Python绘图保存为具有精确128x250像素的png？

Question

对于 eink 显示器，它需要使用恰好 128x250 像素的 png 文件。

从一个小的温度和湿度记录器中，我得到如下结果：

Date,Time,Temperature,Humidity
12.12.2021,17:02,23.8,48.9
12.12.2021,17:03,22.8,45.1
12.12.2021,17:04,22.7,44.5
12.12.2021,17:05,22.6,44.6
12.12.2021,17:06,22.6,45.4
12.12.2021,17:07,22.5,45.1
13.12.2021,13:02,23.8,48.9
13.12.2021,13:03,22.8,45.1
13.12.2021,13:04,22.7,44.5
13.12.2021,13:05,22.6,44.6
13.12.2021,13:06,22.6,45.4
13.12.2021,13:07,22.5,45.1
14.12.2021,19:02,23.8,48.9
14.12.2021,19:03,22.8,45.1
14.12.2021,19:04,22.7,44.5
14.12.2021,19:05,22.6,44.6
14.12.2021,19:06,22.6,45.4
14.12.2021,19:07,22.5,45.1

我使用 python 做了一些简单的绘图，比如（我是 python 中的一个小人物）：

from pandas import read_csv as pd
from matplotlib import pyplot as plt

Raspilog = pd('Temp.csv', header=0, squeeze=True)
Raspilog_CDate = Raspilog[Raspilog.Date == "13.12.2021"]


fig, ax = plt.subplots()
ax.plot(Raspilog_CDate.Time, Raspilog_CDate.Temperature, color="red")
ax2 = ax.twinx()
ax2.set(ylim=(0, 100))
ax2.plot(Raspilog_CDate.Time, Raspilog_CDate.Humidity, color="black")

plt.show()

结果如下：

但我需要它是 128x250 像素并保存为 png

我已经在互联网上阅读了有关 DPI 和英寸等的信息。在我看来，没有简单的解决方案:(有谁知道如何做到这一点？

Answer 1

您需要稍微调整一下 dpi（“每英寸点数”：每英寸的像素数）和 figsize（以英寸为单位）。 figsize 需要足够大以使文本 fig 有点合理。请注意，250x128 非常小，因此阅读文本会很困难。

以下代码是对一些可能的 dpi 进行试验的结果。 50 dpi 似乎还不错。

import matplotlib.pyplot as plt
import pandas as pd
import numpy as np
from io import StringIO

df_str = '''Date,Time,Temperature,Humidity
12.12.2021,17:02,23.8,48.9
12.12.2021,17:03,22.8,45.1
12.12.2021,17:04,22.7,44.5
12.12.2021,17:05,22.6,44.6
12.12.2021,17:06,22.6,45.4
12.12.2021,17:07,22.5,45.1
13.12.2021,13:02,23.8,48.9
13.12.2021,13:03,22.8,45.1
13.12.2021,13:04,22.7,44.5
13.12.2021,13:05,22.6,44.6
13.12.2021,13:06,22.6,45.4
13.12.2021,13:07,22.5,45.1
14.12.2021,19:02,23.8,48.9
14.12.2021,19:03,22.8,45.1
14.12.2021,19:04,22.7,44.5
14.12.2021,19:05,22.6,44.6
14.12.2021,19:06,22.6,45.4
14.12.2021,19:07,22.5,45.1'''
df = pd.read_csv(StringIO(df_str))

png_width, png_height = 250, 128
png_dpi = 50
fig, ax = plt.subplots(figsize=(png_width / png_dpi, png_height / png_dpi))
ax.plot(df.Time, df.Temperature, color="red")
ax2 = ax.twinx()
ax2.plot(df.Time, df.Humidity, color="black")
ax2.set_ylim(0, 100)

ax.set_xticks(np.arange(0, len(df), 2))
ax.set_xticks(np.arange(0, len(df)), minor=True)
ax.set_xticklabels(df.Time[0::2])
ax.tick_params(axis='x', which='both', length=4)
plt.tight_layout()
fig.savefig('Test250x128.png', dpi=png_dpi)

plt.show()

这会生成一个正好为 250x128 的 png：