From: nospam <nospam@nospam.invalid>
Subject: Re: Windows freeware to lock in a 3: or 4:3 aspect ratio for cropping
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From: nospam <nospam@nospam.invalid>
Subject: Re: Windows freeware to lock in a 3: or 4:3 aspect ratio for cropping
Date: Sun, 18 Feb 2018 10:12:04 -0500
Organization: A noiseless patient Spider
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In article <p6c3kl$v3e$>, Mayayana<mayayana@invalid.nospam> wrote:

>    That's what all raster images are. Pixel grids. Bitmaps.
> No raster image format stores anything different. They
> just store it in different ways, with varying degrees
> of damage to the image.

there is no damage.

> JPG degrades the image to make
> it compress better, with less color variety. 

it's entirely up to the user what the jpeg quality/compression level
is, and at its highest quality, a jpeg is indistinguishable from the
original. this is very easy to demonstrate, should you not believe it.

> GIF reduces
> to 256 colors and compresses that. (256 colors requires
> an embedded color table, which takes up extra space,
> but then each pixel can be stored as a single byte.)

a colour table takes up very little space. 

> I don't know how PNG works


> but I'm guessing it's
> basically a BMP in a ZIP, with the addition of alpha
> channel data (transparency) requiring 4 bytes per pixel.


> (GIF, by contrast, stores transparency data by indentifying
> one specific color that's not to be painted onscreen.)

true, and primitive.

> TIF, likewise, is basically a BMP in a ZIP. 


> (Though a ZIP
> can often shrink a BMP by 90%,


simple logos with large areas of solid colours might shrink that much,
but certainly not with photos. logos would be better served with a gif
or png, not a zipped bmp.

> while a TIF seems to only
> manage about 50%. I don't know why.)

yep. you sure don't.

>    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.
> It has to be decompressed to get the BMP.

decompressed, yes, but no 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.

that part is mostly true. it's more complex than that, but i'll spare
you the details.

> It's all just math operations on 3-byte RGB pixels stored
> as grids in a BMP.

what you *refuse* to understand is that it doesn't have to be (and
normally is *not*) a bmp.

also, 3 bytes is horribly outdated. these days, it's two bytes per
component or it's a floating point value, with each pixel often having
more than 3 components (rgba, cmyk, hexachrome, etc.)

>    In other words, the idea that BMP is outdated is a
> misunderstanding of what raster images are. 

any misunderstanding is entirely with you.

bmp is obsolete. period.