From: J. P. Gilliver (John) <>
Subject: Re: Windows freeware to lock in a 3: or 4:3 aspect ratio for cropping
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From: "J. P. Gilliver (John)" <>
Subject: Re: Windows freeware to lock in a 3: or 4:3 aspect ratio for cropping
Date: Sun, 18 Feb 2018 15:22:25 +0000
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In message <p6c3kl$v3e$>, Mayayana<mayayana@invalid.nospam> writes:
>"J. P. Gilliver (John)"<> wrote
>| >That's true for lossless. But the cropping itself is always destructive.
>| Other than that cropping obviously removes information, what do you
>| mean: I thought the non-destructive crop was just that (in the part of
>| the image you keep, obviously). Being as it (as implemented in
>| IrfanView, anyway) crops to the nearest 16 (I think it's 16) pixel
>| boundary. I assumed the reason it does that is t avoid loss.
>  It's a clever method, but in general editing JPG
>is lossy. How often will one need to crop to the
>nearest 16 pixels but have no reason to do other
>editing? If one will do other editing then the image
>should be taken out of JPG format. So it's a kind of
>silk purse from a sow's ear thing.

Often, an image is only available as a .JPG: it might have been received 
in an email as such, or downloaded from a website; or, the majority of 
cameras other than those sold for the serious professional (with 
appropriate pricetags) do _not_ offer raw bitmap formats. (They 
sometimes offer three _quality_ levels.)
>   Nospam was just arguing, splitting hairs. It's
>really all he does.

Well, we all - including you and I, definitely - dislike imprecision, 
especially if it actually results in an untruth being stated (even if 
unintentionally). What level of simplification versus imprecision is 
acceptable, varies from person to person and between situations: in 
other words, one man's desire for precision is another man's 
hair-splitting. I can't say I've registered nospam as _particularly_ 
irritating in that respect, but that's mainly because I tend not to 
remember people's levels unless they're _particularly_ irritating (in 
which case I'm likely to killfile them, and haven't with him yet), so 
you _may_ be right.
>| >IMO, BMP should only be used when a software doesn't support a better
>| >format. How it stores 24bpp image pixels is unacceptably wasteful.

Re-reading that, I do agree it's oversimplifying - there _is_ no better 
format _in terms of accuracy_.
>| In what way - does it use two 16-bit words, or something? Or do you just
>| mean it doesn't do any (even lossless) data-compression?
>  It has no compression. It's very straightforward.
>In general a BMP will be a 24-bit, uncompressed

I was giving the benefit of the doubt: I thought he might have meant 
he'd found a case where it used 4 bytes to store the 3 byte information, 
or something. If he just means it does no lossy compression, I'd agree 
with you; if he means it does no loss_less_ compression, then he should 
have made it clearer that that' what he was referring to.

>image. (There are other options, but they're no
>longer used as far as I know.) The header looks
I _think_ the two-level (one _bit_ per pixel) form is still supported 
(e. g. by IrfanView), though I'm not sure if it includes a palette for 
the two colours. (I _think_ GIF does have such [and 2- and 4-bit - 4 and 
16 colour - modes.)
>   That's what all raster images are. Pixel grids. Bitmaps.
[Long section snipped - I presume written for readers other than me.]
>   They're all just ways to store a BMP. None of those
>image formats means anything until the BMP is extracted.
>One can't render a JPG onscreen any more than the words
>of a ZIPped Word DOC can be read from the ZIP bytes.

Good analogy! (Though I'd have probably said text file.)

>It has to be decompressed to get the BMP.
>   Similarly, when one applies filters in an editing program
>it's just a math formula applied to the bitmap bytes.
>Sharpening increases the difference between the numeric
>values. Interpolation for resizing calculates a new pixel
>grid by examining the values of neighboring pixels.
>Lightening increases the byte values of the pixel bytes.
>It's all just math operations on 3-byte RGB pixels stored
>as grids in a BMP.
>   In other words, the idea that BMP is outdated is a
>misunderstanding of what raster images are.
Well, I'm not sure if PNG can be lossless. (Actually, I'm not sure if 
JP[E]G can; I know the quality slider in IrfanView can be pushed up to 
100%, but I think that still involves some loss.)
Then, of course, there are vector images (like good old HPGL, as well as 
more modern ones) - let alone fractals! But for actual pictures taken 
with a camera, they're all going to be bitmap rasters in the first place 

[Actually, use of the word raster reminds me: true rendering of 
*archive* _video_ material (i. e. shot with a CRT camera) ought to 
involve a _slightly_ slanted raster - which, I think, no modern 
rendering does.]
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

And every day in Britain, 33 properties are sold for around that price [a
million pounds or so]. - Jane Rackham, RT 2015/4/11-17