PNG to Base64 string

[Jacob Wall]

To demonstrate how a PNG to Base64 is decoded and then encoded, I'll use a basic block of 3 bytes of data expressed in decimal format as {137, 80, 78}.

Step 1: Convert these bytes to binary format using SETBASE({137,80,78},1). The result is {#10001001b,#1010000b,#1001110b}

Step 2: Format as string, making sure each string is 8 chars long, left-padding with zeroes where required, resulting in:
10001001 01010000 01001110

Step 3: Combine and then break into 6-bit chunks:
100010010101000001001110 to
100010 010101 000001 001110

Step 4: Format as binary integers to get:
{#100010b,#10101b,#1b,#1110b}

Step 5: Format as decimal integers SETBASE({#100010b,#10101b,#1b,#1110b},3) to get:
{#34d,#21d,#1d,#14d}

Step6: Look up the nth character in the Base64 alphabet (see https://en.wikipedia.org/wiki/Base64) for each integer to get:
iVBO

And so you iterate over each three byte block to compile the string, and in the end deal with any fractional remainders.

For anyone more familiar with these things; is there a quicker and simpler way to get from {137, 80, 78} to {34, 21, 1, 14} on the HP Prime? Any suggestions would be appreciated.