Affinity Photo V2 file format conversion question

[thomB]

I know about lossless formats, and and lossy formats.. but here is something i experienced and no one really can help me understand. 

 

I had to do some cropping and converting to PNG format for some photos i wanted to have printed by Mpix

 

I had a jpeg file scan of a 35mm negative. The file size was 17.8 MB and the image size in pixels was roughly 5000x3200.  I did a crop of 2000x2500 and the file when converted to PNG was an interesting 53.8 MB.

I had nikon NEF  RAW images that when cropped to 2750x3500 pixels, the resulting PNG files were 98-101 MB. 

 

Can anyone explain how this actually works, because im only running a 1 TB drive.

[loukash]

PNG is a lossless compression. Saving photos as PNG will inevitably result in huge files, comparable to TIFF with LZW compression. The PNG format was primarily designed for online graphics, logos, symbols, pictograms etc., where it can make more efficient use of the lossless compression algorithm.

[walt.farrell]

38 minutes ago, loukash said:

PNG is a lossless compression. Saving photos as PNG will inevitably result in huge files, comparable to TIFF with LZW compression.

LZW is also lossless compression, so I'm not quite sure what you mean there.

[PaulEC]

51 minutes ago, loukash said:

Saving photos as PNG will inevitably result in huge files, comparable to TIFF with LZW compression.

I just tried exporting a picture as PNG and TIFF (with LZW compression) and the PNG fie was smaller than the TIF, so I'm not sure why you say that PNG with "invariably" be "huge" compared with TIFF!

[loukash]

9 hours ago, walt.farrell said:

I'm not quite sure what you mean there.

That saving an edited JPEG as PNG will result in files being magnitudes larger than the original, because PNG is lossless compression, and thus less efficient than the lossy JPEG compression.

9 hours ago, PaulEC said:

I just tried exporting a picture as PNG and TIFF (with LZW compression) and the PNG fie was smaller than the TIF, so I'm not sure why you say that PNG with "invariably" be "huge" compared with TIFF!

Depending on the source material, the PNG compression can be more efficient than the somewhat "antique" LZW compression in TIFF.
TIFF with LZW compression has several benefits though, like support for layers, CMYK color space, better IPTC/XMP integration, as well as the backwards compability compared to TIFF with ZIP compression.

As for the differences in size, I just picked up a random photo from an iPhone, saved as JPEG, 3.3 MB
Exported to PNG: 14 MB
Exported to TIFF+LZW: 16.5 MB

14 and 16.5 MB, that's what I mean by "huge" compared to 3.3 MB JPEG.
Then, in relation to the above comparison, 14 and 16.5 are still comparable in size.

So much for the semantics.  
Hope that helps.

~~~

Anyway.

@thomB, if file size matters (and it surely does), then export as JPEG "Best Quality" = "Quality: 100"
Taking my above example photo of originally 3.3 MB, a "Best Quality" JPEG will be about 6.3 MB, i.e. less than a half of what a PNG or compressed TIFF export would be.
At this setting and amount of pixels, a mere mortal won't be able to see any difference to PNG or TIFF.
Personally, I can barely see any difference even at the "JPEG High Quality" preset.

But as noted, it always depends on the source subject. There is no universal "fits-all" settings, one has to train the feeling for the subject so that eventually you'll be able to predict which compression or even format suits the final image the best.

[Xzenor]

The amount of noise heavily impacts the size of the png (maybe also other file formats, i don't know. I usually use png).

The resolution isn't always the biggest factor of the file size. A 10000x10000 picture of just one color is only a little over 310kb when exported as PNG. Add 5% of monogramatic gausian noise and it's almost 67MB. Non monogramatic makes it 127MB. All same resolution. just different pixels in it.

[walt.farrell]

1 hour ago, loukash said:

That saving an edited JPEG as PNG will result in files being magnitudes larger than the original, because PNG is lossless compression, and thus less efficient than the lossy JPEG compression.

I can agree with that, but was confused because you seemed to be comparing PNG compression and TIFF compression, which are both lossless. Thanks.

[smadell]

1 hour ago, loukash said:

if file size matters (and it surely does), then export as JPEG "Best Quality" = "Quality: 100"

I just opened a stock landscape photo (using Pexels inside of Affinity Photo) which measured 5,279 x 3,519 pixels. No edits were made at all. I exported the photo to various file formats.

TIFF (16 bit) with LZW Compression - 69.6 MB
PNG - 41.6 MB
JPG (100% Quality) - 21.9 MB
JPG (98% Quality) - 14.7 MB

The TIFF and PNG images are 16 bit files, and the JPG's are of necessity 8 bit files. Obviously the TIFF and PNG files are substantially larger, but also contain more information. Personally, I use TIFF's only as "interchange" files, such as when using a non-Affinity Raw developer and subsequently doing further editing in Affinity Photo. I use PNG files when I need to maintain transparency. I'll also use larger files (TIFF, PNG, PDF, or native .afphoto) when printing.

Otherwise, I rely primarily on JPG's. I've always found it interesting, though, that a huge amount of file size saving can be obtained by exporting JPG at 98% or so, instead of at 100%. The difference in perceptible quality (to me, at least) is nil; the difference in file size is considerable.

[loukash]

30 minutes ago, smadell said:

The TIFF and PNG images are 16 bit files

At 16 bpc, PNG compression is obviously more efficent than the good ole LZW. That's not necessarily surprising. As noted, a benefit of LZW compared to the more efficient ZIP compression is its backward compatibility.

37 minutes ago, smadell said:

the TIFF and PNG files are substantially larger, but also contain more information

If you were previously only "upsampling" from 8 bpc to 16 bpc without making any edits, then the extra 8 bpc will be just "padding", without an immediate benefit, and thus waste of storage space.

[walt.farrell]

1 hour ago, smadell said:

TIFF (16 bit) with LZW Compression - 69.6 MB

Previous discussions have pointed out that LZW (at least as used for TIFF) and 16-bit color depth don't work well together. 8-bit would probably give much different results.

[smadell]

1 hour ago, smadell said:

TIFF and PNG files are substantially larger, but also contain more information.

I guess I misspoke in this instance. The TIFF and PNG files, having been upscaled from 8 bit files, may not contain more information although they do contain more data.

The real reason for my post was to compare the file sizes in JPG at 100% and 98%, since the suggestion had been made to export at 100% JPG quality. The OP was concerned about large file sizes, given his limited storage capability. I suggested a way to attain smaller file size without (much) loss of perceptible quality.