Ask Ubuntu General Room

user136984

4:00 PM

And I don't want someone just to be able to rename one of my storage files to a .bmp and then view it as one.

user136984

It will just become ridiculous then! :D

user136984

Well, for what its purpose is.

kos

@ParanoidPanda Then you're building a custom file format. First thing that comes to mind, if you don't need obfuscation, is to store the plain pixel matrix (somehow)

user136984

So I need to understand how image file formats currently work in order for me to make my own.

user136984

@kos: Also, while we're at it, how many colours can be displayed in a pixel?

kos

4:03 PM

@ParanoidPanda If you need compression it's going to be complicated, just look at the JPEG algorithm to get an idea. If you want to store the raw image, then you should be able to work out something easily

user136984

No, no compression.

user136984

But how many colours can a pixel have?

kos

@ParanoidPanda Don't take this for granted, but it should be 2^24

user136984

And what's the range in hex?

terdon

A pixel can only have one color as far as I know.

kos

4:05 PM

256*256*256, considering a gradation of red / green / blue represented on 8 bit

terdon

How could it have more? It's a pixel!

kos

@terdon Yes but the gradation of each channel should (this is almost a guess, but I think I'm recalling this) depend on the frequency applied to the led or whatever represents a R / G / B channel

user136984

So in the swatch in GIMP, exactly how many different colour variations are there?

terdon

@kos What does the LED have to do with it? A pixel is a dot, it is the smallest possible element of a bitmap. How can it have more than one color? That would imply splitting it into smaller pieces.

@ParanoidPanda Millions.

2^24 in 8bit but we are usually working in 32bit these days.

user136984

@terdon: For the maths to work I need to know an exact number.

kos

4:09 PM

@terdon I'm assuming @ParanoidPanda 's question is about how many colors can be displayed by a single pixel?

terdon

But what are you asking? How many colors can a single pixel have at the same time or how many colors can be displayed in general?

kos

Meaning how many possibilities, not how many at the same time. Of course at the same time it's only one!

user136984

@terdon: I'm not asking in a physical sense, I am just asking how many different colours there are that can be represented in an image file.

terdon

Oh.

user136984

@kos: Yes, that is what I mean.

terdon

4:10 PM

Well, in what mode? 8bit? 16? 32? 24?

user136984

32

terdon

2^32 then, I guess.

kos

@ParanoidPanda Ok so it's (2^n)^3, where n it's the number of bits used for the representation

terdon

> True color supports 24-bit for three RGB colors. It provides a method of representing and storing graphical-image information (especially in computer processing) in an RGB color space such that a very large number of colors, shades, and hues can be displayed in an image, such as in high-quality photographic images or complex graphics.

> Usually, true color is defined to mean 256 shades of red, green, and blue, for a total of 224 or 16,777,216 color variations. The human eye can discriminate up to ten million colors.

@kos And ^3 because of the three channels?

user136984

@kos @terdon: So it's "79228162514264337593543950336"?

kos

4:27 PM

@terdon No, I'm totally incorrect on this one: RGB24 contains 3 R / G / B color channels each represented on 8 bit, and RBG32 contains 3 R / G / B color channels each represented on 8 bit + a greyscale mask also represented on 8 bit

@ParanoidPanda For the above, the grand total for RGB24 is 16,777,216, multiplied by 256 for RGB32

@terdon But yes, the ^3 was because of the three channels

So each channel is always represented on 8 bit, it's the number of channels that defines the grand total of representable colors

kos

4:44 PM

@ParanoidPanda Also the range in hex should be from 0(dec) to 16777215(dec), which is 000000(hex) to FFFFFF(hex) on a 6 digit representation, which you might find more often represented as from 0x000000 to 0xFFFFFF

So back to your original question, you could store the plain bitmap using a matrix (represented using a different line of the text file for each row) whose values are in those ranges