one bit transparency

[bitrat]

(11-05-2022, 08:40 PM)rich2005 Wrote: This has come up before see: https://www.gimp-forum.net/Thread-Export...with-Alpha

I do not know how you get a anti-alised 8-bit palette, even with Gimp 2.10 which throws in an extra indexed entry you just get 2 

Work-flow:
Black-on-White image
Colour-to-Alpha to make black on transparent
Mode -> Indexed 1 bit.

You do not say which OS you are using. If you can get a Gimp 2.8 that might work for you.



ImageMagick - Same as you, I can not see any way of getting a 1 bit png out.

Hi rich2005,

I just found that link myself but thanks!

My GIMP doesn't allow me to create a black+white (1-bit) image.  Minimum is 8-bit.

Every package seems determined to turn a bitmap into a grayscale at every opportunity, and to antialias screen rendering in the viewer, so it's often impossible to see whether the image itself is a bitmap or grayscale.  Even the window manager is probably involved in this...  Anyway, I'll update here when I've done some more experimenting. 

I'm using  GIMP 2.10.30 on Ubuntu 18.04.  Due for a system rebuild, but too much on to do it right now.. 

I'm using an AppImage, so maybe I'll try the older version with that.  
No AppImage for 2.8 I'll just need to manage with current limitations for now.  Basically, I'm trying to get pixel level control over grayscale rendering using the 'newsprint' dot screen filter.  It's very annoying to have this option removed, presumably based on the assumption that antialiasing and grayscale are always better....


Thanks again for the reminder to try ImageMagick, but sounds like it won't get me far...  I don't want extra steps in my workflow if I can help it, but it can be a lifesaver sometimes.

____________________________

UPDATE:

It looks like a PNG exported from a GIMP image created as per your suggestion is 8-bit RGB ...

Code:

$ identify test-1bit-alpha.png
test-1bit-alpha.png PNG 1024x683 1024x683+0+0 8-bit sRGB 4.48KB 0.000u 0:00.000

but it looks like it's 1-bit (black+alpha) under the hood, padded to 8-bits just to use extra disk space or some other misbegotten 'optimisation' ...

Code:

$ identify -verbose test-1bit-alpha.png
Image: test-1bit-alpha.png
  Format: PNG (Portable Network Graphics)
  Mime type: image/png
  Class: DirectClass
  Geometry: 1024x683+0+0
  Resolution: 118.11x118.11
  Print size: 8.66988x5.78274
  Units: PixelsPerCentimeter
  Type: Bilevel
  Endianess: Undefined
  Colorspace: sRGB
  Depth: 8/1-bit
  Channel depth:
    gray: 1-bit
    alpha: 1-bit
  Channel statistics:
    Pixels: 699392
    Gray:
      min: 0 (0)
      max: 0 (0)
      mean: 0 (0)
      standard deviation: 0 (0)
      kurtosis: 0
      skewness: 0
      entropy: -nan
    Alpha:
      min: 0 (0)
      max: 255 (1)
      mean: 51.7903 (0.203099)
      standard deviation: 102.588 (0.402306)
      kurtosis: 0.178562
      skewness: -1.476
      entropy: -nan
  Alpha: graya(0,0)   #00000000
  Colors: 2
  Histogram:
    557346: (  0,  0,  0,  0) #00000000 graya(0,0)
    142046: (  0,  0,  0,255) #000000FF graya(0,1)
  Rendering intent: Perceptual
  Gamma: 0.454545
  Chromaticity:
    red primary: (0.64,0.33)
    green primary: (0.3,0.6)
    blue primary: (0.15,0.06)
    white point: (0.3127,0.329)
  Background color: graya(0,1)
  Border color: graya(223,1)
  Matte color: graya(189,1)
  Transparent color: graya(0,0)
  Interlace: None
  Intensity: Undefined
  Compose: Over
  Page geometry: 1024x683+0+0
  Dispose: Undefined
  Iterations: 0
  Compression: Zip
  Orientation: Undefined
  Properties:
    Comment: Created with GIMP
    date:create: 2022-11-06T11:46:11+13:00
    date:modify: 2022-11-06T11:46:11+13:00
    icc:copyright: Public Domain
    icc:description: GIMP built-in sRGB
    icc:manufacturer: GIMP
    icc:model: sRGB
    png:bKGD: chunk was found (see Background color, above)
    png:iCCP: chunk was found
    png:IHDR.bit-depth-orig: 2
    png:IHDR.bit_depth: 2
    png:IHDR.color-type-orig: 3
    png:IHDR.color_type: 3 (Indexed)
    png:IHDR.interlace_method: 0 (Not interlaced)
    png:IHDR.width,height: 1024, 683
    png:pHYs: x_res=11811, y_res=11811, units=1
    png:PLTE.number_colors: 3
    png:text: 1 tEXt/zTXt/iTXt chunks were found
    png:tIME: 2022-11-05T22:46:11Z
    png:tRNS: chunk was found
    signature: 17cf50864f09dbe815449d6c9f96b0fabab283430f0375567ac4d732da83e9f7
  Profiles:
    Profile-icc: 672 bytes
  Artifacts:
    filename: test-1bit-alpha.png
    verbose: true
  Tainted: False
  Filesize: 4.48KB
  Number pixels: 699K
  Pixels per second: 69.94MB
  User time: 0.020u
  Elapsed time: 0:01.010
  Version: ImageMagick 6.9.7-4 Q16 x86_64 20170114 http://www.imagemagick.org

I may get there yet... 

Cheers,
bitrat