Posting Images

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Moderator: GreenLake

Re: Posting Images

Postby TIM WEBB » Tue Mar 31, 2015 10:33 am

Whew ... glad it's not just me! ;-P

Thanks GL. I *did* try again last night after you had success, but no joy. I'll try again if I get a chance later today ...
Tim Webb
1979 DS2 10099 The Red Witch
(I used to be Her "staff", in the way dogs have owners and cats have staff, but alas no longer ... <pout>)
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Re: Posting Images

Postby GreenLake » Wed Apr 01, 2015 12:12 pm

ISP responded: " probably caused by our recent configuration changes, we've rolled back the previous configuration. Please try again and let us know if the issue still persists?"

Please try again. Also, please let me know next time what you tried. Uploading via gallery, uploading attachment, or just accessing certain pages. May (possibly) make a difference in diagnosing.
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Re: Posting Images

Postby TIM WEBB » Wed Apr 01, 2015 3:11 pm

GL, as I stated a few posts back, I had tried to upload both to the gallery and as an attachment. I think there may be an image size limit discrepancy: when you upload to the gallery, it states a max file size of 500K, but when you upload an attachment, it's 256K. I just re-sized the images to <256 and they upload fine with both methods.

Thanks for checking into it!
Tim Webb
1979 DS2 10099 The Red Witch
(I used to be Her "staff", in the way dogs have owners and cats have staff, but alas no longer ... <pout>)
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Re: Posting Images

Postby GreenLake » Wed Apr 01, 2015 3:48 pm

The image I uploaded for test purposes is the same for attachment and gallery. And I always resize them down. This one is 73KB.

For Windows "Resize My Photos" is solid and functional freeware, which hooks directly into the shell, so you can operate on the images directly from the Explorer listing. I personally use Photoshop's "save to device" tool, which gives best control of both pixel dimension as well as compression ratio. I am normally already in PS to crop the image or to correct exposure to bring out detail anyway.

For forum use, a maximal dimension of 800 pixels usually gives enough detail, but the limits are currently a bit higher.

If/when everybody has 4K screens, larger resolutions might make sense - for now, they are just annoying because they force the viewer to scroll (attachments seem to open in fixed size viewing areas).
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Re: Posting Images

Postby TIM WEBB » Wed Apr 01, 2015 3:58 pm

That is very odd! I see on the post where it shows image size, but don't see a size shown in the gallery ... ?
Tim Webb
1979 DS2 10099 The Red Witch
(I used to be Her "staff", in the way dogs have owners and cats have staff, but alas no longer ... <pout>)
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Re: Posting Images

Postby GreenLake » Wed Apr 01, 2015 4:02 pm

Firefox gives that info if you click on View Image Info.
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Re: Posting Images

Postby TIM WEBB » Wed Apr 01, 2015 4:16 pm

Yeah, I usually use PS to re-size and level-balance images. I don't have PS on the laptop so I just use Paint.
Tim Webb
1979 DS2 10099 The Red Witch
(I used to be Her "staff", in the way dogs have owners and cats have staff, but alas no longer ... <pout>)
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Re: Posting Images

Postby Alan » Wed Apr 01, 2015 4:25 pm

damaged mast step and forestay shackle.jpg
damaged mast step and forestay shackle.jpg (154.58 KiB) Viewed 13850 times


OK, we seem to be back in business. (Above, by the way, are the parts that let go when I ran my mast into a power line last year.)
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Re: Posting Images

Postby GreenLake » Wed Apr 01, 2015 4:27 pm

Tim,
Install Resize My Photos. Paint is fine for cropping and scaling, but does not compress images (AFAIK). For JPG, if you go to 50-75% image quality, the file size drops rapidly. For most images, the loss in fidelity is not an issue, nor are the small "jpeg artifacts" that this introduces. But for a site like this, keeping the images small, makes them load faster and allows us to store more images without having to pay more to the ISP for disk quota.
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Re: Posting Images

Postby TIM WEBB » Wed Apr 01, 2015 10:04 pm

I'll definitely check that out GL. Correct: with all raster files (jpg, tif, etc), file size is exponential compared to image size (X pixels per inch by Y pixels per inch), because such files are nothing more than a list of values on a color look-up table that is based on a 256 color binary scheme ...

