AI GigaPixel to Reduce to Specific File Size

It would be nice if GigaPixel had an option to change a file to a certain size in MB.

For instance, Zenfolio has a 67 MB maximum file size. After processing Nikon D850 photos, I have had some JPGs grow to as much 95 MB. (How a 51MB nef grows this large after processing with Luminar and Sharpen AI is beyond me.)

Instead of guessing the proper image dimensions to get under the limit, it would be great if I could set the file size in MB and have GigaPixel work it’s magic.

Nice, but I’m not sure how practical that would be.

Gigapixel does not give any indication of expected export file size, and there is possibly a good reason for that.

While it is relatively easy to calculate an approximate file size for a non compressed image file, arriving at one for a compressed image file is a whole different ball game.

The size of a compressed image file depends on a number of things,including

(a) which format is used (JPG, TIFF with LZW compression, TIFF with ZIP compression etc)
(b) Any “quality” setting made (For example with Gigapixel JPG exports, the Image quality setting chosen)
© the content of the actual image itself (identical pixel size images can compress differently)

The only way I’m aware of to get an accurate file size indication prior to writing the file, is to effectively have the software do all of the processing, except for the actual file write itself.

Now to have it work backwards, to resize an image such that a specified file size is obtained would I believe require some form of iteration, and might be unacceptably slow.

But maybe Topaz can come up with a clever way to make it practical. :smiley:

This is my take on the question.

The Zenfolio size limit would have to be for an uncompressed file, it should not care what the compressed size is. Therefore, Gigapixel would have to only deal with the resizing of a picture to a new size in pixels. Instead of setting the resize to 4X or 6X, etc. there could be an option for file size which is easily calculated. Say you have a 2000px x 3000px file = 6 Mpx and you are using 24 bit color (8bits per R,G,B) where 8 bits = 1 byte. You would have 6 Mpx x 3 bytes per pixel or a 18 MB file. Since there are really 1048576 bytes per MB rated this would be 18.9 MB real size.

It doesn’t matter what format you save the file in or how it is compressed as these are all after the fact processing. As long as the aspect ratio and bit depth is known, (and that is a given) a program could calculate this backwards. Give it the file size in MB and it would give you the dimensions in pixels. However, this is rarely done so probably the reason it is not included.

Photoshop resizing does show the file size in MB when you enter the pixel dimensions but not the reverse.

I do have to say I am a bit confused how these files got that big.

I processed the NEFs (53mb lossless compressed 14 bit) in Luminar, exported to a JPG (about 51mb), but then ran them through Sharpen AI. The files ballooned to 70 to 95mb JPGs. The pixel dimensions did not change. Does Sharpen AI do something to the JPG compression?

I then used OnOne Perfect resize and reduce the size by 100 pixels , the files shrunk by more than half with no visible loss if IQ. (I tired shrinking with AI GigiPixel but that spent 15 to 20 minutes per image doing its thing.)

I don’t understand what happened to make these files so big.

Well it seems to be an absolute limit regardless of the file type, although it would appear Raw photos can be larger.

I agree that calculating W/H pixel dimensions to obtain a maximum uncompressed file size, knowing the image W/H ratio and the color depth would be relatively simple. That would however limit the pixel size of the exported image below what it could be if compression were used, and I’m not sure whether that would actually be suitable.