no_crop:
print('PIL not installed - disabled autocrop', file=sys.stderr)
args.no_crop = True
if not args.no_crop:
vnorm = (lambda x: (x, x, x)) if args.color == 'g' else lambda x: x
line = [vnorm(p)
for p in Image.open(tmpout).crop((0, 0, width, final_height))
.resize((width, 1), 1).getdata()]
streak_th = int((MIN_HFEATURE_LEN / MAX_H) * len(line))
blank = vnorm(BLANKS[args.color])
left = find_edge(line, blank, BLANK_VARI, streak_th)
right = find_edge(reversed(line), blank, BLANK_VARI, streak_th)
right = width - right
if left >= right:
left, right = 0, width
print('couldn\'t find edges', file=sys.stderr)
tmpout.seek(0)
# Crop
jpegtran = Popen(
['jpegtran', '-crop', '%dx%d+%d+0' % (
right - left, final_height, left
)], stdin=tmpout, stderr=open(os.devnull, 'wb')
)
jpegtran.wait()
exit(0)
if __name__ == '__main__':
main()
更新：我发现仅在读取后添加睡眠并不能完全解决问题，我不得不将读取命令的超时从默认值增加到1000ms。我还发现可以将睡眠时间减少到1秒，并且仍然可以持续工作。
d = dev.read(EP_IN, IN_BUF_SIZE,1000)