I am trying to figure out if I can reduce optimised JPEG sizes further than what Photoshop can offer.
My boss has recently questioned whether the file sizes can be reduced using lossless JPEG's further than the sace for web function in photoshop.
From what I can make of it, lossy is the option on GIF files, and therefore I am assuming that the optimisation is lossless for a JPEG at 100 percent quality and lossy when the quality is reduced?
I just want to clarify that I am saving images for the web at the smallest size I can without losing too much quality.
All the images I save are 450px wide @ 75 dpi, but vary in length from 800px high to 1500px high, but have to be saved under 100kb.
Can anyone clarify the lossless and lossy in JPEG format in save for web?
JPEG is a lossy compression.
As c. says above, JPEG is a lossy compression - there is no lossless JPEG.
PNG 24bit offers lossless compression, that is it performs compression analogous to a zip archive, whereas JPEG works by (in extremely lay terms) building a new image that resembles the original.
GIF and PNG exports let you reduce the number of colours to get better compression - there are fewer pixel differences to compress at 8bit colour depth. Hence a 16 colour PNG will have a vastly smaller file size than a 24bit PNG, and depending on the image may be much smaller than a similar quality JPEG.
Depending on how far off your 100KB ceiling you are, you may be able to improve your file exports by cleaning up the source image - reduce noise and if possible explore exporting as 8bit pngs with fewer colours - avoid using diffusion or noise in the export options. Find the balance between acceptable file size and image quality... photographs tend to be the hardest thing to compress because there's so much detail data, especially in darker (low light) areas.