{PNG METADATA}

• {Author:} dpla.

• {Creation Time:} 2014-03-29 & 2023-02-05.

• {Title:} Monochrome gradient from RGBI-alike palette featuring Lenna.

• {Comment:} ZX Spectrum etc. computers related.

• {Description:} Filtering trial: from 24-bit (8-bit RGB) to Lanczos-filtered 4-bit near-RGBI (i.e. output as e.g. on the ZX Spectrum, but with a custom palette in its dim values: all trivially at 191 except for the magenta at 255 of blue, hopefully allowing a 15-gray gradient on B&W displays, hopefully smooth based on XnView and IrfanView renditions). Details of the 10-version composite (chart of 256 ื 256 pixels each in a 5-column ื 2-row layout) follow. Column #1: top = 'original'(*) [24-bit], bottom = GIMP2-filtered with Lanczos enabled [15 pseudo-colors as 4 bits indexed to the aforespecified 'RGBI']; column #2: top & bottom = same as column #1 but after 24-bit color filters (contrast esp.) in GIMP2; column #3: top = GIMP2-filtered with Lanczos enabled [15 grays as 4-bit index still with 8-bit RGB values], bottom = GIMP2-filtered with Lanczos enabled [2 grays as 1-bit index]; column #4: top = straight palette substitution (from the one on the left) [15 pseudo-colors as 4 bits indexed to the aforespecified 'RGBI'], bottom = ditto after slightly shifting 2 high values (a visual fix, hopefully too) [same colors and palette]; column #5: top & bottom = full desaturatiopn using XnView and IrfanView (gray-scaled versions before blending) from the previous column ['RGBI'], hopefully simulating a monochrome display [15-gray, 4-bit RGB].

• {Disclaimer:} These conversions may show a couple of flaws, at least.

• {Software:} GIMP; XnView, IrfanView; PaintNet; PNGGauntlet, pinga; TweakPNG.

• {Source:} Lenna (test image, 50 years after): Lena S๖derberg: http://people.zoy.org/~sam/gimp-dithering-2.png (*: downsampling likely by Samuel Hocevar, from the old sample available on Wikipedia.org as 512 ื 512 pixels).

• {Copyright:} Playboy magazine 1972-11. Photographed by Dwight Hooker.

• {Warning:} (SFW).