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Progressive JPEG か Baseline JPEG かを判定する

Last updated at 2023-08-29Posted at 2023-07-31

準備

exiftool を使います。

brew install exiftool

サンプル画像

こちらを使います。

Download Sample JPG Image for Demo Use

Progressive JPEG の場合

Encoding Process が Progressive であることが確認できます。

curl -s https://example.com/cdn-cgi/image/width=150,height=150,fit=cover,format=jpeg/https://sample-videos.com/img/Sample-jpg-image-30mb.jpg \
| exiftool -

result.txt

ExifTool Version Number         : 12.60
File Size                       : 0 bytes
File Modification Date/Time     : 2023:07:31 11:30:34+09:00
File Access Date/Time           : 2023:07:31 11:30:34+09:00
File Inode Change Date/Time     : 2023:07:31 11:30:34+09:00
File Permissions                : prw-rw----
File Type                       : JPEG
File Type Extension             : jpg
MIME Type                       : image/jpeg
JFIF Version                    : 1.01
Resolution Unit                 : None
X Resolution                    : 1
Y Resolution                    : 1
Image Width                     : 150
Image Height                    : 150
Encoding Process                : Progressive DCT, Huffman coding
Bits Per Sample                 : 8
Color Components                : 3
Y Cb Cr Sub Sampling            : YCbCr4:2:0 (2 2)
Image Size                      : 150x150
Megapixels                      : 0.022

curl -s https://example.com/cdn-cgi/image/width=3000,height=3000,fit=cover,format=jpeg/https://sample-videos.com/img/Sample-jpg-image-30mb.jpg \
| exiftool -

result.txt

ExifTool Version Number         : 12.60
File Size                       : 0 bytes
File Modification Date/Time     : 2023:07:31 11:32:18+09:00
File Access Date/Time           : 2023:07:31 11:32:18+09:00
File Inode Change Date/Time     : 2023:07:31 11:32:18+09:00
File Permissions                : prw-rw----
File Type                       : JPEG
File Type Extension             : jpg
MIME Type                       : image/jpeg
JFIF Version                    : 1.01
Resolution Unit                 : None
X Resolution                    : 1
Y Resolution                    : 1
Image Width                     : 3000
Image Height                    : 3000
Encoding Process                : Progressive DCT, Huffman coding
Bits Per Sample                 : 8
Color Components                : 3
Y Cb Cr Sub Sampling            : YCbCr4:2:0 (2 2)
Image Size                      : 3000x3000
Megapixels                      : 9.0

Baseline JPEG の場合

Encoding Process が Baseline であることが確認できます。

curl -s https://example.com/cdn-cgi/image/width=150,height=149,fit=cover,format=jpeg/https://sample-videos.com/img/Sample-jpg-image-30mb.jpg \
| exiftool -

result.txt

ExifTool Version Number         : 12.60
File Size                       : 0 bytes
File Modification Date/Time     : 2023:07:31 11:34:03+09:00
File Access Date/Time           : 2023:07:31 11:34:03+09:00
File Inode Change Date/Time     : 2023:07:31 11:34:03+09:00
File Permissions                : prw-rw----
File Type                       : JPEG
File Type Extension             : jpg
MIME Type                       : image/jpeg
JFIF Version                    : 1.01
Resolution Unit                 : None
X Resolution                    : 1
Y Resolution                    : 1
Image Width                     : 150
Image Height                    : 149
Encoding Process                : Baseline DCT, Huffman coding
Bits Per Sample                 : 8
Color Components                : 3
Y Cb Cr Sub Sampling            : YCbCr4:2:0 (2 2)
Image Size                      : 150x149
Megapixels                      : 0.022

curl -s https://example.com/cdn-cgi/image/width=3000,height=3001,fit=cover,format=jpeg/https://sample-videos.com/img/Sample-jpg-image-30mb.jpg \
| exiftool -

result.txt

ExifTool Version Number         : 12.60
File Size                       : 0 bytes
File Modification Date/Time     : 2023:07:31 11:35:34+09:00
File Access Date/Time           : 2023:07:31 11:35:34+09:00
File Inode Change Date/Time     : 2023:07:31 11:35:34+09:00
File Permissions                : prw-rw----
File Type                       : JPEG
File Type Extension             : jpg
MIME Type                       : image/jpeg
JFIF Version                    : 1.01
Resolution Unit                 : None
X Resolution                    : 1
Y Resolution                    : 1
Image Width                     : 3000
Image Height                    : 3001
Encoding Process                : Baseline DCT, Huffman coding
Bits Per Sample                 : 8
Color Components                : 3
Y Cb Cr Sub Sampling            : YCbCr4:2:0 (2 2)
Image Size                      : 3000x3001
Megapixels                      : 9.0

参考

Check a JPEG is progressive or baseline | Sing's Log

参考： Cloudflare Image Resizing の挙動

Progressive JPEG - Supported formats and limitations · Cloudflare Image Optimization docs

While you can use the format=jpeg option to generate images in an interlaced progressive JPEG format, we will fallback to the baseline JPEG format for small and large images specified when:

The area calculated by width x height is less than 150 x 150.
The area calculated by width x height is greater than 3000 x 3000.
For example, a 50 x 50 tiny image is always formatted by baseline-jpeg even if you specify progressive jpeg (format=jpeg).

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