influence of compression on pictures

[speckled wood]

Not seeking an argument here, simply guidance that might be useful for others. My policy is to use maximum file size compression on pictures submitted to the gallery, the reason for this being to minimise the space used on the system by my pictures and I recognise that the resulting effect of archiving can appear to add more noise to a picture, just wondering if the gallery editors would prefer people to do as I do or to use the maximum file size that the rules allow.

Generally on my files saved at home I avoid compression and maximise files sizes which in some case means 18 meg image files.

[glsammy]

The best way is to make sure your images are 880 pixels on the largest side. If you do this there is no further compression done to the image. That's why when you look at the image details you'll see two sizes quoted, one the uploaded size, and the other the reduced to 880 pixel size, if the image was larger than this.
That's why I always upload with an image size as close to 880 x 600 as I can get.

[eeyore]

Originally Posted by glsammy

The best way is to make sure your images are 880 pixels on the largest side. If you do this there is no further compression done to the image. That's why when you look at the image details you'll see two sizes quoted, one the uploaded size, and the other the reduced to 880 pixel size, if the image was larger than this.
That's why I always upload with an image size as close to 880 x 600 as I can get.

i generally resize to as close to 800x600 as poss then save on quality 7 in photoshop (ie medium compression. I'm not sure that the compression ratio has much effect on the quality of images for gallery upload (although I'm willing to be corrected by those with special jedi powers) as the gallery software resizes and recompresses everything uploaded to a standard size (or as close to it as the dimension allow) anyway.

certainly when the site is backed up everything is zipped up which is just another form of compression , and that doesnt seem to have damaged the images

[glsammy]

Originally Posted by eeyore

i generally resize to as close to 800x600 as poss then save on quality 7 in photoshop (ie medium compression. I'm not sure that the compression ratio has much effect on the quality of images for gallery upload (although I'm willing to be corrected by those with special jedi powers) as the gallery software resizes and recompresses everything uploaded to a standard size (or as close to it as the dimension allow) anyway.

certainly when the site is backed up everything is zipped up which is just another form of compression , and that doesnt seem to have damaged the images

Whilst I now size to 880, as this is the size the site software re-saves the image to, I've never noticed any difference in image quality when I've saved to 800! So provided your somewhere around that point, the image will look it's best. If it's at 800, then it gets left there, (At least I think it does!) So your image doesn't get re-compressed. Although even when I've loaded them at 1280, I still haven't noticed any drop in quality. So perhaps it just doesn't matter!

[eeyore]

Originally Posted by glsammy

Whilst I now size to 880, as this is the size the site software re-saves the image to, I've never noticed any difference in image quality when I've saved to 800! So provided your somewhere around that point, the image will look it's best. If it's at 800, then it gets left there, (At least I think it does!) So your image doesn't get re-compressed. Although even when I've loaded them at 1280, I still haven't noticed any drop in quality. So perhaps it just doesn't matter!

I'm probably wrong but I thought Stu said it resized everything to 725pix on the longer edge (or possibly on the shorter edge, or something )

I think size matters more than compression as a 800x600 severely compressed still measures 800x600 when it is decompressed. where as to blow up a photo which is below the minimum dimensions would require significant interpolation - which in photoshop or genuine fractals doesnt matter but which with the gallery software probably does.

[glsammy]

Originally Posted by eeyore

I'm probably wrong but I thought Stu said it resized everything to 725pix on the longer edge (or possibly on the shorter edge, or something )

I think size matters more than compression as a 800x600 severely compressed still measures 800x600 when it is decompressed. where as to blow up a photo which is below the minimum dimensions would require significant interpolation - which in photoshop or genuine fractals doesnt matter but which with the gallery software probably does.

It's definitely 880 pixels on the largest side, it shows that on the info box with any over-sized image, showing the uploaded size and also the size as displayed, reduced to 880 pixels.
One of the main reasons the minimum size for the Gallery is 800 pixels is to prevent the problem you accurately describe.

[eeyore]

Originally Posted by glsammy

It's definitely 880 pixels on the largest side, it shows that on the info box with any over-sized image, showing the uploaded size and also the size as displayed, reduced to 880 pixels.
One of the main reasons the minimum size for the Gallery is 800 pixels is to prevent the problem you accurately describe.

I dont know where i got 725 from then mate - may be that was for the defunct upgrade , or maybe stu was talking about something completely different and I got confuddled

[matt_xyz]

I also agree that compression doesn't matter that much. Resize an image to 880 pixels on the longest size and then save at image quality 7 or 8 or thereabouts and this should ensure that the final file size is below 500kb (and preferably closer to 200).

Matt

[Oy]

Originally Posted by matt_xyz

I also agree that compression doesn't matter that much. Resize an image to 880 pixels on the longest size and then save at image quality 7 or 8 or thereabouts and this should ensure that the final file size is below 500kb (and preferably closer to 200).

Matt

^^^^ Good advice!

For screen viewing 7 or 8 in Photoshop (70-80%) is fine. Once you get to 6 or below image quality starts to suffer.