ImageMagick Convert BMP from 24 bit to 16 bit question?

Question

Trying to convert bmp file from 24-bit to 16-bit bmp by ImageMagick and ViX 統合画像ビュアー. This is the same as the thumbnail in my images, but in hex content is not my expected. And the question I ask because I have to covert these 16-bit bmp files to a .spr (Sprite image file) for MMORPG Game(Lineage 1).

• ImageMagickVersion: ImageMagick-7.1.0-portable-Q16-HDRI-x64
• ViX 統合画像ビュアー Version: ViX 2.21
• Plateform: Win11
• Source fils here
  1. Input_24bit.bmp
  2. Output_16bit_ViX.bmp
  3. Output_16bit_IM.bmp

ImageMagick Command

convert '24_bit.bmp' -alpha off -define bmp:subtype=RGB565 '16_bit.bmp'

ViX 統合画像ビュアー

Use GUI windows to decreasing color to Highcolor(16bit)

Result presenting (Red background will been transparent in Game)

BMP Hex Compare

• (A) result from ViX 統合画像ビュアー that I expected
• (B) result from Imagemagick convert
  

Answer 1

The difference is that ImageMagick, by default, writes a v5 BMP, whereas your program has written a v3 BMP.

To make ImageMagick write the older BMP3 format, prefix your output filename with BMP3: like this:

convert input.bmp -alpha off -define bmp:subtype=RGB565 BMP3:output.bmp