jpg in OpenCPN

[GPS-Marco]

Originally Posted by idpnd

Sorry I meant calibration of the Philippine charts

Sorry, this was not my intent.

This thread is about one guy that wants to calibrate phippine charts and that is looking around for the available tools. I adjusted one tool that I've used to calibrate hundreds of New Zealand Charts (KapGen) to help him. I can continue supporting anyone that wants to calibrate charts (philippines or others) but I've not enough spare time to calibrate other maps (apart from keeping update NZ charts...). Volunteers are needed here.

Ciao, Marco.

[idpnd]

Originally Posted by GPS-Marco

Volunteers are needed here

Hello Marco, I am well aware of your line of business, I was asking bewitched to publish the results - analogous to your own work

[bewitched]

Originally Posted by idpnd

I was asking bewitched to publish the results .

Don't see why not

Could be a while though... boat prep is sucking up all my spare time at the moment.

[bewitched]

Originally Posted by HappySeagull

It sounds like you found the button to reduce total size as a percentage?...?that'll keep the aspect ratio the same but it'll be a smaller image IE if you were looking at a narrow channel,the gps position icon could blot it out entirely,where on a BIG image you can happily fit between the banks and buoys...
Or did you find the button to change dpi as Sinbad was saying?

I came across something that reduces the number of pixels in each direction (and can be locked to maintain the x / y ratio). Yes, I think this is re-sizing the image. I couldn't find anything that mentions dpi (this is in GIMP2 by the way)

I hear what you're saying about maintaining the quality of the image. And I will be saving the originals for printoffs. But going from say 18,000 pixels in one direction to about 6,000 reduces the file size from +25MB to less than 8MB, with hardly a decernable loss in picture quality on the .jpg.

What I'll do is run several iterations of the whole conversion thing with varying original .jpg filesizes and then see which is the best fit when both file size and quality are considered.

Which I guess will be the best fit for me, based on the processing capability of my computer and what I would consider acceptable 'quality' of image.

[GPS-Marco]

Bewitched, I prepared KapGen to handle philippines large jpeg. See #26

I noticed that reducing size to 50% for philippines images is fine. The optimal number of colours is instead more image dependent and ranges from 16 to 64.

If you have questions, please ask.

Ciao, Marco.

[HappySeagull]

Originally Posted by bewitched

I came across something that reduces the number of pixels in each direction (and can be locked to maintain the x / y ratio). Yes, I think this is re-sizing the image. I couldn't find anything that mentions dpi (this is in GIMP2 by the way)

I hear what you're saying about maintaining the quality of the image. And I will be saving the originals for printoffs. But going from say 18,000 pixels in one direction to about 6,000 reduces the file size from +25MB to less than 8MB, with hardly a decernable loss in picture quality on the .jpg.

What I'll do is run several iterations of the whole conversion thing with varying original .jpg filesizes and then see which is the best fit when both file size and quality are considered.

Which I guess will be the best fit for me, based on the processing capability of my computer and what I would consider acceptable 'quality' of image.

Reducing colour depth will reduce file size.16 colours is half the size of 256 without changing the chart dimensions...

From your posts,it's hard to tell what recipe you are using but converting from jpgs is tricky and from my recipe you can see that fooling with images is harder than the cmd thing in description.


The originals willl always be blown up to size and bitdepth and it sounds like that bogs you down from the gitgo.

WHICH program are you using now?someone here will know it well to help.

idea:It's a possibility to "batch convert" just one image before you even have to look at it onscreen.Do this by opening any silly little picture in the image program and then look for the batchconvert dialogue to change the BIG jpeg.I'd try colour depth first....and save as bmp because it's native to windows.then size reduction.Later you can include all the best of your operations to several files in the one batch....

[GPS-Marco]

Originally Posted by HappySeagull

...I'd try colour depth first....and save as bmp because it's native to windows.then size reduction...

I'd do differently: size reduction first and colour depth later. This because a good image size reduction requires a spatial filter (like lanczos or bilinear or others...). The spatial filter works better in the RGB linear scale and it normally produces intermediate levels that increases the number of colours if you have reduced them to quantizied levels.

So I'd first reduce size and then colours depth.

Ciao, Marco.

[bewitched]

Originally Posted by GPS-Marco

Bewitched, I prepared KapGen to handle philippines large jpeg. See #26

I noticed that reducing size to 50% for philippines images is fine. The optimal number of colours is instead more image dependent and ranges from 16 to 64.

If you have questions, please ask.

Ciao, Marco.

I got that thanks - just haven't had time to try it out yet.

[bewitched]

OK - done

KAP files made for all Philippine charts I can lay my hands on.

Got a .rar file, but it's 2.6GB. Does anyone know where I can store this online for free so that people can download if they want?

Two charts that I'd really like and I haven't been able to get my hands on are (can't remember the no.s):
The chart with Hamilo Cove (and other Luzon Anchorages)
The chart with Port Bonbonon (and other Negros area anchorages).

If anyone has these charts / jpgs / whatever, I'd love a copy.

[idpnd]

Originally Posted by bewitched

KAP files made for all Philippine charts I can lay my hands on.

Got a .rar file, but it's 2.6GB. Does anyone know where I can store this online for free so that people can download if they want?

Are these all from the older US surveys that are now in the public domain? In that case it could be hosted with opencpn.

If the copyright is dubious, you could still elect to host it online somewhere as a backup and to compare notes with friends.

[bewitched]

Yes - the original Jpeg files I downloaded from the NOAA website "Historical Charts". The NOAA search page and function has since changed and I can't find them any more. But I did download them from NOAA - so I assume there's no copyright issue.

There may be the odd one which is a NAMIRA scanned copy - and so perhaps not too legit - I could weed them out for the opencpn site.

The charts are old - some very old. So where ever they are hosted, there'd have to be some very strong disclaimer about not being suitable for navigation and the posibility that I might have made mistakes in the calibration process. There are almost certainly errors in there.

So how does one go about uploading to opencpn then?

[idpnd]

There's a similar project by Marco, who has been calibrating the NZ charts for use as KAP files.

AFAIK NOAA charts are in the public domain as you quite rightly say. We may have to find the source to support this.

[sinbad7]

Bewitched..

You can add your charts here: 4shared - PHILIPPINES - shared folder - free file sharing and storage

Tore

[bewitched]

Originally Posted by idpnd

AFAIK NOAA charts are in the public domain as you quite rightly say. We may have to find the source to support this.

I've been trying to work out what AFAIK means, but can't get anything that fits without a great deal of profanity

OK - I found the charts again:

Office of Coast Survey Historical Map & Chart Image Catalog

It's a bit of a pain - The old webpage had a "download all Philippine Charts" option which was easy. This new all singing & dancing search page makes it much more difficult to get hold of a set of charts

There's no point using the word search - it doesn't come up with anything.

If you zoom into the Philippines on the map, click on the "click to select a point on map" button above the map. Then click at a location on the map, then you'll get a few charts around that area. So they are still there - just very difficult to find, and no way to find out if you have the full set.

But I guess that is enough to demonstrate the "public domain" bit.

[bewitched]

Hi Tore

Thanks for that link. I can upload a set for you not problem - but will be next week sometime.

The site looks like one of the better ones, but the 30 days login or loose everything isn't something I can live with.

My plan was to upload the files somewhere and then as I'm sailing around check the offsets etc, update and then replace the KAP files one by one as necessary. This is obviously going to take time. I'd hate to be in a position 6 months from now when I logon and find there's nothing there.