Markag wrote:
My neighbor... When downloaded and saved to my desktop/opened in PS it still says 212mb ! ! !
Can anyone explain this.
Yes, but the explanation is IS NOT simple.CHG_CANON is correct when he says that there is no direct correlation between file size and image size, with the caveat of saving files using compression, lossy or lossless. JPEG is a lossy compression file format.
Now a bit of a technical discussion
The very basic process for saving a JPEG is:
1) Original image is broken into image blocks (8x8 blocks)
2) Via the Discrete Cosine Transform, transform the image from the spacial domain to the frequency domain and quantize the DCT coefficients. The level of quantization determines the amount of compression.
3) Strip the high frequency content (luminance and hue) from the image. The content removed is, generally, not noticeable by most viewers.
4) data compression (Huffman encoding)
So the image loses information and is highly compressed in the frequency domain resulting in much smaller files for a given image size. Both, the frequency content and the amount of compression (user selectable) determines the file size (not image size). For example, if you were to save a pure white image with the same image dimensions and same compression factor as your flower image was stored as, the white image would be smaller because there is no high frequency content in it.
When the image is viewed, the software decodes the remaining info in the jpeg file and displays the lossy image. In most cases, the information lost is not perceptible to the viewer.
So, why work in the frequency domain? Representing an image in the frequency domain requires MUCH less data than in the spacial domain. If you have a technical background, you’ll know that time series such as a sine wave can be described with much less data in the frequency domain (via the FFT) than in the time domain. JPEG’s use this same advantage.
This is why JPEG file size and image size DO NOT correlate!Now back to the practical discussion.
There is 110MB of image data compressed into your 1.6MB JPEG file.
When you load your JPEG into Photoshop, Photoshop decodes the compressed image and stores it internally as 24-bit pixels, uncompressed (8 bits of R, 8 bits of G and 8 bits of B). In your case, your 1.6MB file is expanded to an uncompressed 110MB file internally. That allows PS to manipulate each individual pixel in the image. So here is a basic calculation on what the image size in bytes should be.
(7379 x 5021pxl) x (24 bits/pxl) / (8 bits/byte) = 111MB
Which corresponds to PS’s doc size.
AND, if you save your file as an uncompressed TIFF file, the resulting file size is 111 MB.
If you convert your image bit depth from 8-bit to 16-bit, the resulting TIFF is 222MB.
Hope this helps,
Mike
PS: Feel free to PM me if you have any specific questions about my response.