I know this because I once wrote such a table for a very early, rudimentary graphics program that I was using at B&W, and I was trying to get it to "talk to" a very rudimentary slide making machine, which was not much more than a big box with an early color CRT pointed up at a 35mm SLR camera loaded with Kodachrome film ... ;-P
Tim Webb
1979 DS2 10099 The Red Witch
(I used to be Her "staff", in the way dogs have owners and cats have staff, but alas no longer ... <pout>)
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Re: Posting Images

Postby GreenLake » Thu Apr 02, 2015 12:58 am

JPEG stands for Joint Photographic Expert Group. They were the body that developed that file format. Key part of their expertise had to do with how to compress pictures without losing (too much) quality. (Could be the P stands for Picture, not sure, but not important in this context; I think it does so for MPEG where MP is Motion Picture)

If I select about 60% compression quality (or "medium" if your UI is simpler) then an 800x600 image showing the usual details for a forum image here, the file size comes out to about 100KB. That 100KB used to the be the limit, by the way on many forums, and I believe, in earlier years, even here. I find that below 75% compression you can spot some image degradation, but it tends to be subtle and require magnification to see. Below 50% it's very obvious, because artifacts start appearing around high contrast transitions. So, I'd aim for a 150-200KB file if you use 1024 as the longest side (1280x1024 is the largest allowed for the gallery).
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Re: Posting Images

Postby TIM WEBB » Thu Apr 02, 2015 10:02 pm

Sorry - was just trying to explain raster images in the simplest terms, like those we were using in the 80's, way before jpeg's came along ... ;-P
Tim Webb
1979 DS2 10099 The Red Witch
(I used to be Her "staff", in the way dogs have owners and cats have staff, but alas no longer ... <pout>)
TIM WEBB
 
Posts: 1208
Joined: Wed May 18, 2005 10:28 pm
Location: RIVERSIDE, CA

Re: Posting Images

Postby GreenLake » Fri Apr 03, 2015 2:05 am

Sorry Tim, wasn't sure what your were trying to get across, so my reply may have been at cross purposes.

Anyway, an 800x600 bitmap, stored with an 8-bit color index would need something a little over 240,000 bytes, With 24bit color values, it's three times that.

So,I ran a little test with Alan's image, which is a bit smaller than that. Saved from Paint as a BMP it takes 667KB, as JPG it takes 53KB and as PNG it takes 321 KB. The JPG does loose information, when I switch between it and either of the other formats there's a little flicker where it doesn't represent the roughness of the cast aluminum part quite the same, but without that direct comparison you'd never know. It's not an entirely fair test, because the source was a jpg file to begin with, so it never had more information in it than the 153KB of the file size listed for the attachment.

With PS, if you save the file with "maximum" fidelity in jpg format, you get 153KB, essentially the original file. If saved with 50% quality, form "save for devices" in PhotoShop, the size is an astonishing 22KB (and degradation is not obvious). The reason, of course is that the image is largely an expanse of detail-poor background, and the surfaces of the parts are smooth.

So, as a result the relation between pixel dimension and the data required for a usable image is highly variable. With a good image resizer, it's quick and easy to massage your forum pictures a bit to make them both more friendly to be viewed in a post, and save some storage.

I tried the same sample with ResizeMyPhotos on Windows and the result was 18KB for the "medium", or 70% quality setting. So, that's even smaller than Photoshop uses for the 50% setting.

Anyway, enough fun playing with image compression.
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Re: Posting Images

Postby druidae1492 » Sun May 29, 2016 12:55 pm

Hmmmm. doesn't seem to be my cup of tea. I'm going sailing, not going to be a programmer. If you want to see a nice DS, look at someone elses or go check mine out on FB where uploading video is encouraged. FB name is David John.
We can not control the weather, we can only adjust our sails.
Freyjanna. Hull 10179, sail 1786.
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Re: sheet and halyard sizes

Postby GreenLake » Mon Jun 29, 2020 10:29 pm

I like this suggestion, originally posted in a different thread:
RobH912 wrote:The easiest way I’ve found for the picture size work around for this site using an iPhone is to mail the pictures from your phone to yourself (phones always ask about attachment size), use your computer, open the mail, save reduced size photo to a separate folder (not back to your photo library) and then post the reduced size photo from your computer. Pretty easy once you get the hang of it... and posts with pictures provide so much information to others for them to comment on the topic.
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