如何在将 jpg 转换为 pdf 文件时保持清晰度?

如何在将 jpg 转换为 pdf 文件时保持清晰度?

我想将几个 jpg 文件(每个都是一本书的两页的照片)转换为 pdf 文件,目的是

  • 使 pdf 文件在页面大小方面看起来像普通电子书文件的页面,并且
  • 保持 pdf 文件中 jpg 文件的清晰度或锐度

为了简单起见,下面我只考虑一个 jpg 文件(即两页),我使用 ImageMagick:

convert test.jpg  -resize 2500x3080  -units PixelsPerInch -density 300x300 test.pdf

通过-resize-units-density选项希望能实现我的目标。

pdf 文件看起来不如原始 jpg 文件evince,当我使用缩放比例打开 pdf 文件时,并使用缩放比例100%打开 jpg 文件。eog1

我想知道如何选择选项及其参数来尽可能地接近我的目标,无论是否使用 LaTeX?

根据 jpg 文件的属性来选择这些参数和选项是否有一些原则?


jpg 文件的属性如下。图像大小为 1024 x 786 像素。X ResolutionY Resolution表示每英寸像素数,那么沿 X 和 Y 方向每英寸是否有 180 像素?

$ 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

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