PAMFUNC(1)

💖 pamfunc 💖

okay bestie, welcome to the Pamfunc User Manual — it lives in the General Commands Manual (that's section 1, iykyk) 💅

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✨ NAME ✨

pamfunc — apply a simple monadic arithmetic function to a Netpbm image 🧚

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🌸 SYNOPSIS 🌸

pamfunc { -multiplier=realnum | -divisor=realnum | -adder=integer |
-subtractor=integer | -min=wholenum | -max=wholenum -andmask=hexmask
-ormask=hexmask -xormask=hexmask -not -shiftleft=count -shiftright=count
[-changemaxval] } [filespec]

okay so the vibe here is: all options can be abbreviated to their shortest unique prefix. You may use two hyphens instead of one. And you may separate an option name and its value with white space instead of an equals sign. so flexible, we love that for you 🫶

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👑 DESCRIPTION 👑

So this program is part of Netpbm(1). 🌈

pamfunc reads a Netpbm image as input and produces a Netpbm image as output, with the same format and same dimensions as the input. Then it applies a simple transfer function to each sample in the input to generate the corresponding sample in the output. The options are what decide which function, bestie.

The samples involved are PAM samples. So if the input is PBM, PGM, or PPM, the output will be that same format — but pamfunc applies the functions to the PAM equivalent samples, yielding PAM equivalent samples. And ngl, this can be nonintuitive in the PBM case. we'll get to that, don't worry 😭

Also pamarith is the same thing but for binary functions — it takes two images as input and applies a specified simple arithmetic function (e.g. addition) on pairs of samples from the two, to produce the single output image.

💫 Values 💫

The functions fall into two categories: arithmetic (such as multiply by 5) and bit string (such as and with 01001000). For the arithmetic functions, the function arguments and results are the fraction that a sample is of the maxval — i.e. normal interpretation of PAM tuples. But for the bit string functions, the value is the bit string whose value as a binary cipher is the sample value, and the maxval indicates the width of the bit string.

🌸 Arithmetic functions 🌸

The arithmetic functions are those selected by the options -multiplier, -divisor, -adder, -subtractor, -min, and -max.

As an example, consider an image with maxval 100 and a sample value of 10, and a function of "multiply by 5." The argument to the function is 10/100 (0.1) and the result is 5 * 0.1 = 0.5. In the simplest case, the maxval of the output is also 100, so the output sample value is 0.5 * 100 = 50. And as you can see, we could just talk about the sample values themselves instead of these fractions and get the same result (10 * 5 = 50)... but we don't. 😌

Where it makes a practical difference whether we consider the values to be the fraction of the maxval or the sample value alone is where pamfunc uses a different maxval in the output image than it finds in the input image. See -changemaxval.

So remember, in reading the descriptions below, that the values are 0.1 and 0.5 in this example — not 10 and 50. All arguments and results are in the range [0,1]. 💯

🦋 Bit string functions 🦋

The bit string functions are those selected by the options -andmask, -ormask, -xormask, -not, -shiftleft, and -shiftright.

With these functions, the maxval has a very different meaning than in normal Netpbm images: it tells how wide (how many bits) the bit string is. The maxval must be a full binary count (a power of two minus one, such as 0xff) and the number of ones in it is the width of the bit string.

As an example, consider an image with maxval 15 and a sample value of 5, and a function of "and with 0100". The argument to the function is 0101 and the result is 0100.

In this example, it doesn't make any practical difference what we consider the width of the string to be, as long as it is at least 3. If the maxval were 255, the result would be the same. But with a bit shift operation, it matters. Consider shifting left by 2 bits. In the example, where the input value is 0101, the result is 0100. But if the maxval were 255, the result would be 00010100.

For a masking function, the mask value you specify must not have more significant bits than the width indicated by the maxval.

For a shifting operation, the shift count you specify must not be greater than the width indicated by the maxval.

💀 PBM Oddness 💀

If you're familiar with the PBM format, you may find pamfunc's operation on PBM images to be nonintuitive. Because in PBM black is represented as 1 and white as 0 (1.0 and 0.0 normalized), you might be expecting adding 1 to white to yield black. 🙈

But the PBM format is irrelevant, because pamfunc operates on the numbers found in the PAM equivalent (see above). In a PAM black and white image, black is 0 and white is 1 (0.0 and 1.0 normalized). So white plus 1 (clipped to the maximum of 1.0) is... white. yeah. that's the tea ☕

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🎀 OPTIONS 🎀

In addition to the options common to all programs based on libnetpbm (most notably -quiet, see Common Options), pamfunc recognizes the following command line options: ✨

