我想要转换一个 jpg 文件（一本书的两页照片）保存为 pdf 文件，目的是
- 使 pdf 文件在页面大小和大小方面看起来像常规电子书文件的页面
- 保持 pdf 文件中 jpg 文件的清晰度或清晰度
我使用以下命令：
convert test.jpg -resize 2500x3080 -units PixelsPerInch -density 300x300 test.pdf
-resize和选项-units希望-density实现我的目标。
但pdf文件看起来不像原始 jpg 文件，当我用缩放系数打开 pdf 文件，并用缩放系数100%打开 jpg 文件时。eog1
我想知道如何选择选项及其论点以尽可能接近我的目标？选择这些论点和选项有什么原则吗？
jpg 文件的属性如下。图像尺寸为 1024 x 786 像素。和X Resolution的Y Resolution意思是每英寸的像素数，那么X和Y方向每英寸有180个像素吗？
$ exiftool pg296.jpg
ExifTool Version Number : 9.46
File Name : pg296.jpg
Directory : .
File Size : 214 kB
File Modification Date/Time : 2008:02:28 08:40:10-05:00
File Access Date/Time : 2016:04:01 18:45:28-04:00
File Inode Change Date/Time : 2016:04:01 13:24:27-04:00
File Permissions : rw-rw-r--
File Type : JPEG
MIME Type : image/jpeg
Exif Byte Order : Little-endian (Intel, II)
Make : Canon
Camera Model Name : Canon PowerShot A510
Orientation : Horizontal (normal)
X Resolution : 180
Y Resolution : 180
Resolution Unit : inches
Modify Date : 2008:02:04 11:15:55
Y Cb Cr Positioning : Centered
Exposure Time : 1/40
F Number : 2.6
Exif Version : 0220
Date/Time Original : 2008:02:04 11:15:55
Create Date : 2008:02:04 11:15:55
Components Configuration : Y, Cb, Cr, -
Compressed Bits Per Pixel : 3
Shutter Speed Value : 1/40
Aperture Value : 2.6
Max Aperture Value : 2.6
Flash : Off, Did not fire
Focal Length : 5.8 mm
Macro Mode : Normal
Self Timer : Off
Quality : Fine
Canon Flash Mode : Off
Continuous Drive : Single
Focus Mode : Single
Record Mode : JPEG
Canon Image Size : Medium 2
Easy Mode : Full auto
Digital Zoom : None
Contrast : Normal
Saturation : Normal
Sharpness : 0
Camera ISO : Auto
Metering Mode : Evaluative
Focus Range : Auto
AF Point : Auto AF point selection
Canon Exposure Mode : Easy
Lens Type : Unknown (-1)
Max Focal Length : 23.1875 mm
Min Focal Length : 5.8125 mm
Focal Units : 32/mm
Max Aperture : 2.7
Min Aperture : 8
Flash Bits : (none)
Focus Continuous : Single
AE Setting : Normal AE
Display Aperture : 2.6
Zoom Source Width : 2048
Zoom Target Width : 2048
Spot Metering Mode : Center
Photo Effect : Off
Manual Flash Output : n/a
Focal Type : Zoom
Focal Plane X Size : 5.82 mm
Focal Plane Y Size : 4.37 mm
Auto ISO : 100
Base ISO : 50
Measured EV : 8.97
Target Aperture : 2.6
Target Exposure Time : 1/40
Exposure Compensation : 0
White Balance : Auto
Slow Shutter : Off
Shot Number In Continuous Burst : 0
Optical Zoom Code : 0
Flash Guide Number : 0
Flash Exposure Compensation : 0
Auto Exposure Bracketing : Off
AEB Bracket Value : 0
Control Mode : Camera Local Control
Focus Distance Upper : 0.53 m
Focus Distance Lower : 0 m
Bulb Duration : 0
Camera Type : Compact
Auto Rotate : None
ND Filter : Off
Self Timer 2 : 0
Flash Output : 0
Num AF Points : 9
Valid AF Points : 9
Canon Image Width : 1024
Canon Image Height : 768
AF Image Width : 2048
AF Image Height : 256
AF Area Width : 369
AF Area Height : 46
AF Area X Positions : -370 0 370 -370 0 370 -370 0 370
AF Area Y Positions : -49 -49 -49 0 0 0 49 49 49
AF Points In Focus : 4,7
Primary AF Point : 4
Thumbnail Image Valid Area : 0 0 0 0
Canon Image Type : IMG:PowerShot A510 JPEG
Canon Firmware Version : Firmware Version 1.00
File Number : 111-1152
Owner Name :
Canon Model ID : PowerShot A510
Date Stamp Mode : Off
User Comment :
Flashpix Version : 0100
Color Space : sRGB
Exif Image Width : 1024
Exif Image Height : 768
Interoperability Index : R98 - DCF basic file (sRGB)
Interoperability Version : 0100
Related Image Width : 1024
Related Image Height : 768
Focal Plane X Resolution : 4571.428571
Focal Plane Y Resolution : 4571.428571
Focal Plane Resolution Unit : inches
Sensing Method : One-chip color area
File Source : Digital Camera
Custom Rendered : Normal
Exposure Mode : Auto
Digital Zoom Ratio : 1
Scene Capture Type : Standard
Compression : JPEG (old-style)
Thumbnail Offset : 2560
Thumbnail Length : 3231
Image Width : 1024
Image Height : 768
Encoding Process : Baseline DCT, Huffman coding
Bits Per Sample : 8
Color Components : 3
Y Cb Cr Sub Sampling : YCbCr4:2:2 (2 1)
Aperture : 2.6
Drive Mode : Single-frame Shooting
ISO : 50
Image Size : 1024x768
Lens : 5.8 - 23.2 mm
Lens ID : Unknown 5-23mm
Scale Factor To 35 mm Equivalent: 6.1
Shooting Mode : Full auto
Shutter Speed : 1/40
Thumbnail Image : (Binary data 3231 bytes, use -b option to extract)
Circle Of Confusion : 0.005 mm
Field Of View : 54.0 deg
Focal Length : 5.8 mm (35 mm equivalent: 35.4 mm)
Hyperfocal Distance : 2.63 m
Lens : 5.8 - 23.2 mm (35 mm equivalent: 35.4 - 141.1 mm)
Light Value : 9.1