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I have been uploading my photos (800 x 600 pixels) as jpeg compressed with quality 12 (maximum). The file size is typically 150 KB. When I look at the image in Auctiva, the file size is typically 35 KB. So presumably Auctiva opens the jpeg and saves again at quality 5 (medium)? If that's the case, I might as well upload jpegs at quality 5 (medium) to start with? Have I understood this right?

When I compare my image before uploading with the images in Auctiva, I can clearly see an increased contrast and vibrance in the Auctiva version of the image. I think Auctiva must be adjusting the image in the upload process? With the type of items I sell, an adjustment is unfortunate - the image in Auctiva must represent the original item precisely. Can I stop this adjustment?

Any advice anyone can give would be greatly appreciated.
Original Post

I just checked with our developers who are responsible for the image upload and storage part of our system regarding your questions.

Yes, we do compress images that are uploaded before they are stored on the server, and so you aren't really any better off to upload maximum 'quality' (e.g minimum compression) images, as we will compress them.

Please note that we do NOT change the pixel dimensions of the image when compressing it, unless the image being uploaded is larger than our maximum which is 1280 x 1024. If it is larger, then we resize it down to the max pixel dimensions size I just gave.

Regarding increasing contrast or color vibrancy of images during upload, our site does not do that. If anything, our compression would likely reduce contrast and vibrancy, and most certainly won't increase either contrast or vibrancy over what you would see in an image viewed through an image editing tool like Photoshop, Adobe Elements, or similar.

Hope this information is helpful.
Hi Tony and Subsuper!

Thank you both for your help.

In future I'll compress my jpegs to "medium" (quality 5) before I upload. No noticeable loss of quality and I save disk space.

I'm puzzled about the visible difference in the image appearance when I look at the image embedded in Auctiva’s supersized image web page (viewed with Microsoft Explorer or with Google Chrome) contra the same image as the jpeg before uploading (viewed in Photoshop or with Windows Live Photo Gallery). The image is noticeably more vibrant in the Internet browser, particularly the orange colors. I'm at a loss for an explanation!

I deliberately keep to 800 x 600 pixels rather than using Auctiva's maximum of 1280 x 1024 pixels - for the type of things I sell, that's more than enough supersizing, and when the buyer looks at the supersized picture, he/she can see the Auctiva navigation buttons and the image at the same time without needing to scroll.

A side remark: It's rather impressive how fast an Auctiva employee (here Tony) jumps into these forum threads where relevant with their help. I don't think I've ever come across a similar company with such outstanding service.

Again, thanks for all the help,

Re the color difference you mention you see,as I said yesterday, we don't adjust colors or contrast during the image upload/save process on Auctiva so I can't offer any help there.

However, since you mention you are viewing your images in Photoshop, (I am familiar with it as I'm a long time PS user in my personal life) I'm wondering if what you are seeing is not related to how color profiles are handled with JPEGs. I did a little looking and found this post on the Adobe forums.

The post talks about color profile conversions (from Adobe color space to SRGB). It also discusses how saving the jpeg with color profile imbedded in them can affect how an image appears when viewed with certain browsers, some of which have at least some color management capability.

Hope this is of some value.
I can confirm that Tony is right. In Photoshop, under "save for web and devices" there's a preview button that gives a preview of how the image will end up looking in a browser window (which presumably means a web browser like Explorer without color management). And lo and behold the preview here looks exactly like the image in Auctiva's supersized-image web page. So this is a Photoshop and color management problem, nothing to do with Auctiva.

As Tony says, this is a lively subject on the Adobe Photoshop forum, which is where this thread really belongs. So I'll sign off here, and start reading the threads on the other forum. And many thanks to Tony for getting me on track!


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