A little help needed - concerning the Computing with the Amstrad magazines

[Gryzor]

 Hello guys,


After it was brought to my attention that I haven't uploaded the CwtA mags I dug them scans up from my archives and was ready to up them until I saw that this thing is huge - some issues are as much as 350MB, a total of 3.2GB, clearly a LOT for a relatively small archive. The images aren't super-sized, so I guess the compression (jpg) must be really low.


So my question is, anyone can recomment a mass processing tool to convert them to png (my favorite) or compress them some more?


Cheers
T

[arnoldemu]

imagemagick command-line tools will do it for linux.

[Gryzor]

I'd prefer a windows solution, one that hopefully could give me a preview of the result...or even a Linux program with a GUI for that matter. Thanks anyway!

[McKlain]

Have you tried with XnView?

[gerald]

Irfanview provides batch processing.

However, I doubt that PNG compression will result is smaller file than JPG.
Can you share samples ?

[Gryzor]

Yes, I'll upload a couple of images. Surprisingly (for me) you're right, a 1.5MB image turned into a 2.5MB png, so it'll just be resaving and recompressing. I'll try both Irfan and XN, though I discovered that Directory Opus (best damn file manager out there) also has this function! It can't recurse directories though, which I think is the case with both image viewers mentioned above.


Thanks, guys!

[Bryce]

Then you need to reduce the size or the compression quality. You need to do a few tests to see how low you can go and still be completely readable.

Bryce.

[rexbeng]

In order for the PNG to be of smaller size, then you need to save as PNG in the first place (and in the case of scanning it depends on a few parameters). Converting JPG to PNG always results in files bigger than the JPG source.


rb

[Gryzor]

 @Bryce: yes, that's what I meant... tomorrow I'll upload a sample.
@Rexbeng: ahhh this makes a lot of sense, I realise now it has bothered me for some time!

[Gryzor]

Ok, here's a sample...

[gerald]

That's a 100% 4:4:4 jpeg  , the best quality you can get with jpeg. This explain the file size.
This is good tradeoff for preservation as there is no visible compression artefact and better size than png.

The same @85%  4:2:2 (sub sampling of chroma), most used encoding format.
The file is 4 times smaller

[Gryzor]

Hey, are you a gfx artist?


I gathered it was 100% given the dimensions of the file, but how do you find that?


With regards to jpg I have found that generally 90% is a very good compression rate for its size; when I can afford it (small file to send for instance) I may up it to 95% though it doesn't offer much more.


Unfortunately your attachment is not visible...? [EDIT: ah, a reload fixed it] [EDIT2 but it's a small png??]

[gerald]

Not artist at all 

But used to scan a lot of things (photo/books/mag ..) for preservation.
I am mainly using GIMP for editing, and when saving a JPG picture it uses the same setting as the original file so you can see it.

Can you check the attachement (click on it ?)

[Gryzor]

The attachment seems to be a small png; do you see something else?


I still don't understand - does GIMP tell you that the file was saved with a 100% setting? IIRC this info is not in the jpeg's headers, partly because it doesn't make much sense (what if it's been resaved?)...

[gerald]

The attachment seems to be a small png; do you see something else?

If you click on the thumbnail (png) you should get the full size jpg. Do not ask me why , I did not expect this when posting.

I still don't understand - does GIMP tell you that the file was saved with a 100% setting? IIRC this info is not in the jpeg's headers, partly because it doesn't make much sense (what if it's been resaved?)...

I do not know how GIMP get this info, but it may deduce it from the quantization table ?

[Gryzor]

Nah, I still get a smallish png at another computer as well


I'll do a couple of experiments with GIMP, sounds interesting...

[gerald]

Nah, I still get a smallish png at another computer as well

Changed from inlined to end of post attachement.
Should be better now

[Axelay]

On the subject of scans in png format instead of jpg, I've just uploaded a couple of pages as a test for TAU 58 as png files with the colour depth reduced to 4 bit.  Any thoughts on the quality?  I uploaded TAU 55 as jpg files previously, but was not sure of the readability, felt like the type in listings might be border line, though the pages were still up to half a MB each.

[Gryzor]

@gerald: the attachment looks great at a fraction of the size... cheers.


@Axelay: it does look a bit rough around the edges, but it's very readable nonetheless. But we can't know whether it's the file properties or the original scan that does the 'roughness' effect, any chance of uploading different file?

[Border_7]

On the subject of scans in png format instead of jpg, I've just uploaded a couple of pages as a test for TAU 58 as png files with the colour depth reduced to 4 bit.  Any thoughts on the quality?  I uploaded TAU 55 as jpg files previously, but was not sure of the readability, felt like the type in listings might be border line, though the pages were still up to half a MB each.

It is readable for sure...as Gryzor mentioned.


If you read the magazine this way: File:TAU 55Page53.jpg - CPCWiki


All seems acceptable - even the type-ins. About the only thing that is hard to read is the super small print on the contents page...

[Axelay]

@Axelay: it does look a bit rough around the edges, but it's very readable nonetheless. But we can't know whether it's the file properties or the original scan that does the 'roughness' effect, any chance of uploading different file?

I'll upload some jpg versions of those pages for comparison on the weekend, though I guess they'd look much like the TAU 55 scans I did.

[AMSDOS]

With the book I've been scanning, I've noticed the size of the scan produces a detailed page larger than the dimensions of the book, today I tried a little experiment by measuring up the size of the book and using those dimensions to produce a resolution from that. The  weird thing about that was the Dimensions I put into the computer were different from the Dimensions of the Book by a few Centimetres. In the end I had to best guess what the Size on the computer would be, in the end what I came up with seemed to work, though I was still surprised with the size of my B&W page scans and after I reduced the size of the image the detail I guess was readable though beginning to suffer, which I thought was a surprise given it was the same dimensions as the Original Book which was all clear.

[Gryzor]

Well, to "produce a resolution from that" makes no sense if you're talking about on-screen viewing. You'd have to print it out to have "the same dimensions" since monitors and resolutions are different all over the place.


You can use this tool to calculate the scan size for a given dpi in order to have something of the same size once you print it...

[Border_7]

I'll upload some jpg versions of those pages for comparison on the weekend, though I guess they'd look much like the TAU 55 scans I did.

I imagine they would, and I think that is quite readable and OK.

With the book I've been scanning, I've noticed the size of the scan produces a detailed page larger than the dimensions of the book, today I tried a little experiment by measuring up the size of the book and using those dimensions to produce a resolution from that. The  weird thing about that was the Dimensions I put into the computer were different from the Dimensions of the Book by a few Centimetres. In the end I had to best guess what the Size on the computer would be, in the end what I came up with seemed to work, though I was still surprised with the size of my B&W page scans and after I reduced the size of the image the detail I guess was readable though beginning to suffer, which I thought was a surprise given it was the same dimensions as the Original Book which was all clear.

I don't know if this will help or not - but I put my scanner on 'Automatic' & 'JPG' and hit scan. It produced 4-5mb JPG files which were pretty good quality! BUT were quite huge in dimension and file size (I'm not sure Gryzor would appreciate thousands of scanned pages @ 4/5mb per page??) anyway - I then just shrunk them down to around 200-400KB (cropped a bit too of course) and I think that was generally fine in most^* cases.


* some program listings I left the pages a bit bigger. Also, some pages were a bit crooked and a wee bit trimmed off - which of course is the fault of the human not the scanner or file type.

[Gryzor]

We've still got lots of space to waste on the server (last count: 36GB!), but this doesn't mean a magazine should weigh in at half a gigabyte Especially since, basically, you don't gain much...