?? JPEG Compression Value

[nolanstern]

Hello,

What should I select as the JPEG compression value to make sure I am not compressing my images to the point where I am losing noticeable quality?

I am currently exporting my images at 1'24 X 768 or 768 X1'24 with resolution at 72 pixels to be viewed the on the web.

Can you make any suggestions about any changes I should make when exporting to web?

Also, I have Pantone Huey Pro Calibration kit but when I export to web I notice that my photos are a little lighter when viewed on the web than what is showing in LR. What could be the cause to this and how can I fix this.

Thanks for the help.
Chris

 

[Victoria Bampton]

For web I'd use 6'-8', something like that. And make sure you're exporting with sRGB as the colour space.

 

[nolanstern]

You mean 6'-8' pixels for resolution???

What about quality in the File Settings section? I have it set to JPEG, Quality = 1'' and Colour Space = SRGB...

 

[Anti]

> You mean 6'-8' pixels for resolution???
> I have it set to JPEG, Quality = 1''

Quality 1'' means no compression (largest files size).
If you set quality to 8', that means 2'% compression.
If I were showing off photos, I'd try 9'-85 (1'%-15%) compression to start with and adjust it depending on what files size I expect the user to download (and therefore how long they have to wait for the image to appear).

If I knew they wanted to see a nice, high quality photo that I'd taken, they will expect to wait a minute for a 5''kb image. For a normal, everyday website image in a blog or something, I would try to not let any one image file size go above 2''kb.

Personally, for showing off photos on screen (on a website), I would use 8''x6''. It isn't too big for the most used display-resolutions (around 7'% use displays between 1'24x768 and 128'×864). It means you can use a little less compression than for your 1'24X768 and obtain the same file size.

Forget the 'resolution' setting for your purpose. It doesn't matter until you want to PRINT. And whatever program you print in, it will let you choose the resolution at print-time. If you choose a larger resolution (say 3''), the better the quality, but the smaller the dimension (cm/inches) will be. For colour print, don't go below 24'; the printed image will be too pixelated.

 

[clee01l]

[quote author=nolanstern link=topic=7354.msg5'1'4#msg5'1'4 date=1248646'21]
You mean 6'-8' pixels for resolution???

What about quality in the File Settings section? I have it set to JPEG, Quality = 1'' and Colour Space = SRGB...
[/quote]Quality = Compression. i.e. 1''% means the least compression. Victoria is refering to the quality setting 6'-8'%. The 72 ppi is a meaningless term. your monitor may be displaying at 96 ppi, mine might be 12'. The browser displaying your photos will not resize unless it is instructed to. If you create an HTML image tag on your web page and do not specify a dimension, the image will display at 1 image pixel per 1 screen pixel. If you do specify a height or width constraint like 6'' px wide and the image is 1'24 px wide, the full image will be sent to the browser and resized in the browser to fit the width specified in the image tag. (A waste of bandwidth that will cause pages to display slower than necessary).

A quality/compression setting of 6'-8'% is 'good enough'. If you intend to share your photos on Flickr or one of the other photo hosting sites, you might want to send the site the highest quality possible. Everytime a JPEG image is compressed and decompressed, data is lost and after a few generations, your photo looks barely like the original. If you send a photo ot a host site, they will recompress it begore it is downloaded again resulting in some loss of quality.

About that 72 PPI number. The original EXIF specification states that when no PPI is specified, th default is used and the default is 72.

 

[nolanstern]

Thanks for the response...

Here are my settings I have set up to view on the web

File Settings:
Format - JPEG
Quality - 1''%
Color Space - SRGB

Image Sizing:
Height and Width - 1'24 X 768 or 768 X 1'24 Pixels
Resolution - 72 pixel per inch

I don't want to lose any compression as I want the best possible photo to appear when I post on the web so it is ok to change the quality to 6'-8'%...

Chris

 

[clee01l]

[quote author=nolanstern link=topic=7354.msg5'1'9#msg5'1'9 date=1248649585]I don't want to lose any compression as I want the best possible photo to appear when I post on the web so it is ok to change the quality to 6'-8'%...[/quote]I you don't want to lose data to compression, use 1''%. It is still compressed, but about the best you can do with JPEG. At 1'24X768, you are not talking about a large image (~.75MP) And today's web standards can easily accommodate that volume of data. If you really want to preserve all your data send uncompressed TIFF or uncompressed PNG (PNG is not supported in Lightroom btw).

 

[nolanstern]

Thanks for the help, Anti...

 

[Anti]

> If you intend to share your photos on Flickr or one of the other photo hosting sites,
> you might want to send the site the highest quality possible

True, but personally I would rather apply resizing and compression on my local computer than
trust a php script and apache to do things to the photo that are out of my control.

If the photo site I'm uploading to has published dimension and/or files size restrictions, I
would export the image locally to be within those restrictions so that no compression or
resizing was applied after uploading.

I think that a 1'24x768 image at 1''% quality would be about 8''-9''kb.
I don't know if that file size would trigger compression after uploading on Flickr.
Certainly on a normal blogging website it would be compressed to about 2''-4''kb.

But on a specialised image/photo sites, maybe they allow for larger file sizes.
I suppose it really depends on what sites these images are being uploaded to.
Best to do some tests using the actual site you're going to display them on.

 

[Victoria Bampton]

Just have a play with that compression setting - on most images there won't be visible compression above 7' odd (jpeg quality setting) and you shave a lot off the file size.