convert command is reducing the image size

[Prince7036]

ImageMagick version

ImageMagick 6.9.10-86

Operating system, version and so on

linux

Description

We are running the convert command to remove alpha channel

convert a.tif -alpha Off output.tif

Older version of convert (ImageMagick 6.5.7-0) produces an output tif with size 873kb but when running the same command in newer version (ImageMagick 6.9.10-86) results in a output file with size 366KB

which is causing further issues in our process

Did anything change in the newer version ? If so how do we retain the older behaviour ?

[dlemstra]

This sounds like the newer version has better compression. Can you share the input image and both output images?

[Prince7036]

Unfortunately I can't share the actual image. But I can share the tiffinfo output if that would help

Input tif file
TIFF Directory at offset 0x6569a (415386)
Subfile Type: (0 = 0x0)
Image Width: 2550 Image Length: 3300
Resolution: 300, 300 pixels/inch
Bits/Sample: 8
Compression Scheme: LZW
Photometric Interpretation: RGB color
Extra Samples: 1
Samples/Pixel: 4
Rows/Strip: 3300
Planar Configuration: single image plane
Predictor: horizontal differencing 2 (0x2)

ImageMagick 6.9.10-86 output
TIFF Directory at offset 0x5b558 (374104)
Image Width: 2550 Image Length: 3300
Resolution: 300, 300 pixels/inch
Bits/Sample: 8
Compression Scheme: LZW
Photometric Interpretation: RGB color
FillOrder: msb-to-lsb
Orientation: row 0 top, col 0 lhs
Samples/Pixel: 3
Rows/Strip: 3300
Planar Configuration: single image plane
Page Number: 0-1
White Point: 0.3127-0.329
PrimaryChromaticities: 0.640000,0.330000,0.300000,0.600000,0.150000,0.060000
Predictor: horizontal differencing 2 (0x2)

ImageMagick 6.5.7-0
TIFF Directory at offset 0xd38ca (866506)
Image Width: 2550 Image Length: 3300
Resolution: 300, 300 pixels/inch
Bits/Sample: 8
Compression Scheme: LZW
Photometric Interpretation: RGB color
FillOrder: msb-to-lsb
Orientation: row 0 top, col 0 lhs
Samples/Pixel: 3
Rows/Strip: 1
Planar Configuration: single image plane
Page Number: 0-1
DocumentName: test_ol6.tif
Software: ImageMagick 6.5.7-0 2018-03-09 Q16 http://www.imagemagick.org
Predictor: horizontal differencing 2 (0x2)

The major change I see is Rows/Strip which has not been changed in the newer version

[dlemstra]

As you pointed out Rows/Strip has changed between those version and without the files I cannot give you more information.

But I think it would be better to focus on the this comment instead

which is causing further issues in our process

Can you explain in more detail what kind of issues are you having?

[fmw42]

The input file (top listing) has

Extra Samples: 1
Samples/Pixel: 4

6.9.10-86 has

Samples/Pixel: 3
Page Number: 0-1

6.5.7-0 has

Samples/Pixel: 3
Page Number: 0-1

So different versions show different number of channels or pages. The top version has 4 channels and 1 extra channel. The bottom 2 have 3 channels and two pages.

I would not trust the bottom version of Imagemagick since it is so old. Lots of things have changed.

IM 6.9.10.86 is also a bit old. You should upgrade if you can. We are currently at 6.9.13-7 or even better upgrade to IM 7.

which is causing further issues in our process

What issues is this change causing you? I would think a smaller file size would be desired.