Bulk export tile image/why does cropping increase size?

[PaulSutherland]

Hi all,

Brand new Irfanview user here. I have TIFF files that I would like to split into even parts (keeping TIFF format), which is what led me to Irfanview's "Export tile image" function. I would like to know if it's possible to perform this exact function in bulk. Looking through the guide for command line options (http://www.etcwiki.org/wiki/IrfanVie...d_Line_Options) I cannot see any option to call the export tile image function.

I tried using the bulk crop and rename tool, and while this works nicely, the exported TIFF files are much larger than the imported TIFF files. For example: using "export tile image", a 42mb file split into 2 columns and 1 row would end up with two 21mb files - this is ideal. Using bulk crop, however, results in each crop being around 80mb, and therefore almost quadrupling the size of TIFFs. I am not specifying any additional processing (e.g. color, contrast) between the import and export TIFFs, and so I cannot work out how that can be the case.

Is anyone able to offer help, either with a method to bulk export tiles from images, or to bulk crop and rename without changing the total size of the file on disk?

Thanks,
Paul

[Bhikkhu Pesala]

Check your compression options. The difference in file size is most likely due to not using the same compression method as used by the original.

I don't see any option for doing this as a batch process.

[PaulSutherland]

Check your compression options. The difference in file size is most likely due to not using the same compression method as used by the original.

I just checked and I have it set to Compression: "None" on the options for output.

I don't see any option for doing this as a batch process.

I figured that might be the case. Is there a possibility it could be implemented? Having the same output as input file size using batch crop would be fine if possible though.

Thanks for your quick response.

[Bhikkhu Pesala]

I just checked and I have it set to Compression: "None" on the options for output.

So, change it to LZW or Zip to reduce the file size. JPG will also reduce the quality.

PNG can also be used for lossless compression, and it may be smaller than TIF.

You could run four batch operations on the original TIF images to crop to a different quadrant on each run. A plain crop can be run from a command line.

[PaulSutherland]

Thanks. I will test those out tomorrow at work but I am curious to know if there is a crop option that doesn't compress from the original or add anything else in. We need as high a quality as possible and it seems odd that the files increase in size. I don't know much about compression though I'll admit. Is LZW lossless? We can't zip them just yet.

It seems like tile option keeps the image identical except for dimensions, and I'd like crop to do the same.

Regarding running several batch operations, yes, that's what I'd do. It works great, I just need nothing to happen to the size ideally.

[Bhikkhu Pesala]

If the size increases then the original is compressed, but the cropped version is not.

Lempel–Ziv–Welch (LZW) is a universal lossless data compression algorithm created by Abraham Lempel, Jacob Ziv, and Terry Welch. It was published by Welch in 1984 as an improved implementation of the LZ78 algorithm published by Lempel and Ziv in 1978.

Zip compression is also lossless. The compression is done when saving the data in the TIF file to a TIF file. It is not the same as zipping the TIF file.



The results will vary depending on the image data, but here is a comparison of different compression methods used on the same image. All but the JPG image and TIF with JPG Compression are lossless.



Note that the PNG image has the smallest file size among the lossless methods. The 24-bit image has 30,849 unique colours

[PaulSutherland]

Thanks! That's really helpful.

I just re-tested the "none" compression option on scans I recently made, and unlike what I encountered before, file size does not change at all, as desired. I am confused as to what can have happened before. I changed none of the options from yesterday. I guess that's my problem solved. Thank you for your help.

If it's ever in the pipeline to have a batch option for "Export image tiles", that would be fantastic. I can make my own thread in that section of the forum if that's convenient.