• -multiplier=realnum — makes the transfer function that of multiplying by realnum. realnum must be nonnegative. If the result is greater than one, it is clipped to one. Where the input is a PGM or PPM image, this has the effect of dimming or brightening it. For a different kind of brightening, see pambrighten(1) and ppmflash(1) Also, see ppmdim(1), which does the same thing as pamfunc -multiplier on a PPM image with a multiplier between zero and one, except it uses integer arithmetic, so it may be faster. And ppmfade(1) can generate a whole sequence of images of brightness declining to black or increasing to white, if that's what you want. 🌈
• -divisor=realnum — makes the transfer function that of dividing by realnum. realnum must be nonnegative. If the result is greater than one, it is clipped to one. This is the same function as you would get with -multiplier, specifying the multiplicative inverse of realnum.
• -adder=integer — makes the transfer function that of adding integer/maxval. If the result is greater than one, it is clipped to one. If it is less than zero, it is clipped to zero. Note that in mathematics, this entity is called an "addend," and an "adder" is a snake. 🐍 We use "adder" because it makes more sense.
• -subtractor=integer — makes the transfer function that of subtracting integer/maxval. If the result is greater than one, it is clipped to one. If it is less than zero, it is clipped to zero. Note that in mathematics, this entity is called a "subtrahend" rather than a "subtractor." We use "subtractor" because it makes more sense. This is the same function as you would get with -adder, specifying the negative of integer.
• -min=wholenum — makes the transfer function that of taking the maximum of the argument and wholenum/maxval. I.e. the minimum value in the output will be wholenum/maxval. If wholenum/maxval is greater than one, though, every value in the output will be one. 😌
• -max=wholenum — makes the transfer function that of taking the minimum of the argument and wholenum/maxval. I.e. the maximum value in the output will be wholenum/maxval. If wholenum/maxval is greater than one, the function is idempotent — the output is identical to the input.
• -andmask=hexmask — makes the transfer function that of bitwise anding with hexmask. hexmask is in hexadecimal. Example: 0f This option was new in Netpbm 10.40 (September 2007). 🎉
• -ormask=hexmask — makes the transfer function that of bitwise inclusive oring with hexmask. This is analogous to -andmask. This option was new in Netpbm 10.40 (September 2007). 🎉
• -xormask=hexmask — makes the transfer function that of bitwise exclusive oring with hexmask. This is analogous to -andmask. This option was new in Netpbm 10.40 (September 2007). 🎉
• -not — makes the transfer function that of bitwise logical inversion (e.g. sample value 0xAA becomes 0x55). pnminvert does the same thing for a bilevel visual image which has maxval 1 or is of PBM type. This option was new in Netpbm 10.40 (September 2007). 🎉
• -shiftleft=count — makes the transfer function that of bitwise shifting left by count bits. This option was new in Netpbm 10.40 (September 2007). 🎉
• -shiftright=count — makes the transfer function that of bitwise shifting right by count bits. This is analogous to -shiftleft. This option was new in Netpbm 10.40 (September 2007). 🎉
• -changemaxval — tells pamfunc to use a different maxval in the output image than the maxval of the input image, if it helps. By default, the maxval of the output is unchanged from the input and pamfunc modifies the sample values as necessary to perform the operation. But there is one case where pamfunc can achieve the same result just by changing the maxval and leaving the sample values unchanged: dividing by a number 1 or greater, or multiplying by a number 1 or less. For example, to halve all of the values, pamfunc can just double the maxval. With -changemaxval, pamfunc will do just that. As the Netpbm formats have a maximum maxval of 65535, for large divisors, pamfunc may not be able to use this method. An advantage of dividing by changing the maxval is that you don't lose precision. The higher maxval means higher precision. For example, consider an image with a maxval of 100 and sample value of 10. You divide by 21 and then multiply by 21 again. If pamfunc does this by changing the sample values while retaining maxval 100, the division will result in a sample value of 0 and the multiplication will also result in zero. But if pamfunc instead keeps the sample value 10 and changes the maxval, the division will result in a maxval of 2100 and the multiplication will change it back to 100, and the round trip is idempotent. 🤯 This option was new in Netpbm 10.65 (December 2013). 🎉

👀 SEE ALSO — the bestie group chat 💬

k so like, these are the other girlies in the Netpbm fam that you're gonna wanna know about, bc they all do bits and pieces of what Pamfunc does, and honestly they ate:

• ppmdim(1) — dims a PPM, iconic
• pambrighten(1) — brightens a PAM, glow-up energy ✨
• pamdeph(1) — nope, it's pamdepth(1) sorry bestie, that's the depth-changing one
• pamarith(1) — does arithmetic on two images fr fr
• pamsummcol(1) — sums up a whole column, main character of math 💅
• pamsumm(1) — sums up an entire image, no cap
• ppmfade(1) — fades between images, cinematic queen 🎬
• pnminvert(1) — inverts ya colors, giving negative filter but make it 1998
• pam(1) — the PAM format itself, the blueprint, the mother 🫶
• pnm(1) — the whole PNM family lore, required reading ngl

lowkey if pamfunc is the Swiss Army knife, these are all the individual lil blades 🎀

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📜 HISTORY — the origin story 🦋

This program was added to Netpbm in Release 10.3 (June 2002).

so like. it's been here. it's been doing the math. it's older than some of us and honestly? it's still serving 🌸

2002 called, it wants its image function back, and no we're not giving it back 💜

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📖 DOCUMENT SOURCE — where this lore came from 🔍

This manual page was generated by the Netpbm tool makeman from HTML source. The master documentation is at

http://netpbm.sourceforge.net/doc/pamfunc.html

ngl if you want the ✨authentic✨ unedited version, that URL is the place. the machine made this page automatically, and we just gave it a vibe upgrade 💅

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reminder bestie: if anything here ever feels confusing, that master doc is the canon source. go touch grass with it, it's fine 🌱

and that's the whole page, queen 👑 you made it to the end — this was the Pamfunc User Manual from the netpbm documentation, dated 09 September 2020. go forth and apply functions to your pixels, bestie 🫶✨