如何在独立PostScript文件中嵌入并显示JPG图片？

Hey there! Let's get you sorted with embedding a JPG into a standalone PostScript file—no external dependencies or run required. I know those online guides can be hit-or-miss, so let's break this down step by step, tailored to your needs as a PostScript newbie.

First, the Basics #

PostScript Level 2 and above support direct JPG decoding via the DCTDecode filter, which handles the JPEG compression. The key here is to convert your JPG binary data into a format PostScript can read directly (like ASCII85) and embed it right in the script, so the file is completely self-contained.

Step 1: Prepare Your JPG Data #

You can't just paste raw binary JPG data into PostScript—you need to encode it into ASCII85, a compact ASCII encoding that PostScript natively understands with the ASCII85Decode filter.

To convert your JPG to ASCII85, use one of these simple methods:

• Python: Run this quick snippet (no extra libraries needed):

  with open("your_image.jpg", "rb") as img_file:
      jpg_bytes = img_file.read()
  import base64
  ascii85_encoded = base64.a85encode(jpg_bytes).decode("utf-8")
  print(ascii85_encoded)
  

• Command Line: If you have ImageMagick installed, use convert your_image.jpg ascii85:- to get the encoded output.

Copy the entire ASCII85 string—you'll need it for the next step.

Step 2: Write the PostScript Code #

Here's a complete, self-contained template. I'll explain each part so you understand what's happening:

%!PS-Adobe-3.0
%%BoundingBox: 0 0 595 842 % A4 page dimensions (adjust if needed)

% Move the drawing origin to 1 inch from left/bottom (72 PostScript points = 1 inch)
72 72 translate

% Image parameters: width, height, bits per component, transformation matrix
% Replace 300/200 with your image's actual width/height
300 200 8 [300 0 0 -200 0 200]
<<
  /ColorSpace /DeviceRGB   % Use /DeviceGray for grayscale images
  /DataSource (
    % PASTE YOUR ASCII85-ENCODED JPG DATA HERE
  )
  /DecodeParms << /Colors 3 >> % 3 for RGB, 1 for grayscale
  /Filter [/ASCII85Decode /DCTDecode] % First decode ASCII85, then JPEG DCT
>> image

showpage % Finalize and render the page

Critical Details to Get Right: #

1. Image Dimensions: Use the actual width and height of your JPG. To get this, run identify -format "%w %h" your_image.jpg (ImageMagick) or check your image properties in a viewer.
2. Color Space: Swap /DeviceRGB with /DeviceGray if your JPG is grayscale, and update /Colors in DecodeParms to 1.
3. Transformation Matrix: The [300 0 0 -200 0 200] part sets the image's position and orientation. The -200 flips the image vertically (since PostScript's origin is at the bottom-left, while JPGs are stored top-down).

Why Your Previous Attempt Failed #

Most likely, the issue was mismatched image parameters (wrong width/height/color space) or incorrect encoding of the JPG data. The head spacewar.asc step from that Stack Overflow answer was specific to a pre-encoded test file—your JPG needs its own correctly formatted ASCII85 data and matching parameters.

Testing the File #

Save the script as embedded_jpg.ps, then run it with Ghostscript (the most reliable PostScript interpreter):

gs embedded_jpg.ps

You should see your image rendered on an A4 page, no external files required.

内容的提问来源于stack exchange，提问作者TheFrozenDuck