Why is a simple B&W line drawing 4 megs?

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llewelyn
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Why is a simple B&W line drawing 4 megs?

Post by llewelyn »

I tried Googling this query but got no useful responses!

Its a pencil on paper 8x10 I scanned (perhaps that's the answer, the scanning?)

Here it is, it comes up looking rather gray which is also odd but says 'load full resolution' then mentions that its 4.7 megs to do so. All you get is a bit brighter white, otherwise unchanged.

https://ibb.co/1RW86H3
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Re: Why is a simple B&W line drawing 4 megs?

Post by d2010 »

In my computer. That files is.
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Ast A. Moore
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Re: Why is a simple B&W line drawing 4 megs?

Post by Ast A. Moore »

JPEG compression is adjustable, so it doesn’t have to be four megabytes. However, JPEG is lossy, and the amount of data retained vs. lost determines the size of the file.

Now, simple images with little variation in them, will compress well without losing much quality. However, in your example, the texture of the paper is very complex—essentially random. Compressing it while preserving the detail is not possible without scarifying the resulting file size.

To you, the drawing is “simple,” because you’re only breaking it down to two elements: the “lines” and the “paper.” To the compression algorithm, it’s immensely complex, because each macro block consists of too many irreducible variations.

If you want to decrease the file size, boost the contrast and exposure of the image to the point that you start losing all the detail in the paper texture. Once it becomes fairly uniform, the file size will be reduced dramatically. You can also then specify the compression ratio.

For example, I just played around with it a little, and got it down to 326 KB. After I uploaded it to TinyPic, it got even smaller (with some additional loss in quality):

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Seven.FFF
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Re: Why is a simple B&W line drawing 4 megs?

Post by Seven.FFF »

1) You have a lot of pixels - 3049 x 2086 is nearly 6 and a half million, and data for each one has to be stored separately, albeit in a compressed/simplified form.

2) It's not a black and white image, you have a lot of very similar shades of grey, with each pixel next to another pixel of a different shade, which all adds up to a lot of unnecessary noise in the image. See the attached close-up.

3) You saved as a JPG, at high quality. This is very good at compressing un-noisy images, and very good at reducing the amount of detail in non-noisy images. But really sucks with this image and the quality settings you used.

4) Presumably this is a line drawing you scanned yourself. Most of the noise comes from the settings you choose when you scanned it. With line drawings it's always best to adjust the scanner settings so your paper is pure white, and your darkest lines are pure black. If the image is scanned perfectly flat and doesn't have dirty marks, you will find your image is still in grey scale, but most of the intermediate greys between white and black are in useful places, on the edges of the lines where they will soften the jagged effect and give a realistic copy of the source image. For this scan, most of the grays are "wasted" on areas of the paper which should be entirely white.

In short, like with everything, there's better ways and worse ways to do everything, and you have to understand the ways you're using, and the implications of them. Scanning images isn't immune from that, although it might seem like a simple thing you don't need to pay much attention to. And also, the suboptimal choices you make tend to compound each other so you have an extremely non-optimal result.

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Last edited by Seven.FFF on Tue Jul 09, 2019 4:35 pm, edited 1 time in total.
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Seven.FFF
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Re: Why is a simple B&W line drawing 4 megs?

Post by Seven.FFF »

Another thing you could probably say, is that pencil is not a great choice for precise drawings. It's great at conveying subtle shading in looser art forms, and some architects can make it work for them by adopting a style that's both precise and loose (by emphasising points and line ends, while relaxing the intermediate parts of lines). But it does tend to pick up and emphasise the texture of the paper, and leaves a wider, less distinct line, even when you use the harder H grades. This is particularly noticeable when scanned.

But generally, pen and ink (Rotring pens? Sketching fountain pen if you wanted a slightly looser style?) works better for precise lines. It's no coincidence that comicbook artists rough out in pencil, ink over, then erase the pencil. It would certainly result in a crisper image, which should also transfer more easily to the limited Spectrum resolution and colour depth, if you wanted to do that.
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llewelyn
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Re: Why is a simple B&W line drawing 4 megs?

Post by llewelyn »

Thanks very much everybody - SevenFFF, Ast. A. Moore, D2010 - for taking the time to explain that. I don't use a scanner much and so had no idea that it 'sees' black and white like that, crumbs, all those greys - who'd a thunk it? No wonder that file is that big. Well I live and learn, won't make that mistake again!
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