Picture formats#

This document describes the various picture formats used by CASIO or other software surrounding its calculators in protocols and file formats.

1bpp monochrome picture format#

This format is the basic frame format for fx-9860G calculators and compatible. It is used for internal VRAM representations, as well as for screenstreaming.

In this format, every pixel is represented as a bit, i.e. one byte contains 8 pixels. An off bit (0b0) represents a white pixel, and an on bit (0b1) represents a black pixel.

The picture is organized by row first, column second.

If the width is not divisible by 8, then the last bits of the last byte of the row are unused (fill bits), and the next row starts at the beginning of the next byte.

For computing the size of such pictures, one must compute the number of bytes a row occupies (usually ceil(width / 8)), then multiply it by the number of rows.

In Cahute, this format is represented by CAHUTE_PICTURE_FORMAT_1BIT_MONO.

1bpp monochrome picture format with CAS50 order#

This format is the basic frame format for pre-fx-9860G calculators using the CAS50 variant of CASIOLINK.

In this format, every pixel is represented as a bit, i.e. one byte contains 8 consecutive horizontal pixels. An off bit (0b0) represents a white pixel, and an on bit (0b1) represents a black pixel.

The picture is organized by descending column first, descending row second, 8 pixels by 8 pixels.

../_images/picture-format-1bit-cas50.svg — Pixel order in the 1bpp monochrome picture format with CAS50 order.#

For computing the size of such pictures, one must compute the number of bytes a row occupies (usually ceil(width / 8)), then multiply it by the number of rows.

In Cahute, this format is represented by CAHUTE_PICTURE_FORMAT_1BIT_MONO_CAS50.

Dual 1bpp gray picture format#

This format is one of the possible screen streaming formats for fx-CG (Prizm) calculators, using the 1RM2 algorithm.

This format is basically two pictures using 1bpp monochrome picture format placed back-to-back (with alignment), where the obtained colours are the following:

Bit from picture 1/2	Bit from picture 2/2	Obtained colour (`0xRRGGBB`)
`0b0`	`0b0`	`0xFFFFFF`
`0b0`	`0b1`	`0xAAAAAA`
`0b1`	`0b0`	`0x777777`
`0b1`	`0b1`	`0x000000`

For computing the size of such pictures, one must compute the number of bytes a picture occupies, and multiply it by two, i.e. 2 * ceil(width / 8) * height.

In Cahute, this format is represented by CAHUTE_PICTURE_FORMAT_1BIT_DUAL.

Multiple 1bpp picture format with CAS50 order and palette prefix#

This format is basically three pictures, also named “sheets”, using 1bpp monochrome picture format with CAS50 order placed back-to-back, with the exception that the picture is inverted vertically, i.e. you should use height - 1 - y instead of y.

Every sheet has an additional 1-bit prefix representing the palette color the picture represents:

Palette code	Corresponding color
`0x01`	Blue (`0x000080`)
`0x02`	Green (`0x008000`)
`0x03`	White (`0xFFFFFF`)
`0x04`	Orange (`0xFF8000`)

For computing the size of such pictures, one must compute the number of bytes a picture occupies, and multiply it by the number of sheets, i.e. sheet_count * ceil(width / 8) * height.

In Cahute, this format is represented by a different constant depending on the number of sheets:

For 3 sheets, CAHUTE_PICTURE_FORMAT_1BIT_TRIPLE_CAS50.

4bpp packed RGB picture format#

This format is one of the possible screen streaming formats for fx-CG (Prizm) calculators, using the 1RC3 algorithm.

In this format, every pixel is represented by a nibble (group of 4 consecutive bits), where, from high to low order:

If the first bit is on (0b1), then the red component is set.
If the next bit is on (0b1), then the green component is set.
If the next bit is on (0b1), then the blue component is set.
The last bit is an alignment bit, and can be ignored.

The picture is organized by row first, column second.

If the width is not divisible by 2, then the last pixel of every odd row and the first pixel of every even row share the same byte, and if the height is also odd, then the last 4 bits of the picture will be present as alignment.

For computing the size of such pictures, one must compute the number of pixels, divide it by two and round to the next integer, i.e. ceil(width * height / 2).

In Cahute, this format is represented by CAHUTE_PICTURE_FORMAT_4BIT_RGB_PACKED.

R5G6B5 picture format#

This format is the basic frame format for fx-CG (Prizm) calculators. It is used for internal VRAM representations, as well as for screenstreaming using the 1RC2 algorithm.

In this format, every pixel is represented by a 16-bit integer represented using big endian, where, from high to low order:

The first 5 bits represent the high 5 bits of the red component.
The next 6 bits represent the high 6 bits of the green component.
The last 5 bits represent the high 5 bits of the blue component.

The picture is organized by row first, column second.

The size of such pictures is the number of pixels multiplied by 2.

In Cahute, this format is represented by CAHUTE_PICTURE_FORMAT_16BIT_R5G6B5.

32bpp ARGB picture format using host endianness#

This format uses one 32-bit integer using host endianness for every pixel, organized by ascending row then ascending column.

This format is not used by CASIO, but declared as a possible picture format for conversion purposes.